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Ducted fans that are popular choices in vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) offer a higher static thrust/power ratio for a given diameter than open propellers. Although ducted fans provide high performance in many VTOL applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow is a significant source of aerodynamic loss for ducted fan VTOL UAVs and adversely affects the general aerodynamic performance of these vehicles. The present study utilized experimental and computational techniques in a 22″ diameter ducted fan test system that has been custom designed and manufactured. Experimental investigation consisted of total pressure measurements using Kiel total pressure probes and real time six-component force and torque measurements. The computational technique used in this study included a 3D Reynolds-Averaged Navier Stokes (RANS) based CFD model of the ducted fan test system. RANS simulations of the flow around rotor blades and duct geometry in the rotating frame of reference provided a comprehensive description of the tip leakage and passage flow. The experimental and computational analysis performed for various tip clearances were utilized in understanding the effect of the tip leakage flow on aerodynamic performance of ducted fans used in VTOL UAVs. The aerodynamic measurements and results of the RANS simulations showed good agreement especially near the tip region.

Behavior of water droplets in air is of interest in many engineering applications. In evaporative cooling, the evaporation of liquid droplets sprayed into air streams in measured quantities cools the air. In the current study, experiments and numerical simulations are carried out to investigate the thermo-fluid dynamic behavior of water droplets of different diameters in long air ducts. Droplet size measurements at different locations were obtained with global sizing velocimetry technique. Effect of initial droplet size on temperature and relative humidity distribution of air stream in the duct is investigated. Droplet spray patterns are also analyzed to identify suitable locations for spray nozzles within the duct. Cooling effectiveness is calculated for different conditions. Experiments were conducted to validate the numerical results. Results obtained provide a clear understanding of the thermo-fluid dynamic behavior of water droplets within the duct.Copyright © 2011 by KSME

The ability to design S-shaped ducts with high aerodynamic loading is advantageous from a performance and/or weight saving perspective. However, the radial pressure gradients required to turn the flow produce strong pressure gradients in the axial direction. This promotes the likelihood of flow separation from the inner casing as the loading is increased. The current paper presents a novel approach to accommodating the increased loading by bleeding an amount of air from the critical inner casing. The process through which the air is bled re-energizes the boundary layer sufficiently to enable it to remain attached despite the high duct loading. A bled duct is numerically developed and experimentally evaluated using a fully annular isothermal facility, with representative inlet conditions provided by a single stage axial compressor. The measurements indicate successful operation of this new design concept with a reduction in the overall system length, compared to a conventional design, of approximately 30% and a reduction in loss of approximately 20%. The data also demonstrate, to a limited degree, the ability to control the flow distribution at duct exit ultimately improving flow uniformity. Furthermore, the pressure of the bled flow is higher than at rotor exit where, in current engine architectures, flow is typically removed from the main gas path. In other words current engine bleed locations could be replaced by a bleed flow within the transition duct, and this flow is of sufficient pressure to meet the existing requirements associated with cooling, sealing and/or zone ventilation.

Bifurcation analysis is conducted on experimental data obtained from a simple setup comprising of ducted, laminar pre-mixed conical flames to investigate the features of nonlinear thermoacoustic oscillations. It is observed that as the bifurcation parameter is varied, the system undergoes series of bifurcations leading to characteristically different nonlinear oscillations. Through the application of nonlinear time series analysis on pressure and flame (CH* chemiluminescence) intensity time traces, these oscillations are characterised as periodic, aperiodic or chaotic oscillations and subsequently the nature of the obtained bifurcations is explained based on dynamical systems theory. Nonlinear interaction between the flames and the acoustic modes of the duct is clearly reflected in the high speed flame images acquired simultaneously with pressure and flame intensity measurements.Copyright © 2011 by ASME

This study highlights a mechanism of the vortex cavitation occurrence from the baffle plate, the end of the suction duct, in a double-suction volute pump and a relationship between pump oscillation and the cavitation occurrence. In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct. The numerical model is based on combination of multiphase flow equations with the truncated version of Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles. The vortex cavitation has the characteristic frequency based on the impeller rotation and has much influence on the pump oscillation, however at over discharge range the vortex cavitation does not collapse, because the cavitation runs into and combines with another cavitation generated in the impeller shroud, and the fixed frequency of the pump oscillation is reduced. The experimental investigations have also been performed on the cavitating flow to evaluate the numerical results and the both results agree well.Copyright © 2011 by JSME

The coupling of a sirocco fan, used to supply air to a mist sprayer, and a Diesel engine is studied in order to enhance the performance of the integrated system. In this case, the main problem for the correct design of the fan arises from the fact that it is not possible to define a priori the operating point. In fact, the rotational speed is not fixed as in the case of an electric motor driven fan, but is determined as an equilibrium of the power supplied by the engine and the power absorbed by the fan to recover the pressure drops of the mist sprayer system. In this paper, the experimental campaign performed to characterize the existent fans is presented. Moreover, the sprayer duct is characterized by using literature correlations and by performing numerical simulations. Then, the collected data are elaborated in order to scale the fans in order to enhance the performance of the system.Copyright © 2011 by ASME

The oscillating water column (OWC) is one of the more successful wave energy converters so far due to its mechanical and structural simplicity; there are no components for power take-off in seawater. Though there are some successful practical developments in bottom-fixed OWCs, floating OWCs are still in different stages of development. A specific oscillating water column, the OE Buoy (i.e. backward-bent duct device, ‘B2D2’), developed by OceanEnergy (Ireland), has recently attracted much attention. A 1:2.5 scale device has finished a sea-trial in Galway Bay (Ireland) for a period over two years during which period the device has gone through a severe storm. Thus its survivability has been confirmed to some extent. In this research, numerical simulations to the floating wave energy device are performed using a boundary element method code WAMIT. To consider the motions of the internal water in the column for energy extraction, a “numerical lid” is placed on the free surface in the column. In WAMIT, the motions of the “numerical lid” can be calculated by introducing relevant generalized modes to the conventional 6-DOF motions of the floating structure. For wave energy extraction, the “piston effect” of the internal water must be considered. To include the effect of the mooring system to the motions of floating structure, the mooring forces have been linearised, and their equivalent spring coefficients have been input to WAMIT for analysis of the moored floating structure. For the numerical simulation, the first case is to tune the damping coefficients based on wave tank results since in WAMIT, only hydrodynamic damping is included in calculation. In reality, larger damping may be needed to limit the large responses in heave of floating structure and the motion of the internal water surface. The tuned damping coefficients are then applied to the modified OWCs of different duct length, in which it is hoping that the corresponding responses of the internal free surface structure are used to assess the performance of the floating OWC. The aim of the research is to explore the relation between the OWC size and its performance so that it may provide a reference for optimizing the design of a floating OWC in the future.Copyright © 2011 by ASME

The proton exchange membrane fuel cell (PEMFC) has been regarded as promising alternative power sources for unmanned aerial vehicle (UAV). The temperature of PEMFC stack should be maintained an optimal range around 60∼80°C to prevent stack membrane damages at high temperature or low efficiency of stack at low temperature. Therefore, thermal management is crucial to maximize the performance of the PEMFC. Generally, the thermal management system (TMS) of PEMFC is composed of heat exchanger (HEX), fan, and pump. In this work, since the weight of UAV is one of the main factors to affect the UAV flight, the fan is eliminated. That means only the air flowing through the UAV is used to cool down the stack coolant water. Therefore a design optimization of HEX is important to get the best performance of PEMFC for UAV. The three dimensional numerical modeling has been developed by using the commercial code of STAR-CCM+®. In this simulation, the UAV body, circular-fin tube HEX, and duct are considered. Since the cruise velocity of the UAV is 40km/h, the air velocity at the duct inlet is set to be 40km/h. Heat exchanger is located at the top of the UAV, and the coolant water from the pump is flowing through the header and divided several tubes to increase the surface area of heat rejection rate or decrease the pressure drop. The mass flow rate of air flowing into each fin of HEX is determined by fluid analysis. In order to validate this model, the simulation results are compared with the experimental data, which is obtained at various coolant inlet temperatures, and coolant flow rates. And the parametric study of HEX model was conducted with various UAV velocities and air temperatures. One reference data point is selected to tune several unknown parameters in the model, and once established, the same parameter values are used for all other conditions. The simulation results are in good agreement with the experimental data. This model can be helpful to develop the optimal design of heat exchanger for UAV.

