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In modern transonic compressors, the forced response can occur thigh-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose ofthis paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, a test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing., QC 20210608

In modern transonic compressors, the forced response can occur thigh-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose ofthis paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, a test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing., QC 20210608

In modern transonic compressors, the forced response can occur thigh-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose ofthis paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, a test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing., QC 20210608

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration, one with the Coriolis force removed, without any other change. This setup allows very clean assessment of the influence of rotation. The turbulenceresolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region the Tip Leakage Vortex is enlarged and destabilised. Inside the tip gap the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly., Funding was provided by the Deutsche Forschungsgemeinschaft (DFG), under FR1593/15-1 and MA4922/8-1 within PAK948. The authors would like to acknowledge stimulating discussions with the partners of this project. Computations were performed at the Centre for Information Services and High Performance Computing (ZIH) at TU Dresden., Postprint (published version)

In modern transonic compressors, the forced response can occur thigh-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose ofthis paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, a test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing., QC 20210608

In modern transonic compressors, the forced response can occur thigh-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose ofthis paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, a test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing., QC 20210608

Linear cascades are commonly used as surrogate geometries when performing fundamental studies of turbomachinery blading. Several effects are not accounted for in linear cascades, among them the relative motion between blade and endwall. In this study three different relative endwall velocities are analysed. The effect of the relative motion between endwall and blade in a linear compressor cascade is studied through Direct Numerical Simulations. Results show a significant change in the secondary flow structure within the passage. Most notably, the tip leakage vortex is displaced away from the blade. Still, the blade spanwise range affected by the secondary flow field is similar to the case without relative endwall motion. At the outlet plane, a stratification of the total pressure losses and the exit flow angle is found, which overshadows any blade wake effects near the endwall., Funding was provided by the Deutsche Forschungsgemeinschaft (DFG), through package proposal PAK948. The authors like to acknowledge stimulating discussions with the partners of this project. Computations were performed at the Centre for Information Services and High Performance Computing (ZIH) at TU Dresden., Postprint (published version)

In the first part of the thesis, we carried out direct two-dimensional (2D) multipoint measurements of the velocity fields in a turbulent Rayleigh-Benard convection cell to study the properties of small-scale convective turbulence. The local homogeneity and isotropy of the velocity field are tested using a number of criteria and are found to hold to an excellent degree. The properties of velocity circulation Gammar are also studied. The results show that the circulation appears to be more effective to capture the effect of local anisotropy than the velocity field itself. The distribution of Gammar is found to depend on the scale r, reflecting strong intermittency. It is further found that velocity circulation has the same anomalous scaling exponents as the longitudinal and transverse structure functions for low-order moments (p ≲ 5). Whereas, for high-order moments (p ≳ 5), the anomalous scaling exponents for circulation are found to be systematically smaller than the scaling exponents of the longitudinal and transverse structure functions., In the second part of the thesis, the simultaneous visualization of the temperature and velocity fields was used to study the properties of thermal plumes. Our visualization reveals the process of the morphological evolution between sheetlike and mushroomlike plumes, which were also quantified by the height dependence of plume numbers and of vorticity fluctuations. A direct connection between the heat transport and coherent structures, i.e. thermal plumes, was established, which shows that it is plume number that primarily determines the Nu-Ra scaling relation. Individual plumes were extracted and their statistical and geometric properties were studied. It is found that the log-normal distribution is universal for thermal plumes and the log-normal statistics may be used to model them. In addition, both our quantitative characteristic and direct 3D spatial visualizations indicate that the previously-believed sheetlike plumes should be reconsidered to be only one-dimensional structures., In the third part of the thesis, the planar laser-induced fluorescence technique was induced to study the 2D passive scalar mixing in high-Schmidt-number buoyancy-driven turbulence. The passive scalar mixing evolution was studied and various geometric properties, such as shape complexity, fractal dimension and local curvature, were used to characterize the isoconcentration contours of the 2D passive scalar fields. It is found that when the flow gets more turbulent the shape of passive scalar packets becomes closer to a circular shape and the passive scalar mixing becomes more isotropic, indicating the increased mixing and stirring of the turbulent flow., The objective of this thesis is to address the following three key issues in turbulent thermal convection, i.e. turbulent fluctuations in small scales, coherent structures and passive scalar mixing in buoyancy-driven turbulence., Zhou, Quan = 對流熱湍流中能量級串, 相干結構和標量場混合的实验研究 / 周全., Adviser: Ke-Qing Xia., Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3576., Thesis (Ph.D.)--Chinese University of Hong Kong, 2008., Includes bibliographical references (leaves 103-117)., Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web., Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web., s in English and Chinese., School code: 1307., Zhou, Quan = Dui liu re tuan liu zhong neng liang ji chuan, xiang gan jie gou he biao liang chang hun he de shi yan yan jiu / Zhou Quan., isbn: 9781109225617, Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981., MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO, Includes bibliographical references., by Saeed Farokhi., Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981., MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO, Includes bibliographical references., by Saeed Farokhi., Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981., MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO, Includes bibliographical references., by Saeed Farokhi., Ph.D.

