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Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet (PSJ) for drag reduction for a hemisphere. Firstly, flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3. As PSJ is a kind of unsteady pulsed jet, the shock standoff distance increases initially and then decreases under the control of PSJ, which corresponds to the change of the strength of PSJ. Accordingly, the amount of drag reduction of the hemisphere increases initially and then decreases. It is found that there is a short period of “drag rise” during the formation of PSJ before the drag reduction, which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator (PSJA). Secondly, the effects of five parameters, including exit diameter, discharge energy of PSJA, Mach number, static pressure of incoming flow and angle of attack, on drag reduction of opposing PSJ were studied in detail by using numerical method. It is found that the Maximum Pressure Ratio (MPR) has a significant impact on the average drag reduction for a configuration-determined PSJA. For the configuration selected in this study, the flow field of opposing PSJ shows typical Short Penetration Mode (SPM) in a control cycle of PSJ when the MPR is less than 0.89. However, the flow field shows typical Long Penetration Mode (LPM) at some time when the MPR is bigger than 0.89. Relatively better drag reduction is achieved in this case.

It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension (2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46 (based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single; the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.

Aiming at the problem of silo design, the silo ejector model and ejector function were proposed. The properties of the static pressure matching function were studied. The critical conditions were a...

Purpose Oil-free heat pumps that use the system refrigerant gases as lubricants are preferred for thermal management in future space applications. This study aims to numerically and experimentally investigate the static performance of externally pressurized thrust bearings lubricated with refrigerant gases. Design/methodology/approach The refrigerant gases R22, R410A and CO2 were chosen as the research objects, while N2 was used for comparison. Computational fluid dynamics was used to solve the full 3 D Navier–Stokes equations to determine the load capacity, static stiffness and static pressure distribution in the bearing film. The numerical results were experimentally verified. Findings The results showed that the refrigerant-gas-lubricated thrust bearings had a lower load capacity than the N2-lubricated bearings, but they presented a higher static stiffness when the bearing clearance was less than 9 µm. Compared with the N2-lubricated bearings, the optimal static stiffness of the R22- and CO2-lubricated bearings increased by more than 46% and more than 21%, respectively. The numerical and experimental results indicate that a small bearing clearance would be preferable when designing externally pressurized gas thrust bearings lubricated with the working medium of heat pump systems for space applications. Originality/value The findings of this study can serve as a basis for the further investigation of refrigerant gases as lubricants in heat pump systems, as well as for the future design of such gas bearings in heat pump systems for space applications.

Scramjet engines are one of the most promising hypersonic airbreathing propulsion technologies for robust, efficient, and economical access to space. Multi-objective design optimization has been co...

Real-time detection and control of the isolator shock-train leading edge (STLE) is important to the performance of high-speed air-breathing engines, such as dual-mode scramjets. Typically, the STLE...

The shape of the blade stacking line greatly influences the low-pressure axial-flow fan’s operational efficiency, but there is still no fast and effective way to determine the stacking line’s optimal shape. This paper presents an automatic optimization design procedure for the blade stacking line in the low-pressure axial-flow fan based on the FINE/Design3D™ platform. The procedure combines computational fluid dynamics (CFD), surrogate model method, and genetic algorithm (GA) to execute a secondary optimization on a composite skewed-swept rotor-only axial fan blade. The results show that the static efficiency and the static pressure rise of the optimized fan respectively increase by 3.76 % and 5.82 % without stall margin decrease. The blade shape variation in skew and sweep direction reduces the tip leakage flow loss, improves the blade loading distribution, and contributes to the efficiency increment. This research provides a useful reference for the blade stacking line’s automatic optimization for the axial-flow fan.

Due to the pressure gain combustion characteristics, the rotating detonation combustor (RDC) can enhance thermodynamic cycle efficiency. Therefore, the performance of gas-turbine engine can be further improved with this combustion technology. In the present study, the RDC operation performance with a turbine guide vane (TGV) is experimentally investigated. Hydrogen and air are used as propellants while hydrogen and air mass flow rate are about 16.1 g/s and 500 g/s and the equivalence ratio is about 1.0. A pre-detonator is used to ignite the mixture. High-frequency dynamic pressure transducers and silicon pressure sensors are employed to measure pressure oscillations and static pressure in the combustion chamber. The experimental results show that the steady propagation of rotating detonation wave (RDW) is observed in the combustion chamber and the mean propagation velocity is above 1650 m/s, reaching over 84% of theoretical Chapman-Jouguet detonation velocity. Clockwise and counterclockwise propagation directions of RDW are obtained. For clockwise propagation direction, the static pressure is about 15% higher in the combustor compared with counterclockwise propagation direction, but the RDW dominant frequency is lower. When the oblique shock wave propagates across the TGV, the pressure oscillations reduces significantly. In addition, as the detonation products flow through the TGV, the static pressure drops up to 32% and 43% for clockwise and counterclockwise propagation process respectively.