In recent years, steam is used in vane internal cooling ducts as a new coolant to replace compressed air. Much research has been carried out into the closed circuit steam cooling for vanes. But most of the existing literatures only provide information on the overall cooling effect of vanes. The effects of steam parameters on the cooling effectiveness of the vane internal channel are still not very clear. A steam heat transfer enhancement test platform of turbine blade (vane) internal channel at Equipment Cooling Technology Laboratory, Xi’an Jiaotong University was built to study the steam cooling characteristics in blade (vane) internal cooling channel. In this paper, heat transfer data of a steam-cooled duct have been experimentally obtained under different operating conditions. The range of key governing parameters is presented as follows: Reynolds numbers based on the channel hydraulic diameter (10000–60000), entry absolute pressures (0.3Mpa–0.6Mpa), heat flux of heat transfer surface area (5.5kWm−2 −22kWm−2 ), steam superheat (0K–40K). The results show that the average Nusselt numbers along the centerline of the ribbed wall of the steam-cooled square duct are about 15 percent higher than that of air, but the overall heat transfer characteristics of steam in the square duct are similar to that of air under the same conditions.Copyright © 2011 by ASME

Velocity measurements have been done in order to grasp the flow reattachment locations over a 3D backward-facing step in a duct by PIV for various Reynolds numbers from 200 to 1000. The aspect ratio and the expansion ratio of the stepped duct were 16 and 2, respectively. It was found that the flow reattachment location varies in the spanwise direction in every case. In the range of Re

CFD simulations were performed to study the flow and heat transfer in a rectangular duct (Wd × Hd , where Wd /Hd = 3) with a staggered array of circular pin fins (D = Hd /4) mounted on the two opposite walls separated by Hd . For this array of pin fins, five different pin-fin height (H) combinations were examined, and they are (1) H = Hd = 4D (i.e., all pin fins extended from wall to wall), (2) H = 3D on both walls, (3) H = 2D on both walls, (4) H = 4D on one wall and H = 2D on the opposite wall, and (5) H = 3D on one wall and H = 2D on the opposite wall. The H values studied give H/D values of 2, 3, and 4 and C/D values of 2, 1, and 0, where C is the distance between the pin-fin tip and the opposite wall. For all cases, the duct wall and pin-fin surface temperatures were maintained at Tw = 313.15 K; the temperature and the speed of the air at the duct inlet were uniform at Tinlet = 343.15 K and U = 8.24 m/s; the pressure at the duct exit was fixed at Pb = 1 atm; and the Reynolds number based on the duct hydraulic diameter and duct inlet conditions was Re = 15,000. This CFD study is based on 3-D steady RANS, where the ensemble averaged continuity, compressible Navier-Stokes, and energy equations are closed by the thermally perfect equation of state and the two-equation realizable k-e turbulence model with wall functions and with the low-Reynolds number model of Chen and Patel in the near-wall region. The usefulness of this CFD study was assessed by comparing predicted heat-transfer coefficient and friction factor with available experimental data. Results are presented to show how the flow induced by arrays of pin fins of different heights affects temperature distribution, surface heat transfer, and pressure loss.Copyright © 2011 by ASME

This research aims at developing fan integration technologies to improve the installation loss due to the fan/OGV/strut/pylon interaction of gas-turbine engines for small aircraft on Small Aircraft Project in Japan (the ECO Engine Project). Researches on experimental measurement using fan rig testing and numerical prediction using unsteady CFD analysis are conducted. The UPACS code which is developed by JAXA is used in order to accurately simulate the phenomena which occur in the interaction between a rotating fan and its downstream obstacles like strut/pylon in the fan duct. The accuracy of the CFD simulation is also validated by the measured data acquired in the rig testing. Through the investigations, its interaction mechanisms are clarified and the reducing technologies of such interaction for small aircraft engines are created. In the paper, the achievement of the improved aerodynamic performance by introducing the new concept of the long nose shaped fat pylon L/E are demonstrated.Copyright © 2011 by ASME

CFD simulations were performed to study the flow and heat transfer in a U-duct, relevant to internal cooling of the first-stage turbine component in electric-power-generation, gas-turbine engines. Parameters studied include (1) two aspect ratios of the duct cross section, i.e. H/W = 1 and H/W = 0.25; (2) smooth duct and duct lined with pin fins of height H arranged in a staggered fashion; and (3) two rotational speeds: 0 rpm and 3,600 rpm. In all cases, the wall temperature is 1173 K; the coolant temperature at the U-duct inlet is 623 K; and the back pressure at the exit of the U-duct is 25.17 atm. The Reynolds numbers studied are 150,000 for the duct with the 4-to-1 aspect ratio, and 150,000 and 375,000 for the duct with the 1-to-1 aspect ratio. When there is rotation at 3,600 rpm, the rotational numbers corresponding to these Reynolds numbers and duct aspect ratios are 0.592, 1.64, and 4.11, respectively. Result is presented to show the nature of the flow, the temperature distribution, and the surface heat transfer with focus on the flow and heat transfer in the tip-turn region as a function of the parameters investigated. This computational study is based on 3-D steady RANS. The ensemble-averaged continuity, compressible Navier-Stokes, and energy equations were closed by the thermally perfect equation of state with temperature-dependent gas properties and the two-equation realizeable k-e turbulence model with and without wall functions.Copyright © 2011 by ASME

In a two-dimensional turbulent jet, there exists a lateral vibration of the high-speed jet core. In the present study, a periodic initial disturbance is introduced into fully developed turbulent jet from a slot mounted at a duct exit in order to control this vibration. The streamwise and lateral velocity fluctuations are measured with an anemometer with an X-type probe, and are filtered using a phase ensemble average technique based on the periodic initial disturbance. This vibration enables extraction of the fluctuation of the synchronized disturbance and restruction of its velocity field. The experimental result shows that the streamwise variation of the extracted amplitude draws a characteristic growth curve that has the exponential growth at the upstream and slow decay parts at the downstream. It is worth noticing that within a certain amplitude of the initial disturbance the growth curves are identical as well as the spatial distribution of the extracted fluctuations. Furthermore the disturbance amplitude is directly proportional to the intensity of the initial disturbance. A linear stability theory with parallel flow assumption well captures futures of the lateral disturbance. This apparent linearity of the disturbance keeps until the average velocity and the total velocity fluctuation starts to vary with sufficient amplitude of the disturbance. The existence of the linear mode in the turbulent jet implies that the large-scale disturbance can be regarded as an incoherent set of the linear modes.