Summary: The purpose of this research is to study the modification of a turbulent flow as it passes through a cascade of flat plates. The results will then be compared with experimental results obtained in a companion experimental study being conducted at Virginia Tech. In a typical marine propulsor turbulent flow passes through a set of inlet guide vanes (IGVs) and then interacts with the propeller blades: this process creates unwanted vibration and sound. The purpose of this research is to determine if the arrangement of the IGVs can be used to reduce the propulsor noise generation. In this study the incoming flow to the propeller is modeled as homogeneous turbulence and the IGVs are represented by a cascade of flat plates. We will consider the equations, which describe the blade response to an incoming harmonic gust, and we will represent the turbulent flow using a modal description., College of Engineering and Computer Science, Collection: FAU Electronic Theses and Dissertations Collection, Thesis (M.S.)--Florida Atlantic University, 2003.

Summary: The interaction of rotor turbulence with the stator is currently believed to be the predominant mechanism of noise radiation from turbofans in aircraft engines. This thesis presents a general method to compute unsteady 2-D potential flows past a cascade of airfoils. The procedure uses source and vortex distributions on the surface of the airfoils, creation of wakes downstream of the airfoils and non-linear convection of the perturbed flow. These features are designed to satisfy a condition of no-flow through the surface of the airfoils and the Kutta condition at the trailing edge of each of these airfoils. The investigation proves the importance of applying the Kutta condition. It was also shown that an infinite cascade is well approximated by a small number of airfoils and that the non-linear rather than linear convection of vorticity has a large effect on the spectrum of the unsteady lift of an airfoil., College of Engineering and Computer Science, Collection: FAU Electronic Theses and Dissertations Collection, Thesis (M.S.)--Florida Atlantic University, 1998.

Summary: When a boundary-layer flow, either laminar or turbulent, encounters a hemispherical body extending from a surface, a horseshoe-shaped vortex forms at the juncture. In this thesis, we study the evolution of this vortex using a numerical inviscid model and laboratory experiments. The numerical model is based on determining the evolution of the filament using the cut-off method. The assumption is that although the generation of the vortex depends on viscous effects, the dynamic evolution is well described by inviscid equations of motion. It is found that the vortex filament is fairly steady on the upstream side but on the downstream side, travelling waves appear on it which cannot be suppressed through evolution. For a range of Reynolds number, steady horseshoe-shaped vortex was obtained in the experiments, revealing the shape past the hemisphere. This is compared with the numerical results., College of Engineering and Computer Science, Collection: FAU Electronic Theses and Dissertations Collection, Thesis (M.S.)--Florida Atlantic University, 1996.

We examine the dense gas behavior of Bethe-Zel'dovich-Thompson (BZT) fluids in two-dimensional, steady, inviscid, supersonic cascade configurations. Bethe-Zel'dovichThompson fluids are single-phase gases having specific heats so large that the fundamental derivative of gas dynamics, Γ, is negative over a finite range of pressures and temperatures. The equation of state is the well-known Martin-Hou equation, and the numerical scheme is the explicit predictor-corrector method of MacCormack. Numerical comparisons between BZT fluids and more classical fluids such as steam are presented in order to illustrate the possible advantages of using BZT fluids in supersonic cascades. It was found that the natural dynamics of BZT fluids can result in significant reductions in the adverse pressure gradients associated with the collision of compression waves with neighboring turbine blades. A numerical example of an entirely isentropic supersonic cascade flow using a BZT fluid is also presented.