An experimental study is conducted to advance the understanding of flow physics associated with a boundary-layer ingesting, distributed propulsion system. The influence of incoming boundary-layer t...

Experiments have been carried out to investigate the effect of cowl length variation on performance characteristics of a single expansion ramp nozzle. The performance parameters were estimated for ...

In order to study the influence mechanism of the motion accuracy of the air static pressure guide system, this article combines the internal transmission law of the driving part of the table and the coupling analysis of solid damping and micro-scale gas damping and establishes the stepping motor, ball screw, nut, and motion table. The four-degree-of-freedom operation model was used to study the response simulation and dynamic characteristics of the entire table under the influence of various components. Combined with the damping characteristics extracted from the experiment, the influence mechanism of micro-gap solids and gas damping on the motion accuracy of the air-floating table is analyzed, and the optimal structural scheme that can effectively improve the accuracy and stability is proposed to improve the performance of the air-floating table and ultra-precision machine tools, processing accuracy to solve key technical problems in improving nano-machining accuracy.

This work focuses on the heat flux characteristics of a hypersonic blunt body with a tangential Mach 3 supersonic cooling film. Experiments were carried out with main flow’s Mach numbers of 6, 7, a...

For a deeper understanding of the physical phenomenology of shock-induced panel flutter, a theoretical model for analyzing aeroelastic stability of flexible panels subjected to an oblique shock has been developed. The von Karman large deflection plate theory is used to account for the geometrical nonlinearity, and local first-order piston theory is employed to predict unsteady aerodynamic loading in shock-dominated flows. In order to consider the nonuniform static pressure differentials induced by the shock, we regard the final total displacement of the panel as the superposition of static deformation and dynamic displacement, which is in accord with the actual situation of physicality. The static deformation is obtained by solving the static aeroelastic equation, and then it is introduced into the dynamic aeroelastic equations in the form of the stiffness by the nonlinear induced loading. According to Lyapunov indirect method and the Routh–Hurwitz criterion, a theoretical solution for the aeroelastic stability boundaries of the flexible panel subjected to an oblique shock is derived. The results show that the presence of an impinging shock wave is found to produce panel flutter that is characteristically different from that with the shock-free condition. For a complex aeroelastic system in shock-dominated flows, there exists a game between the static pressure differential and the unsteady dynamic pressure. When the dynamic pressure gains the upper hand, the presence of shock reduces the aeroelastic stability of the panel. In contrast, when the static pressure difference has the upper hand, the presence of shock will enhance stability of the panel. The dimensionless aerodynamic parameter, which is the ratio of the non-dimensional static pressure to the non-dimensional dynamic pressure of the incoming flow, plays a significant role in aeroelastic stability of panels in shock-dominated flows. For different dimensionless aerodynamic parameters, the flutter boundaries will present different characteristics. As this dimensionless aerodynamic parameter increases, the non-dimensional critical flutter dynamic pressure will increase monotonously.

To investigate the influence of real leading-edge manufacturing error on aerodynamic performance of high subsonic compressor blades, a family of leading-edge manufacturing error data were obtained from measured compressor cascades. Considering the limited samples, the leading-edge angle and leading-edge radius distribution forms were evaluated by Shapiro-Wilk test and quantile–quantile plot. Their statistical characteristics provided can be introduced to later related researches. The parameterization design method B-spline and Bezier are adopted to create geometry models with manufacturing error based on leading-edge angle and leading-edge radius. The influence of real manufacturing error is quantified and analyzed by self-developed non-intrusive polynomial chaos and Sobol’ indices. The mechanism of leading-edge manufacturing error on aerodynamic performance is discussed. The results show that the total pressure loss coefficient is sensitive to the leading-edge manufacturing error compared with the static pressure ratio, especially at high incidence. Specifically, manufacturing error of the leading edge will influence the local flow acceleration and subsequently cause fluctuation of the downstream flow. The aerodynamic performance is sensitive to the manufacturing error of leading-edge radius at the design and negative incidences, while it is sensitive to the manufacturing error of leading-edge angle under the operation conditions with high incidences.