This study presents numerical simulations of forced convection with parachute-shaped encapsulated phase-change material particles in water, flowing through a square cross-section duct with top and bottom iso-flux surfaces. The system is inspired by the gas exchange process in the alveolar capillaries between the red blood cells (RBC) and the lung tissue. The numerical model was developed for the motion of elongated encapsulated phase change particles along a channel in a particulate flow where particle diameters are comparable with the channel height. Results of the heat transfer enhancement for the parachute-shaped particles are compared with the circular particles. Results reveal that the key role in heat transfer enhancement is the snugness movement of the particles and the parachute-shaped geometry yields small changes in heat transfer coefficient when compared to the circular ones. The effects of various parameters including particle diameter and volume-fraction, as well as fluid speed, on the heat transfer coefficient is investigated and reported in this paper.Copyright © 2011 by ASME

Since its publication in 1996, ASME PTC 46 Performance Test Code on Overall Plant Performance has established itself as the premier test code for conducting overall plant performance within the power industry, especially for combined cycle power plants. The current text within ASME PTC 46, which is currently under revision by the ASME PTC 46 Committee, describes in Section 5.3.4 Specified Measured Net Power that “This test is conducted for a combined cycle power plant with duct firing or other form of power augmentation, such as steam or water injection when used for that purpose.” Further, the only example problem for a combined cycle with duct firing is provided in Appendix B of the code utilizing the Specified Measured Net Power Test Method. Though the text and example are correctly presented within the code, it resulted in misinterpretation within the industry that the only correct way to test a combined cycle plant with duct firing was to conduct a Specified Measured Net Power Test. Though the Specified Measured Net Power Test Method is an acceptable and accurate method in determining the performance of a combined cycle plant with duct firing in operation, it lends to being inflexible to the weather conditions for the plant operation. When the weather is too cold, the exhaust energy from the combustion turbines may be at such a magnitude as to not allow the duct burners to be fired due to limitations within the heat recovery steam generator and steam turbine systems to take the load, thus limiting the plant testing to take place when the weather is warm enough to allow the plant to be operated with duct firing. The opposite condition can also exist where the ambient conditions are too hot so that the duct burner capacity is unable to achieve the specified measured net power allowing the test to be conducted. The limitations stated herein are the reasons that an alternative approach with more flexibility is necessary. This paper will present an alternative approach referred to as the Fixed Duct Burner Heat Input Test Method to testing combined cycle plants where the duct burner heat input (Fuel Flow) is held fixed while the plant net power and heat rate are left to float with ambient conditions. Corrections for both power and heat rate will be developed for ambient conditions per ASME PTC 46 guidelines. This paper will further present a comparison between the Specified Measured Net Power Test Method and the Fixed Duct Burner Heat Input Test Method in the areas of the flexibility of the methods for various ambient conditions, and the method uncertainty associated with each method’s ability to correct to reference conditions.Copyright © 2011 by ASME

Within gas turbines the ability to design shorter aggressive S-shaped ducts is advantageous from a performance and weight saving perspective. However, current design philosophies tend to treat the S-shaped duct as an isolated component, neglecting the potential advantages of integrating the design with the upstream or downstream components. In this paper such a design concept is numerically developed in which the upstream compressor outlet guide vanes are incorporated into the first bend of the S-shaped duct. Positioning the vane row within the first bend imparts a strong radial gradient to the pressure field within the vane passage. Tangential lean and axial sweep are employed such that the vane geometry is modified to exactly match the resulting inclined static pressure field. The integrated design is experimentally assessed and compared to a conventional non-integrated design on a fully annular low speed test facility incorporating a single stage axial compressor. Several traverse planes are used to gather five-hole probe data which allow the flow structure to be examined through the rotor, outlet guide vane and within the transition ducts. The two designs employ almost identical duct geometry, but integration of the vane row reduces the system length by 21%. Due to successful matching of the static pressure field, the upstream influence of the integrated vane row is minimal and the rotor performance is unchanged. Similarly the flow development within both S-shaped ducts is similar such that the circumferentially averaged profiles at duct exit are almost identical, and the operation of a downstream component would be unaffected. Overall system loss remains nominally unchanged despite the inclusion of lean and sweep and a reduction in system length. Finally, the numerical design predictions show good agreement with the experimental data thereby successfully validating the design process.Copyright © 2011 by Rolls-Royce plc

An assessment of energetic performance achievable by GT inlet air cooling through cold thermal storage is presented. Results have been obtained by a numerical code specifically developed to model the whole system behavior all over a year. Some cases with hot climatic condition have been compared and discussed in order to enlighten performance differences due to GT characteristics and possible enhancement strategies for different configurations. An existing 127 MWe combined cycle power plant with a twin GT configuration was assumed as a reference case. Two heavy-duty units with different technology levels have been compared with an advanced aero-derivative model, in the range of 40 MW power output. Aero-derivative unit provided a much better performance than the more advanced heavy-duty model; this was strictly related to the higher sensitivity to inlet air temperature of the aero derivative unit. The comparison between the two heavy-duty GTs has clearly shown that a high specific power is needed to obtain cost-effective solutions for inlet air cooling systems. The analysis for the considered GT units was then extended also to a plant configuration including an inlet air supercharging system. The boost fan head has been selected in order to only compensate all inlet pressure losses, i.e. inlet duct, filters and air coils pressure drops.Copyright © 2011 by ASME

This work presents a numerical study of a nozzle/diffuser micropump under several frequencies of operation. The investigation focuses on the effects caused by two principal changes in the geometry: 1) a small duct portion included before the nozzle/diffuser element, with the purpose of inducing a fully developed flow, and 2) the size of the fluctuating chamber. As expected, the net flow rate of a nozzle/diffuser micropump increases with pumping frequency and also with the size of the fluctuating chamber. However, the duct before the nozzle/diffuser element causes more losses and a decrement in the net flow, though inducing a better flowing of the fluid into the nozzle.Copyright © 2011 by ASME

Freeze-drying is a low-pressure, low-temperature condensation pumping process widely used in the manufacture of pharmaceuticals for removal of solvents by sublimation. The performance of a freeze-dryer condenser is largely dependent on the vapor and ice dynamics in the low-pressure environment. The main objective of this work is to develop a modeling and computational framework for analysis of vapor flow and ice dynamics in such freeze-dryer condensers. The direct Simulation Monte Carlo (DSMC) technique is applied to model the relevant physical processes that accompany the vapor flow in the condenser chamber. Low-temperature water vapor and nitrogen molecular model is applied in the DSMC solver SMILE to simulate the bulk vapor transport. The developing ice front on the coils of the condenser is tracked based on the steady state mass flux computed at the nodes of the DSMC surface mesh. Verification of ice accretion simulations has been done by comparison with the solution for analytical free-molecular flow over a circular cylinder. The developed model has also been validated with measurements of ice growth in a laboratory and production scale freeze-dryer using time-lapse imaging. To illustrate the application of the ice accretion algorithm in the area of bio-pharmaceutical freeze-drying, the current work discusses the effect of the condenser geometry and non-condensable gas on non-uniformity of mass flux in a laboratory scale and production scale freeze-dryer condenser. In addition, the simulations are used to predict the ice formation on the coils of the condenser. It was found that in the laboratory scale dryer, the presence of a duct connecting the product chamber and condenser increased non-uniformity by 65% at a sublimation rate of 5 g/hr. The measured ice thickness on the coils of the condenser was found to increase non-linearly. This non-linearity was captured within an accuracy of 1% compared to the measurements towards the end of a 24 hour cycle using an unsteady icing model while that using a steady model was within 14%. In the production dryer, while the steady model predicted the iced coil diameter within an accuracy of 2–5% with respect to the measurements, the unsteady model captured this within an accuracy of 1–6%. The DSMC simulations demonstrate that by augmenting its capabilities with the icing model, it is possible to predict the performance of a freeze-dryer condenser with any arbitrary design.

Experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/djet = 3 –6. For p/djet = 3 , cylindrical as well as conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000 ≤ Re ≤ 75,000 . Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low-Re k-ω-SST turbulence model. The results show that for greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer. The area averaged Nusselt numbers decrease by up to 15% for p/djet = 4.5 , and up to 30% for p/djet = 6 , respectively, if compared to the baseline pitch of p/djet = 3 . The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.Copyright © 2011 by ASME and Alstom Technology, Ltd.

For nuclear power plant life extension projects, it may be convenient and in some instances necessary to locate safety-related steel ducts and pipes outside of the main structures, exposing them to extreme environmental loads such as tornado missile impact. Examples of such applications include emergency firewater lines and Control Room vent ducts. The design of a tornado-impacted duct or pipe system requires an estimate of its dynamic response and an establishment of damage limits. These considerations are complicated by the system geometric and material nonlinearities and the local triaxiality effects on the response ductility limit. Simple, but acceptable accurate techniques for comprehensive evaluation of steel ducts under impact loads have not been established. This study presents simplified evaluation techniques for a steel duct/pipe under a heavy impact load, using fundamental concepts. The approach presented could be utilized to evaluate steel ducts/pipes against not only tornado missile impact loadings, but other types of transient loads as well. Both local and global responses of duct/pipe lines under missile impacts are evaluated. Applied impulse loadings for various types of tornado missiles are first established. A non-linear pseudo-static finite element analysis is performed in lieu of a more complicated dynamic analysis. The result is adopted for evaluation of the local ductility of ducts and pipes by using triaxial strain criteria. Global ductility and global shear checks are performed based on inelastic single-degree-of-freedom analysis methods. Pipe line design diameters and thicknesses are then determined based on the local ductility, global ductility and global shear evaluations. Accuracy of the non-linear pseudostatic analysis is discussed and a practical example using the proposed methodology is presented.

Large-eddy simulation (LES) using wall-adapting local eddy-viscosity (WALE) subgrid scale model has been applied towards elucidating the complex turbulent flow physics in a centrifugal impeller. Several canonical cases of increased complexity were analyzed to better understand the advantages and challenges of applying the LES framework to the aforementioned target problem. These include turbulent flow in a rotating channel, a straight and a curved duct. Results obtained with LES are compared in detail with two-equation eddy-viscosity Reynolds Averaged Navier-Stokes (RANS) turbulence models widely used in industry, as well as, for some of the canonical cases, with hybrid RANS/LES approaches such as the detached eddy simulation (DES) and scale-adaptive simulation (SAS). Finally, LES has been applied to turbulent flow in NASA CC3 centrifugal impeller with grids of increased resolution (up to 100 million computational cells per passage).

This paper focuses on the application of CFD to turbocharger compressor characteristics predictions over a range of speeds between 100,000 and 200,000RPM, and concentrating around the peak performance at 160,000RPM. A production turbocharger compressor which is widely used in the small-to-medium size automotive sector is studied. A methodical approach is taken to compare computation versus rig measurements, which represents an idealised installation. Benchmarking under the idealised rig conditions then gives a degree of confidence to apply the same prediction method to the device under real installation conditions. In practice this means that the inlet duct is strongly curved due to space constraints. One observes that the performance of the compressor deteriorates at higher mass flows when the inflow to the compressor face is distorted by a curvilinear duct. Under the same installation constraint, we then observe that performance reduces when using inlet guide vanes upstream of the compressor face to alleviate noise problems. A primary motivator in this work is to develop an efficient methodology for analysing the turbocharger compressor performance. To do this it is necessary first to benchmark the CFD methodology in steady-state so that the OEM can be confident to perform intake design analyses for their vehicles under installation conditions. Therefore we concentrate here on robust processes for geometry handling, meshing and flow solution which can be easily automated.Copyright © 2011 by ASME

Knowledge of cap-bubbly flows is of great interest due to its role in understanding of flow regime transition from bubbly to slug or churn-turbulent flow. One of the key characteristics of such flows is the existence of bubbles in different sizes and shapes associated with their distinctive dynamic natures. This important feature is, however, generally not well captured by available two-phase flow models. In view of this, a modified two-fluid model, namely a three-field two-fluid model, is proposed. In this model, bubbles are categorized into two groups, i.e., spherical/distorted bubbles as Group-1 while cap/churn-turbulent bubbles as Group-2. A two-group interfacial area transport equation (IATE) is implemented to describe the dynamic changes of interfacial structure in each group, resulting from intra- and inter-group interactions and phase changes due to evaporation and condensation. Attention is also paid to the appropriate constitutive relations of the interfacial transfers due to mechanical and thermal non-equilibrium between different fields. The proposed three-field two-fluid model is used to predict the phase distributions of adiabatic air-water flows in a narrow rectangular duct. Good agreement between the simulation results from the proposed model and relevant experimental data indicates that the proposed model may be used as a reliable computational tool for two-phase flow simulations in narrow rectangular flow geometry.Copyright © 2011 by ASME

Modern, high-performance, outboard marine engines operate in severe environments. They are typically mounted to a planing boat operating at high horsepower levels due to high hydrodynamic drag. The engine also experiences high vertical impact loads in rough-water conditions. In the ocean, corrosive salt water circulates through the engine to provide necessary engine cooling. Splashing water can be ingested into the combustion air inlets on the outside of the engine cowl (engine enclosure) and must be appropriately managed. In addition, the engine often operates in very warm climates with a sealed cowl wrapped tightly around it. The warm atmospheric air that flows through the cowl inlets and into the engine compartment must first circulate around the power head in order to cool thermally sensitive components such as engine controllers and ignition coils. In some applications, the same air stream mixes with fuel then participates in the combustion process inside the cylinder. At Mercury Marine, computational fluid dynamics, CFD, is used to aid the design of outboard engines that will operate robustly in these extreme conditions. One specific application for CFD is the management of the flow and thermal aspects of engine-compartment air flow. Studies can be done with CFD to assist product design decisions that aim to balance the need to protect thermally sensitive electronics and to efficiently provide the engine with the combustion air. The CFD simulation predicts the air flow behavior from the cowl duct inlets, around the power-head, and into the throttle body inlet of the engine. The simulation also predicts air temperatures, component temperatures, and heat flow to and from the air. The CFD model typically includes rotating components such as alternators and flywheels. A recent study was conducted to validate the CFD method. The CFD model and the dynamometer experiments were conducted with a mid-size outboard 4-stroke engine. The test engine was fully instrumented to measure air temperatures, air velocities, and component temperatures. The validation exercise included a detailed comparison of these values between the CFD predictions and the experimental results. A high level of agreement was achieved and a few lessons were captured for future implementation.Copyright © 2011 by ASME

This paper presents the application of phase averaging to experimental data obtained during scale model testing of a forward facing bent duct oscillating water column (OWC). Phase averaging is applied to both wave probe data and a two-dimensional velocity field at the centerline plane of the OWC model obtained using particle imaging velocimetry (PIV). Results are presented for one monochromatic wave condition. The influence of varied wave frequency is briefly discussed.