The effects of freestream turbulence on the total pressure and total temperature in the wake of a cooled transonic turbine cascade with heated flow are presented in this thesis. The experiment was conducted in the Virginia Tech Cascade Wind Tunnel. A dual hot wire aspirating probe was used to make high frequency, unsteady total pressure and temperature measurements. The probe design was modified to be used in a high temperature environment. The flow was heated to temperatures exceeding 140°C and the turbine blades were actively cooled using gaseous nitrogen to maintain a gas to blade temperature ratio between 1.3 and 1.4. A turbulence screen was used to change the freestream turbulence from 3.3% to 7.5%. Mean and turbulent total pressure and temperature quantities are presented. The higher freestream turbulence resulted in lower total pressure and total temperature turbulence intensities in the wakes of the turbine blades. The freestream turbulence level had no measurable effect on the blade losses.

A comprehensive study of the flowfield through a two-dimensional cascade of the high pressure turbine blades of a jet engine is presented. The main interest is the measurement and prediction of the mass-averaged total pressure losses. Other experiments, such as flow visualization, are aimed at the validation of the code that was used to obtain the numerical results and also to further knowledge about the details of the loss generation. The experimental studies were carried out on a cascade of eleven blades in a blow-down tunnel. Total pressure measurements were taken upstream of the cascade and also by traversing on downstream planes. The static pressures needed for the mass averaging and the probe bow shock correction were obtained by pressure taps on the cascade tunnel side wall. The static pressure was also measured on the surface of some instrumented blades. Shadowgraph pictures were taken for study of the trailing edge shock structure and for the turbulent transition location. A single-plate interferometer technique was used for density field measurements. The major goal of the numerical studies was the prediction of the mass-averaged total pressure losses, but all other measured quantities were also generated from the computed flowfield. A critical issue was the generation of a proper grid. For the studied type of flow, a non-periodic C-type grid turned out to be the most advantageous. For use in the moderately compressible attached turbulent boundary layer, a Clauser-type eddy viscosity model was developed and tested. In the trailing edge and wake region, the Baldwin-Lomax model was used. Good agreement of calculations and measurements was obtained for the blade surface and cascade tunnel side wall static pressures, the trailing edge shock structure, and the density field. The agreement between the measured and calculated total pressure drop profiles was not quite as good; however, that quantity is known to be difficult to predict accurately. The mass-average

An investigation has been performed of the flow in a supersonic through-flow fan blade cascade. The blade shapes are those of the baseline supersonic through-flow fan (STFF) under investigation at the NASA Lewis Research Center. Measurements were made at an inlet Mach number of 2.36 over a 15° range of incidence. Flowfield wave patterns were recorded using spark shadowgraph photography and steady-state instrumentation was used to measure blade surface pressure distributions and downstream total and static pressure distributions. A two-dimensional LDV system was used to map the downstream flowfield. From these measurements, the integrated loss coefficients are presented as a function of incidence angle along with analysis indicating the source of losses in the STFF cascade. The results are compared with calculations made using a two-dimensional, cell-centered, finite-volume, Navier-Stokes code with upwind options. Good general agreement is found at design conditions, with lesser agreement at off-design conditions. Analysis of the leading edge shock shows that the leading edge radius is a major source of losses in STFF blades. Losses from the leading edge bluntness are convected downstream into the blade wake, and are difficult to distinguish from viscous losses. Shock losses are estimated to account for 70% to 80% of the losses in the STFF cascade.

This investigation was conducted to determine how design variables affect the basic flow characteristics and performance of compressor cascades with stalled flow. The performance of stalled cascades is required for analyzing with computer models stall and post stall behavior of axial flow compressors. In this investigation, the unsteadiness of the stalled flow and the stalled cascade performance as indicated by the blade normal force and total pressure loss were evaluated. The investigation consisted of both experimental and numerical phases. The effects of stagger, angle of attack and Reynolds number were investigated experimentally using a two-dimensional cascade facility. Surface flow visualization, smoke flow visualization, velocity measurements and pressure measurements were used to evaluate the flow. The flow was modeled numerically by solving the Navier-Stokes equations for a cascade of flat plates. All of the results indicate that blade stagger is a key variable in determining the performance of a stalled cascade. The smoke flow visualization revealed that propagating stall occurred for the cascades with staggers of 36.5 and 45 degrees at all angles of attack greater than or equal to the angle of full stall inception. Propagating stall was never observed for the cascade with a 25 degree stagger. The flow in the passages of the 25 degree stagger cascade was characterized by two distinct regions of flow, a potential or inviscid region with no losses and a separated region with high losses. For the two higher stagger cascades, two distinct regions did not exist. The performance data for the cascades were consistent with the qualitative results obtained in the flow visualization. When presented as a function of angle of attack, the performance parameters indicate that the loss curve is steeper, the maximum value of the normal force coefficient is lower, and the maximum normal force occurred at a lower angle of attack for the higher staggered cascades. The numeri