The present experimental study focuses on hydrodynamic cavitation in a transparent horizontal convergent-divergent nozzle. In the experimental section, flow first occurs through a nozzle with a half convergent angle of 21° and then a divergent angle of 8° to exit. The static pressure and the flow rate are varied to achieve different cavitation numbers in sheet mode. Pressure fluctuations are measured at three different locations in the test section of the nozzle and analyzed. Images of the cavities at the throat section are captured, and the average cavity length is measured for all cavitation numbers in sheet mode. The cavity dynamics variation with time is analyzed with the help of image captured using a high-speed camera. The study confirms that the cavitation number and average cavity length are exponentially inversely proportional. Pressure fluctuations and their corresponding frequency are obtained for the different stages of cavitation. The experimental findings show that the sheet cavitation stage is the most turbulent and the magnitude of pressure fluctuations gets smaller as the cavity volume increases.

Based on Recursive Radial Basis Function (RRBF) neural network, the Reduced Order Model (ROM) of compressor cascade was established to meet the urgent demand of highly efficient prediction of unsteady aerodynamics performance of turbomachinery. One novel ROM called ASA-RRBF model based on Adaptive Simulated Annealing (ASA) algorithm was developed to enhance the generalization ability of the unsteady ROM. The ROM was verified by predicting the unsteady aerodynamics performance of a highly-loaded compressor cascade. The results show that the RRBF model has higher accuracy in identification of the dimensionless total pressure and dimensionless static pressure of compressor cascade under nonlinear and unsteady conditions, and the model behaves higher stability and computational efficiency. However, for the strong nonlinear characteristics of aerodynamic parameters, the RRBF model presents lower accuracy. Additionally, the RRBF model predicts with a large error in the identification of aerodynamic parameters under linear and unsteady conditions. For ASA-RRBF, by introducing a small-amplitude and high-frequency sinusoidal signal as validation sample, the width of the basis function of the RRBF model is optimized to improve the generalization ability of the ROM under linear unsteady conditions. Besides, this model improves the predicting accuracy of dimensionless static pressure which has strong nonlinear characteristics. The ASA-RRBF model has higher prediction accuracy than RRBF model without significantly increasing the total time consumption. This novel model can predict the linear hysteresis of dimensionless static pressure happened in the harmonic condition, but it cannot accurately predict the beat frequency of dimensionless total pressure.

The windage loss caused by protrusion in a rotor–stator cavity has been studied in detail, and there are abundant fitting formulas that have been summarized to calculate the moment coefficients. Some other theorists have emphasized its effect on the sealing efficiency, proposing that installation of protrusion could alleviate gas ingestion. However, the protrusion shape which is an influential factor on the sealing efficiency has not been focused in previous research. Using the experimental method of measuring CO2 volume fraction, cavity pressure, and power consumption, we investigated the effects of several typical protrusion shapes on various parameters for two sealing structures, in order to obtain the optimal shape. Results showed that a variation of the protrusion shape had little impact on the static pressure, but the total pressure and the sealing efficiency increased in different degrees. Furthermore, even though the hexagon shape resulted in the highest sealing efficiency, we observed that the drop shape had the best overall performance in all of the eight models, which could result in higher efficiency of the turbine cavity. The combination of a radial seal structure and protrusion could improve sealing efficiency better.

A surrogate-model-based design optimization methodology using Genetic Algorithm to maximize the Static Pressure Rise (SPR) in conical draft tubes is presented. A set of accurate and computationally intensive data obtained from ANSYS-CFD simulations on space filling samples is used for developing a surrogate model. The methodology uses (i) A Latin hypercube experimental design for selecting space filling samples, (ii) Genetic Algorithm for determining parameters of a radial basis function based Kriging model formulated as minimization of a negative log-likelihood function and (iii) length of the straight portion (L), angle of divergence (αd) and inlet swirl angle (αsw) of draft tube as explanatory variables. Flow in the draft tube is characterized by the presence of wall separation, recirculation and axial vortex rope occurring under different inlet swirl and angle of divergence. The study shows that a flow consisting of a low intensity axial vortex rope near the exit of the draft tube is desirable for better distribution of flow in the radial direction for preventing the wall separation and recirculation in high area ratio draft tubes. It is found that the design variable that controls the development and structure of axial vortex rope is the inlet swirl. Verification using CFD analysis showed that the process of optimization has been able to fine-tune the inlet swirl angle that facilitated an optimum sized vortex rope at the center to cause uniform exit axial velocity and improved flow diffusion without wall separation, resulting in significant improvement in Static Pressure Rise.