The mixing of fuel and oxidizer is critical for the reduction of NOx emissions from premixed combustion burners. The mixing process in a pre-mixer of a natural gas-fired conical wire-mesh duct burner (DB) was studied experimentally using the laser sheet illumination (LSI) technique. A quasi-quantitative technique was used to rank the relative mixing performance of the different geometrical and flow combinations tested (mixer geometry, fuel injection angle and fuel air momentum ratio). The present paper presents some of the results used in the design and analysis of the burner. This burner was integrated and tested with a micro-turbine cogeneration system (MT70 kW Ingersoll Rand (IR) CHP unit). The DB provides supplementary firing in the exhaust gas stream of the microturbine to increase and control the thermal output of the micro-cogeneration system. The combination provided near perfect premixing and low emissions. The DB successfully raised the micro-turbine exhaust gas temperature from about 227°C to as high as 700°C with NOx and CO emissions of less than 5 ppm and 10 ppmv (corrected to 15 percent O2) respectively. The DB also displayed stable, low emissions operation throughout the surface firing rate range of 148 kW to 328 kW (1574 kW/m2 to 3489 kw/m2). The results show that LSI technique can provide invaluable information about the overall flow field structure. Many important observations are discussed such as mixing, fuel spread, and fuel jet penetration. Samples of the LSI images and 3D plots for selected cases are presented. The two best geometrical combinations ranked during the LSI test were used in the actual combustion test of the DB. Some of the combustion results which prove the effectiveness of the LSI technique are presented.

The design of flashback-resistant premixed burners for hydrogen-rich fuels is strongly dependent on reliable turbulent boundary layer flashback limits, since this process can be the dominant failure type for mixtures with high burning velocities. So far, the flashback data published in literature is based on tube burner experiments with unconfined flames. However, this flame configuration may not be representative for the most critical design case, which is a flame being already present inside the duct geometry. In order to shed light on this potential misconception, boundary layer flashback limits have been measured for unconfined and confined flames in fully premixed hydrogen-air mixtures at atmospheric conditions. Two duct geometries were considered, a tube burner and a quasi-2D turbulent channel flow. Furthermore, two confined flame holding configurations were realized, a small backward-facing step inside the duct and a ceramic tile at high temperature, which was mounted flush with the duct wall. While the measured flashback limits for unconfined tube burner flames compare well with literature results, a confinement of the stable flame leads to a shift of the flashback limits towards higher critical velocity gradients, which are in good agreement between the tube burner and the quasi-2D channel setup. The underestimation of flashback propensity resulting from unconfined tube burner experiments emerges from the physical situation at the burner rim. Heat loss from the flame to the wall results in a quenching gap, which causes a radial leakage flow of fresh gases. This flow in turn tends to increase the quenching distance, since it constitutes an additional convective heat loss. On the one hand, the quenching gap reduces the local adverse pressure gradient on the boundary layer. On the other hand, the flame base is pushed outward, which deters the flame from entering the boundary layer region inside the duct. The flashback limits of confined flames stabilized at backward-facing steps followed this interpretation, and experiments with a flush ceramic flame holder constituted the upper limit of flashback propensity. It is concluded that the distribution of the flame backpressure and the flame position itself are key parameters for the determination of meaningful turbulent boundary layer flashback limits. For a conservative design path, the present results obtained from confined flames should be considered instead of unconfined tube burner values.Copyright © 2011 by ASME

The present paper concerns the development and validation of an Eulerian multiphase boiling model to predict boiling and critical heat flux within the general-purpose computational fluid dynamics (CFD) solver FLUENT. The governing equations solved are generalized phase continuity, momentum and energy equations. Turbulence effects are accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model, developed in Rensselaer Polytechnic Institute (RPI). Modifications have been introduced to the quenching heat flux model to achieve mesh-independent solutions. The influences of boiling model parameters have also been systematically investigated. To model non-equilibrium boiling and critical heat flux, the PRI model is extended to the departure from nucleate boiling (DNB) by partitioning wall heat flux to both liquid and vapor phases and considering the existence of thin liquid wall film. Topological functions are introduced to consider the wall boiling regime transition from the nucleate boiling to critical heat flux (CHF), and the corresponding flow regime change from bubbly flows to mist flows. A range of sub-models are implemented to model the interfacial momentum, mass and heat transfer and turbulence-bubble interactions. To validate the Eulerian multiphase boiling model, it has been used to predict nucleating boiling and critical heat flux in a range of 2D and 3D boiling flows. The examples presented in the paper include: (1). Nucleate boiling of sub-cooled water in an upward heated pipe; (2) R113 liquid flows through a vertical annulus with internal heated walls; (3). 3D boiling flows in a rectangular-sectioned duct; and (4). Critical heat flux and post dryout in vertical pipes. The results demonstrate that the model is able to predict reasonably well the distributions of wall temperature, the bulk fluid sub-cooling temperature and cross-sectional averaged vapor volume fraction in the vertical pipe. The computed profiles of the vapor volume fraction, liquid temperature, and the liquid and vapor velocity profiles are generally in good agreement with available experiments in the 2D annular case. In the 3D rectangular duct, the cross-sectional averaged vapor volume fractions are well captured in all the ten cases under investigation. In the case of critical heat flux and post dryout, the model is also able to predict reasonably well the location and the temperature rise under critical heat flux conditions. The computed wall temperature distributions along the pipes are in overall good agreement with available experiments.Copyright © 2011 by ASME

An interface tracking method for predicting motions of bubbles contaminated with soluble surfactants is presented. A level set method is utilized to track the interface. Transportations of surfactants in the bulk liquid and those at the interface are taken into account. The amount of adsorption and desorption is evaluated by using the Frumkin & Levich model. Simulations of bubbles contaminated with soluble surfactants are carried out, i.e., single air bubbles rising through stagnant water, Taylor bubbles in a vertical pipe filled with water, and a wobbling bubble in a vertical duct. As a result, the following conclusions are obtained: (1) the increase in drag coefficients of spherical bubbles due to the presence of surfactant, i.e. Marangoni effect, is well predicted, (2) surfactants mainly accumulate at the rear edge of a Taylor bubble and the Marangoni effect is very small in the nose region at high Eotvos and low Morton numbers, and therefore, the effects of surfactant on the bubble rising velocity are small in low viscosity systems, and (3) the surfactant concentration is low in the top region of a wobbling bubble, whereas it is high in the bottom region. The peak concentration appears at the side edge of the bubble and the location of the peak concentration moves with the bubble and wake movements.Copyright © 2011 by JSME