This thesis presents an investigation into the motions of the horseshoe vortices and the passage vortex, within a plane turbine blade cascade. Fluid motion was determined using a tracer gas technique. Ethylene was injected into the pressure-side and suction-side legs of the horseshoe vortex, near the leading edge of the cascade. Ethylene concentrations were determined at two downstream locations using a flame ionization detector. It was found that the pressure-side leg of the horseshoe vortex moved toward the suction side of the passage, starting the formation of the passage vortex, and was distributed throughout the passage vortex. The suction-side leg of the horseshoe vortex convected once around the periphery of the passage vortex before passing the cascade trailing edge. Downstream of the trailing edge, most of the fluid from the suction-side leg diffused into the passage vortex. However, twice as much fluid from the suction-side leg, as opposed to the pressure-side leg, mixed within the blade wake. At a location 40% of the axial chord downstream of the trailing edge, the passage vortex (shown previously to account for 60% of the overall total pressure losses) contained over 65% of the fluids from both legs.

This thesis describes the design and initial testing of a transonic turbine cascade facility. It is specifically concerned with the best way to obtain flow periodicity and repeatability through the cascade by the use of tailboards at the cascade exit. The problem of how to achieve flow periodicity and repeatability has not been completely resolved. An examination of the literature available on transonic turbine cascade testing indicates some researchers use no tailboards, some use a solid tailboard, and still others use a porous tailboard. In this thesis, the flow through the turbine cascade is tested for three different cascade exit configurations; no tailboard, a solid tailboard, and a porous tailboard. The cascade is also tested with the tailboard at different angles, to see what effect the angle of the tailboard has on the flow through the cascade. The data acquisition and flow visualization systems are discussed and some preliminary results are given.

The oil-film surface flow visualization technique was applied to circular arc compressor blades in a solid wall, high aspect ratio cascade for the purpose of describing the transition from corner stall to full blade stall, and the blade surface flow under fully stalled conditions. Photos of the visualizations for three stagger angles are presented and analyzed. A map quantitatively describing the observed boundary layer development at midspan is presented. The most interesting discovery of the work showed the suction surface flow to be essentially two-dimensional, in the geometric sense, preceding and following the transition to a fully separated flow at the leading edge. Corner stall was the observed three-dimensional mechanism prior to full stall. For fully-stalled conditions, the three-dimensional mechanism took the form of recirculating flow regions at the blade ends. Complete separation at the leading edge occurred at lower angles of attack for the higher stagger angles. Special blade oil-flow tests were conducted to evaluate Reynolds number and tip clearance effects on boundary layer development. The experimental work was done as part of a larger research program aimed at measuring and predicting the stalled performance of a compressor cascade.

An experimental investigation of the performance characteristics of a solid wall linear compressor cascade was conducted. The purpose of the experiments was to determine the effects of the blade row configuration parameters stagger and solidity on the pre-and post-stall behavior of the flow in the cascade. Tests were conducted at a solidity of 1.5, and for two stagger angles, 36.4 degrees and 25 degrees. The investigation included the use of high speed motion pictures with smoke flow visualization in the cascade, measurements of the total pressure and velocity of the flow upstream and downstream of the cascade, and measurements of the blade surface pressures. The experiments were conducted for a range of angle of attack from 0 degrees to 45 degrees. To determine the effects of solidity on the pre- and post-stall behavior of the flow in the cascade, the results obtained for the present 1.5 solidity cascade were compared to previous results from the same cascade tested at a solidity of 1.0. The flow in the two cascades was observed to be similar in nature, but the influence of the reduced blade loading in the high solidity cascade was apparent. For the higher solidity cascade, flow losses at low angle of attack were found to be larger, but stalling behavior was delayed.

An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. This measurement technique was verified in a fully-developed turbulent pipe flow; the results show the accuracy of the probe when used in an end-flow orientation at various incidence angles and with a multiple number of angular settings. Traverses with a single hot-wire at mid-span near the blade row exit show very high levels of turbulence locally in the blade wake near the trailing edge which quickly lessen in magnitude downstream. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10% of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The mass-averaged turbulence kinetic energy accounts for 21% of the total pressure loss at this measurement plane.