Bluff-body stabilized turbulent premixed flames represent a challenging canonical configuration for computational simulation and validation. Past simulation results from many research groups on the...

The response behavior of capillary tube attenuated pressure sensor arrangements is studied using a rotating detonation engine as a nonlinear pressure wave source. The resulting measured pressures a...

Understanding the physical mechanisms by which blast waves interact with their surroundings is paramount to protecting the safety of armed service personnel and equipment. This study evaluates and discusses modern technology used in blast pressure measurement as it relates to primary blast injuries such as traumatic brain injury. Factors influencing primary blast injury were established as peak overpressure, impulse, number, and frequency of shock impacts based on a literature review. A simulated confined-corridor breaching environment was used to establish the potential for variability in these key parameters depending on location in a confined blast environment. Wearable blast pressure monitors were compared experimentally to not only laboratory grade pressure transducers but also simulated and empirically modeled blast pressure and impulse predictions at scaled distances between 3.1 and $$13.6\,\hbox {m/kg}^{1/3}$$ from 100-g and 200-g suspended Composition C-4 detonations partially confined by the ground. surface ground reflection. Each measurement and predictive technique is detailed and comparatively summarized. Average deviation from the mean in collected pressure and impulse data ranged between 10 and 15%. The disparity in the measured data was lowest in the static pressure range where mild traumatic brain injury is reported to occur.

Along with the anti-cavitation performance, the high speed and the high power density, are the main trends in the development of centrifugal pumps. At present, the most effective method is to install an inducer in front of the impeller. However, the tip leakage of the inducer results in the vortex cavitation at the blade leading edge of the inducer, and the cavitating flow inside the inducer seriously interferes with the hydraulic behavior of the inducer as well as the impeller with the development of the cavitation, thus to badly affect the operational reliability of the high-speed centrifugal pump. In the present paper, the cavitating flow in a high-speed centrifugal pump with an inducer is investigated by numerical simulations and visual experiments for different cavitation numbers. A typical evolution process of the cavitation is shown, including the inception, the development and the deterioration. A general description of the pump head-drop phenomenon is made through the study of the local and global flow fields, and the relationship between the vapor distribution and the static pressure distribution along the inducer is determined to describe the evolution of the cavitation. This paper intends to provide the foundation for studying the overall cavitation state of a high-speed centrifugal pump, and designing the inducer with a better cavitation resistance.

We consider a three-dimensional unsteady flow with one, two, or four rotating detonation waves arising in an annular gap of an axially symmetric device between two parallel planes perpendicular to its symmetry axis. The corresponding problem is formulated and studied. It is assumed that there is a reservoir with quiescent homogeneous propane–air combustible mixture with given stagnation parameters; the mixture flows from the reservoir into the annular gap through its external cylindrical surface toward the symmetry axis, and the parameters of the mixture are determined by the pressure in the reservoir and the static pressure in the gap. The detonation products flow out from the gap into a space bounded on one side by an impermeable wall that is an extension of a side of the gap. Through a hole on the other side of the gap and through a conical output section with a half-opening angle of $$45^{\circ }$$ , the gas flows out from the engine into the external space. We formulate a model of detonation initiation by energy supply in which the direction of rotation of the detonation wave is defined by the position of the energy-release zone of the initiator with respect to the solid wall situated in a plane passing through the symmetry axis. After a while, this solid wall disappears (burns out). We obtain and analyze unsteady shock-wave structures that arise during the formation of a steady rotating detonation. We measure and compare thrust characteristics for different numbers of detonation waves. It was shown that the thrust weakly depends on the number of waves while the specific impulse increases with increasing number of waves. The study of rotating detonation at various values of the stagnation pressure was conducted. The calculation results show that at a stagnation pressure less than the critical value, the realization of rotating detonation is impossible. It is established that, depending on the stagnation pressure, qualitatively different shock-wave structures can be observed. The analysis is carried out within single-stage combustion kinetics by the numerical method based on the Godunov scheme with the use of an original software system developed for multi-parameter calculations and visualization of flows. The calculations were carried out on the Lomonosov supercomputer at Moscow State University.