HAYNES® 242® alloy, based primarily on the Ni-25Mo-8Cr system, derives its low thermal expansion characteristics from its composition and its high strength concomitant with high ductility from a long-range ordering reaction upon an aging heat treatment. This combination has enabled the alloy continually to find a challenging range of applications in the aerospace industry at up to 1300°F (704°C). These include seal rings, containment rings, duct segments, casings, rocket nozzles, etc. In conjunction with the creep strength and environmental resistance, the low cycle fatigue (LCF) behavior is an important material property affecting the service life of 242 alloy components. The low cycle fatigue behavior of 242 alloy was studied under fully reversed strain-controlled mode at 800°F (427°C), 1000°F (538°C), 1200°F (649°C) and 1400°F (760°C) using a triangular wave form with a frequency of 0.33 Hz. Results are presented in terms of cycles to crack initiation and failure. The magnitudes of fatigue lives at total strain range ≤ 0.7% at 800, 1000 and 1200°F are significantly greater than those of solid solution strengthened alloys. Additionally, stress-controlled LCF tests were performed at 1200°F (649°C) on 242 alloy as well as 909 alloy (for comparison). The paper will discuss the results of these two test programs.Copyright © 2011 by ASME

High spatial and temporal resolutions are required in velocity measurements for turbulent flows to examine turbulence characteristics accurately. In this study, we proposed a spatial filter velocimetry (SFV) based on a frequency analysis of time-series spatially-filtered particle images. Since this method can measure velocity from one particle in a measurement region, it enables us to measure the velocity with high spatial and temporal resolutions. We developed a SFV system and applied it to laminar and turbulent flows in a duct to examine its performance. Through comparisons between the velocities measured by SFV and LDV, we confirmed that SFV accurately measures the mean velocity and turbulent intensity with spatial and temporal resolutions as high as LDV.Copyright © 2011 by JSME

IHI has succeeded in development of a new generation Automated People Mover (APM). One of the features of this APM is the composite car body which enables stylish exterior, spacious cabin and light weight. This feature demanded the development of a new Heating, Ventilating, and Air-Conditioning (HVAC) system, which does not have any devices on the roof of the car, to avoid heavy weight on the composite body and to keep the cabin ceiling high for passenger comfort. Consequently we adopted a new HVAC flow system in which the air is supplied upwards from the bottom of the side windows while all the mechanical devices are placed under the floor. However, when the prototype was first designed, it caused congested flow channel due to its location and we had to have ducts that were too small. It was unexpectedly difficult to keep the space for HVAC system like in an ordinary layout. So at first, the prototype vehicle did not have enough HVAC performance due to lack of air flow. Therefore we performed full review of the duct system. We made desk analysis, duct model test, experiment on the prototype, and CFD simulation, for the improvement of the new HVAC flow system. Finally, we have established an excellent system with the new layout which has been validated on the prototype vehicle. In this paper, we describe the process of developing a new HVAC system, based on the results of actual measurement as well as CFD simulation.Copyright © 2011 by JSME

The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the horizontal condensing surface (316 stainless steel) which is the bottom surface (wall) of a rectangular cross-section duct of 2 mm height, 15 mm width, and 1 m length. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or exit) pressure, and wall cooling conditions. Earlier it has been reported that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or exit) pressure, and wall cooling condition held at steady values, there is a very strong sensitivity to certain impositions of pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these certain impositions, it was found that the mean exit (or inlet) pressure changes to significantly affect mean test-section pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).

Transient characteristics as well as unsteady cascade flow fields of a three-stage axial flow compressor with compression plane wave injection from the compressor downstream were experimentally investigated by detail measurements of casing wall pressure fluctuations and unsteady velocity. The main feature of tested compressor is a shock tube facility connected in series to the compressor outlet duct in order to supply a compression plane wave which simulates the sudden rise of the compressor back pressure in a gas turbine system. Research attention is mainly focused on the unsteady behavior of surge and rotating stall coexistence phenomenon, and influence of the compression plane wave injection on the compressor operating conditions. When the compressor is connected to the capacity tank, surge and rotating stall occur simultaneously according to the capacitance increment of the whole compression system. The surge cycle changes irregularly with a throttling of the valve installed just behind the compressor and several different types of surge behaviors are observed. Furthermore, even though the compressor is operating under the stable condition, it goes into surge by injecting the compression plane wave.Copyright © 2011 by JSME

The Power, Water Extraction, and Refrigeration (PoWER) engine has been investigated for several years as a distributed energy system, among other applications, for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semi-closed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, less emission, air, and exhaust flows (which decrease filtration and duct size) and condensation of fresh water. The present paper describes the preliminary design and modeling of a modified version of this system as applied to distributed energy, especially useful in regions which are prone to major grid interruptions due to hurricanes, under - capacity, or terrorism. In such cases, the distributed energy system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is limited in scope. This paper describes the rather straightforward system modifications necessary for ice production. The primary focus of the paper is the use of this ice-making capacity to achieve significant load-leveling during the summer utility peak, hence reducing the electrical capacity requirements for the grid as well as load-leveling strategies.Copyright © 2010 by ASME

Acoustic measurements within combustion chambers are expensive due to high thermal loads applied on the measurement devices at operating conditions. As a more feasible substitute, pressure ducts can be used to lead acoustic waves from combustion chambers to externally mounted microphones. Since these pressure ducts are purged by nitrogen at atmospheric temperature, high thermal loads are avoided. However, the acoustic signal measured within the pressure ducts is altered compared to the signal within the combustion chamber. This change in the acoustic signal can be characterised by means of the acoustic transfer function of the pressure duct, which mainly depends on the pressure ducts geometry and the combustion chambers temperature distribution. The main subject of the present paper is to analyse the influence of the combustion chambers temperature distribution on the acoustic transfer function of pressure ducts. For this scope, experiments at standard conditions and transient CFD simulations for different temperature distributions have been carried out. The acoustic signal measured in the pressure duct is found to be amplified with increasing temperatures within the combustion chamber. Moreover this amplification grows with increasing frequency of the acoustic signals.Copyright © 2010 by ASME

This report presents the design and operation of an accelerated testing facility for the study of deposition in turbine nozzle guide vanes (NGV). The facility was designed to produce turbine deposits in a 1–2 hour test that simulates thousands of hours of turbine operation. This is accomplished by matching the net foreign particulate throughput of an actual gas turbine. The facility seeds a combusting (natural gas) flow with 10–20 micron diameter coal ash particulate. The particulate-laden combustor exhaust is accelerated through a rectangular-to-annular transition duct and expands to ambient pressure through an NGV annular sector. The cascade contains two NGV doublets (donated from industry) comprising three full passages and two half passages of flow. The inlet Mach number (0.1) and gas temperature (1000 °C) are representative of operating power turbines. The vanes are film cooled from an auxiliary air supply at nominal design operating conditions. Investigations over a range of inlet gas temperatures showed that deposition increased substantially with temperature, with a threshold for deposition occurring between 900 °C and 1000 °C. Qualitative test validation was achieved using direct comparison with deposits from service hardware. Surface topography analysis indicated that the surface structure of the generated deposits were similar to those found on actual turbine blades. Regions of heightened deposition were noted; the leading edge and pressure surface being particularly implicated. Film cooling is shown to provide substantial protection from deposition.Copyright © 2010 by ASME

A compressor blade failure was experienced at the 69 MW gas turbine of a combined cycle (C.C.) unit after four years operation since the last overhaul (January 2005). The unit accumulated 27,000 service hours and 97 start-ups since the last overhaul. This unit consists of four gas turbine stages and 19 compressor stages and operates at 3600 rpm. In 2006, the unit was equipped with a fogging system at the compressor air inlet duct to increment unit power output during high ambient temperature days (hot days). These fog water nozzles were installed upstream of the compressor inlet air filter without any water filter/catcher before the water spray nozzles. Three unit failure events occurred at small periods, which caused forced outage. The first failure occurred in December 2008, a second event in March 2009 and the third event in May 2009. Visual examination carried out after the first failure event indicated that the compressor vanes (diaphragms) had cracks in their airfoils initiating at blade tenons welded to the diaphragm outer shroud at stages 3, 8, 9, 10 and 11. Also, many stationary vanes and moving blades at each stage of the compressor showed foreign object damage (FOD) and fractures at the airfoil. Visual examination performed for the second failure event after 60 unit operation hours indicated that many compressor vanes (diaphragms) and moving blades had FOD at the airfoil. This was attributed to fractures of the fogging system water spray nozzle, which were then induced to the compressor flow path channel at high velocity causing the above-mentioned damage. Visual examination completed upon the third failure event after two unit startup attempts indicated damage of compressor stationary vanes and moving blades principally at stages 12 to 16, and also stages 17 to 19. The damage consisted of airfoil fracture in stationary vanes and moving blades, FOD, moving blade tip rubbing, and bending of stationary vanes, moving blades and diaphragm shrouds. A laboratory evaluation of stationary vane tenon fracture indicated a high cycle fatigue (HCF) failure mechanism, and crack initiation was accelerated by corrosion picks on blade surfaces due to high humidity air generated by the fogging system. Stationary vane damage was caused by a rotating stall phenomenon, which generates vibratory stresses in stationary vanes and moving blades during unit start-ups. During the third failure event, stationary vane HCF damage was highly accelerated due to pre-existent partial fractures in tenons generated during previous failure events, which had not been detected by non-destructive tests. Stationary vane and moving blade failure was also influenced by high tenon brittleness in stationary vanes and moving blades generated during manufacture by welding (diaphragms) and repair welding (moving blades) without adequate post-weld heat treatment (stress relieving). A compressor stationary vane and moving blade failure evaluation was completed. This investigation included cracked blade metallographic analysis, unit operation parameter analysis, history-of-events analysis, and crack initiation and propagation analysis. This paper provides an overview of the compressor failure investigation, which led to identification of the HCF failure mechanism generated by rotating stall during unit start-ups, highly accelerated by corrosion generated by the fogging system and influenced by high stationary vane and moving blade brittleness as the primary contribution to the observed failure.Copyright © 2010 by ASME

This paper investigates the non-reacting aerodynamic flow characteristics in Lean Direct Injection (LDI) combustors. The RANS modeling is used to simulate the turbulent, non-reacting, and confined flow field associated with a single-element and a nine-element LDI combustor. The results obtained from the simulation are compared with some experimental data available in literature. The numerical model, which is in accordance with an experimental combustor, consists of an air swirler with 6 helical axial vanes of 60 degree vane angle and a converging-diverging duct, extending in a square flame tube. The numerical model covers the entire flow passage, including the highly swirling flow passage through the swirler vanes, and the combustion chamber. Simulation has been performed with a low Reynolds number realizable k-e model and a Reynolds stress turbulence model. It is observed that the computational model is able to predict the central re-circulation zones (CTRZ), the corner recirculation zones, and the complex flow field associated with the adjacent swirlers with reasonable accuracy. The computed velocity components for the single-element case show that the flow field is similar to the experimental observations.Copyright © 2010 by ASME

The paper is focused on the numerical analysis of a wave topping unit used in a small turbojet engine. The analysis focuses on a four-port reverse flow (RF) wave rotor. The special feature of the considered wave rotor is its very high rotational speed. The wave rotor is connected directly with the common shaft between compressor and turbine, thus, the effects of Coriolis accelerations become important. In this study, first a one-dimensional model is used to estimate geometry of the wave rotor and port timings. Then, multi-dimensional analysis models are employed to predict the different flow characteristics inside the wave rotor channels. Three-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified.Copyright © 2010 by ASME

This paper considers the effect of an upstream compressor stage on a compressor inter-spool duct. The duct geometry must be fixed early in the engine design process, well before the design of the upstream stages. It is therefore important that the designer has a good physical insight into how engine representative inlet conditions affect the limits of the duct design space. An experimental and computational investigation of two strutted inter-spool S-ducts was undertaken. Both were tested with and without an upstream stage present. The first duct is of a conventional axisymmetric design with a radius change to length ratio ΔR/L = 0.50. This duct is characteristic of the most extreme ducts considered in modern engine design. The second duct is of a non-axisymmetric design and is 20% shorter, ΔR/L = 0.625. This is well beyond the design limit of axi-symmetric strutted ducts. The paper shows that the presence of the upstream stage increases the duct loss by 54%. The rise in loss occurs on the hub wall and is the result of the incoming stator wakes pooling onto the hub wall, forming a row of contra-rotating streamwise vortex pairs adjacent to the hub wall. These vortices pump boundary layer fluid into the free stream, thus raising the mixing loss. In the non-axisymmetric duct an extra mechanism was observed. The streamwise vortex pairs act to ‘re-energise’ the boundary layer. This reduces strut secondary losses caused by the endwall contouring. The net result is that on the non-axisymmetric duct the presence of an upstream stage only increases the duct loss by 28%. Comparing the two ducts, it is shown that with engine representative inlet conditions, the conventional symmetric duct and 20% shorter non-axisymmetric duct have identical performance. This shows that low loss ducts can be designed which are significantly more extreme than current design limits.Copyright © 2010 by ASME

This study presents an investigation of the impact of filleted edge variations on heat transfer. In real gas turbines, sharp edges are an approximation because of manufacturing tolerances and/or geometrical modifications occurring during operation. The value of fillet radius is not exactly known a priori. It can be assumed that a specific radius occurs with a probability following a probabilistic distribution. For this reason, the effect of variation of the filleted edge on internal channel of a film cooling configuration has been studied numerically using an in house solver. The hole exit is fanshaped and the feeding duct axis and the main stream are perpendicular to each other. A response surface has been generated, varying the internal Mach number of coolant and the pressure ratio range between coolant and main gas. Four fillet radii for the internal duct have been analyzed, r/D=0.0–5%. A Gaussian distribution for the fillet radius has been assumed. Using the overmentioned distributions, it is possible to obtain the probabilistic functions of corresponding discharge coefficient Cd and adiabatic effectiveness η. The overall variation of Cd and η can be more than 10% the value without fillet. Furthermore, the differences on Cd due to the uncertainties on fillet radius are bigger than those obtained due to modifying the exit duct shape (i.e., from cylindrical to fanshaped). This paper shows that the effect of variation of fillet radii must be included in numerical simulations. This has direct consequences on LES and DNS simulations, which normally include sharp corners or mean radii. A probabilistic approach must be included in the analysis of the results and the equivalent fillet radius must be assumed instead.