In the centrifugal compressor applied in the automobile turbochargers, the asymmetric structure of volute causes the non-uniform flow field in the impeller and compressor stall. The non-uniformity of the flow field in the compressor can be reflected by the casing-wall static pressure distribution. In this study, by removing the volute and directly imposing different simplified static pressure boundary conditions at the diffuser outlet, the formation mechanism of casing-wall static pressure circumferential double-peak distribution of the compressor is explored. It is found that the mass flow rate is redistributed at the impeller outlet due to local high static pressure induced by the volute tongue, which results in the formation of two airflow regions with high velocity in the diffuser, ultimately leading to the static pressure circumferential double-peak distribution in the diffuser and the impeller. Noted that because of the existence of the blades, the airflow regions with high and low velocity formed in the diffuser are locked within a limited range of one or more widths of the blade passage. When the number of blades in the compressor is large, the static pressure can appear as multi-peak distribution in the circumferential direction. Moreover, the result of the mass flow rate redistribution at the impeller outlet is determined by the static pressure distribution characteristics at the diffuser outlet.

Detonation combustors are considered promising alternatives to conventional combustors because they offer high thermal efficiency and fast combustion. However, especially for the rotating detonation combustor, the theoretical propulsive performance has not been confirmed in experimental studies because the highly unsteady flow field hinders the measurements process. To understand the involved phenomena in more detail, a reflective shuttling detonation combustor (RSDC) with a rectangular combustion chamber was developed. The interior of the chamber can easily be visualized owing to its two-dimensional quality. Utilizing the RSDC, several combustion tests with gaseous ethylene and oxygen were conducted for different values of mass flow rates and equivalence ratios. Combustion modes from the tests were classified into four types based on the fast Fourier transform (FFT) analysis of the luminous intensity of the CH* self-luminescence images captured by a high-speed camera and a band pass filter. Simultaneously, the theoretical total pressure of a conventional isobaric combustor was compared to the static pressure measured at the bottom of the RSDC chamber. For the detonation modes, the ratio between experimentally measured static pressure and the theoretical pressure varied depending on the location in the chamber owing to the distribution of the time-averaged static pressure. Furthermore, the pressure ratio of the detonation modes was up to 18% lower than that of the deflagration mode potentially owing to the flow velocity induced by the detonation waves.

The paper presents an efficient method for analyzing complex periodic unsteady flows within turbomachinery. The method transforms the original initial value problem of unsteady flows to a boundary ...

Fluidization numbers varying from 0.84 to 1.68 were used in the loop seal valve of a bench-scale circulating fluidized bed (CFB) system to analyze the influence of the mono-chamber aeration mode on both the solids circulation rate and the static pressure drop inside the solids recycle device. Runs were carried out using 4 kg of overall solids inventory and particles of 183 µm in Sauter mean diameter, which were kept under fast fluidization regime at superficial gas velocity of 4 m/s. Results showed that the choice of the chamber to be aerated can noticeably affect the gas-solid hydrodynamics. In this sense, the analysis of variance applied on the experimental data indicated that the aeration into the recycle chamber of the loop seal offers lower levels of solids circulation rate but also allows to control it within a wider range of fluidization numbers and with less pressure drop or energy demand.

In a turbofan engine, the air is brought from the low to the high-pressure compressor through an intermediate compressor duct. Weight and design space limitations impel to its design as an S-shaped. Despite it, the intermediate duct has to guide the flow carefully to the high-pressure compressor without disturbances and flow separations hence, flow analysis within the duct has been attractive to the researchers ever since its inception. Consequently, a number of researchers and experimentalists from the aerospace industry could not keep themselves away from this research. Further demand for increasing by-pass ratio will change the shape and weight of the duct that uplift encourages them to continue research in this field. Innumerable studies related to S-shaped duct have proven that its performance depends on many factors like curvature, upstream compressor’s vortices, swirl, insertion of struts, geometrical aspects, Mach number and many more. The application of flow control devices, wall shape optimization techniques, and integrated concepts lead a better system performance and shorten the duct length. This review paper is an endeavor to encapsulate all the above aspects and finally, it can be concluded that the intermediate duct is a key component to keep the overall weight and specific fuel consumption low. The shape and curvature of the duct significantly affect the pressure distortion. The wall static pressure distribution along the inner wall significantly higher than that of the outer wall. Duct pressure loss enhances with the aggressive design of duct, incursion of struts, thick inlet boundary layer and higher swirl at the inlet. Thus, one should focus on research areas for better aerodynamic effects of the above parameters which give duct design with optimum pressure loss and non-uniformity within the duct.