Thermo-acoustic instabilities in lean gas turbine combustors have been well reported over the past decade. One option by which the generation of potentially damaging, large scale, pressure amplitudes can be avoided is to increase the amount of damping within the combustion system using passive damping devices. Common to these devices is the absorption mechanism by which acoustic energy, associated with incident pressure fluctuations onto an orifice, generates an unsteady flow that cannot be converted back into acoustic energy. This paper is concerned with providing a greater understanding of this fundamental process. Experimental results are presented for a single orifice that is exposed to plane acoustic waves within a rectangular duct. Measurements of unsteady pressure enable the acoustic power absorbed by the orifice to be determined, whilst Particle Image Velocimetry (PIV) is used to measure the unsteady flow field. A method is outlined for identifying those features within the measured unsteady flow field that are responsible for absorption of the acoustic energy. This is based on a Proper Orthogonal Decomposition (POD) analysis of the velocity field and identification of the relevant modes. The method is validated for the non-linear and linear absorption regimes by comparing the energy of the relevant velocity field features with the energy absorbed from the acoustic field. The good agreement obtained indicates the success of the technique presented. The improved understanding of the mechanisms by which energy is transferred out of the acoustic field, and into the unsteady velocity field, explains many of the observed absorption characteristics. This improved understanding should lead to the design of optimized damping systems. The presented methodology is also thought to be the basis by which numerical, CFD based, predictions relating to the absorption of acoustic waves should be analyzed and validated.Copyright © 2010 by Rolls-Royce plc

The occurrence of combustion instability dynamics known, as “screech, howl and growl,” in the combustors of gas turbine engines is a very difficult challenge for engineers. The very high amplitude pressure oscillations caused by combustion dynamics, are not only detrimental to the operation of the engine and combustor, but the difficulty in predicting and remedying these problems can lead to significant costs and delays in engine development. The coupling of the unsteady heat release in the flame with the natural acoustic resonance modes of the combustor duct causes the phenomena of combustion dynamics. To improve our understanding of stability characteristics in such complex systems, encountered in many industrial applications, the flame structure of an atmospheric swirl-stabilized burner, containing dilution and cooling air holes and fed with natural gas fuel, was systematically investigated for various inlet temperatures, pressure drops and air-fuel ratios. Experiments were also designed and conducted with the goal to understand better the phenomena of combustion dynamics that were experienced. More specifically, six acoustic pressure transducers were incorporated in the combustor and in the upstream duct to measure the acoustic field and the acoustic impedance characteristics at specified locations of interest. A one-dimensional wave propagation model is presented to predict the acoustic frequencies and damping of resonance modes, based on the geometry of the test rig, the flow conditions, and the acoustic impedance characteristics of the terminations of the combustor. This paper will present the acoustic analysis of the test data in the light of the above-mentioned theoretical modeling. The limitations of the current test rig are pointed out and changes in the rig design are discussed for future research.Copyright © 2010 by ASME

The impact of wet compression technology on compressor performance is studied using a coupled water-evaporation-pitch-line numerical model. The model uses an iterative approach to compute the modified flow conditions at blade-row stations due to inter-stage evaporation of water droplets introduced at the compressor inlet. The evaporation rate predicted by the model is compared with experimental data for stationary droplets in a duct. Performance predictions are compared with data for a GE-proprietary compressor. Study of various water droplet sizes and various water-to-air mass ratios is discussed.Copyright © 2010 by ASME

The temperature of the flow entering a high-pressure turbine stage is inherently non-uniform, as it is produced by several discrete, azimuthally-distributed combustors. In general, however, industrial simulations assume inlet temperature uniformity to simplify the preparation process and reduce computation time. The effects of a non-uniform inlet field on the performance of a commercial, transonic, single-stage, high-pressure, axial turbine with a curved inlet duct have been investigated numerically by performing URANS (Unsteady Reynolds-Averaged Navier-Stokes equations) simulations with the SST (Shear Stress Transport) turbulence model. By adjusting the alignment of the experimentally-based inlet temperature field with respect to the stator vanes, two clocking configurations were generated: an aligned case, in which each hot streak impinged on a vane and a misaligned case, in which each hot streak passed between two vanes. In the aligned configuration, the hot streaks produced higher time-averaged heat load on the vanes and lower heat load on the blades. As the aligned hot streaks impinged on the stator vanes, they also spread spanwise due to the actions of the casing passage vortices and the radial pressure gradient; this resulted in a stream entering the rotor with relatively low temperature variations. The misaligned hot streaks were convected undisturbed past the relatively cool vane section. Relatively high time-averaged enthalpy values were found to occur on the pressure side of the blades in the misaligned configuration. The non-uniformity of the time-averaged enthalpy on the blade surfaces was lower in the aligned configuration. The flow exiting the rotor section was much less non-uniform in the aligned case, but differences in calculated efficiency were not significant.Copyright © 2010 by ASME

This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct. Such duct geometries can be found in many engineering applications where cooling air extracts heat from hot internal walls of the duct, e.g., passage cooling inside gas turbine blades. Both friction factors and convective heat transfer coefficients were measured inside a U-duct for three different cases, namely (a) the smooth straight part, (b) the smooth bend (turn) part, and (c) a rough (ribbed) bend (turn) part. The details of the duct geometry were as follows: the cross section area of the straight part was 50×50 mm2, the inside length of the bend part 240 mm, the cross section area of the rib was 5×5 mm2 and the rib height-to-hydraulic diameter ratio, e/Dh, was 0.1. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configuration can be changed. Both the U-duct and the rib were made from plexiglass material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The rib was placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The friction factor ratio and the heat transfer enhancement ratio for case (c) at a Reynolds number of 20,000 were 48.75 and 2.66, respectively. It is found that the presence of the rib increases the heat transfer coefficient on the outer wall of the bend part (tip of side U-duct). The uncertainties were 3% and 6% for the Nusselt number and friction factor, respectively.

The paper demonstrates the successful application of an optimisation methodology for the design of a diffuser-ejector exhaust duct. Maximising simultaneously pressure recovery and the entrainment ratio are diverging objectives which could hardly be achieved by a conventional manual trial-and-error approach relying on the designer’s experience. This multi-objective design problem has been solved for the axis-symmetric exhaust duct with a given characteristic length, inlet section and minimal standoff distance by coupling a parametric method with 2D CFD analysis. Open cubic B-splines have been employed to generate the contoured duct shape, for which the control-point vertices have been defined by a total of 17 engineering parameters. A bell mouth inlet has been chosen for the ejector inlet. The parameter constraints result from weight and integration requirements. Three characteristic engine operating points have been chosen for the multi-point and multi-objective shape optimisation. The entire process of model building, meshing, performing the 2D CFD calculation and post-processing to extract the required metrics has been fully automated. A commercial process integration software package is used to link the different tools together in a unified environment. The design space exploration is carried out via a latin-hypercube sampling technique. This random space filling method has been chosen because of its considerable lower number of experiments compared to factorial sampling techniques. Parameter ranking is obtained by a weighted average of the correlation coefficients for each objective. The parameter hierarchy is slightly different for the engine operating points. However, there exists a clear threshold separating the influential parameters from the insignificant ones. A subsequent DOE is performed for the reduced parameter set for which the minimum number of experiments has been chosen as twice the number of experiments to generate a quadratic response surface. The Normal-Boundary Intersection method is applied to find the Pareto front based on the response surface model as surrogate model. The results show that a gain of 20% for the pressure recovery for a given entrainment ratio could be achieved compared to a configuration defined by a manual trial-and-error approach. The great benefit of the present method is its capability to handle easily geometrical constraints and the weight of the different design objectives which may change even during the detailed design phase.