In this study, a numerical analysis was conducted to investigate the effect of the tip clearance on the aerodynamic performance, internal flow characteristics, and stall region characteristics of an axial fan. Three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) calculations were conducted with a shear stress transport (SST) turbulence model. Tip clearance ratios of 0, 0.01, and 0.02 were applied to the impeller. As the tip clearance ratio increased, the aerodynamic performance of the axial fan decreased at both the design and the off-design conditions. The correlation between the tip leakage vortex (TLV) and the flow angle of the velocity triangle was presented for the difference in the tip clearance and flow rate. As the flow rate increased, the differences in the aerodynamic performance induced by the tip clearance ratio decreased. As the tip clearance ratio increased, the size of the TLV increased and gradually moved in the circumferential direction to interfere with the main flow at the low flow rate. Meanwhile, the size of the TLV was similar and gradually moved in the axial direction even if the tip clearance ratio increased at the high flow rate. The pressure fluctuations were observed by the fast Fourier transformation (FFT) analysis to compare and analyze internal flow characteristics at the stall region and design point. The static pressure was converted to the appropriate magnitude. The locations of the highest magnitude were shown to be different at the stall region and the design point, respectively.

This paper presents a reliability optimization design method for a hydraulic system that considers oil contamination. The proposed method applies the quantitative relationship between oil contamination and system reliability to the reliability design of a hydraulic system, while considering the performance, layout, and other design factors. A global reliability model of the hydraulic system is constructed based on the oil contamination control model. Further studies aiming at an optimization design model of the hydraulic system is established where the cost is the objective function, reliability index, size and structure range, performance requirements are constraints, structure size and oil change period are design variables. For illustration, a case study on the reliability optimization design of the oil supply point branch of the static pressure bracket of a certain type of heavy CNC horizontal lathe is considered.

Traditional chemical and mechanical descaling methods are expensive, inefficient and environmental pollution for removing scales in coal mine main drainage pipeline. In this study, a water jet is proposed to remove pipe scales, which can solve the inadequacies of traditional methods. Parametric optimization for water jet and descaling nozzle are analyzed. Firstly, the mechanical properties of scale materials are obtained for the first time by uniaxial compressive tests and Brazilian disk splitting tests. Secondly, crushing mechanism and crushing effect of pipe scale subjected to water jet are studied by AUTODYN software. Relationship between the nozzle’s key structure parameters and the axial static pressure and velocity of the fluid field inside the nozzle are analyzed by Fluent software. Moreover, the axial dynamic pressure and velocity of fluid field outside the nozzle are also analyzed. The above numerical simulations indicate that the pressure, flow and target distance of water jet should be 20 MPa, 40L/min and 50 mm, respectively; the outlet diameter, contraction angle and length-diameter ratio of the nozzle should be 2 mm, 13°and 2, respectively. Finally, experiments are conducted for the validation of these parameters. The results provide guidance for the development of the water jet descaling technique of the coal mine drainage pipeline.

The effect of Tandem-Hole configuration on penetration and combustion in supersonic crossflow was studied using three injectors having two tandem holes of 0.7 mm diameter with a spacing of 5, 10, a...

A research was carried out with the construction of a model of a low-pressure nozzle with aerodynamic fuel atomization, which shows the advantages of nozzles of this type. In order to reduce the time at the stage of development and calculations, modern computer design systems were used. The research was carried out in the Flow Simulation module of the SolidWorks software package, which allows you to calculate and build a model of the internal flow around the nozzle using already known parameters. These parameters were set through the program conditions panel: fuel consumption per second; air flow rate at the inlet to the nozzle; static pressure in the combustion chamber. The calculations performed by the module made it possible to evaluate the manufacturability of the design, as well as the internal processes of mixing fuel with air. To determine the quality of fine dispersion of the fuel atomization, a model of the velocity field was calculated over the entire section of the nozzle, from which it can be seen that the maximum flow rate of the fuel is achieved in the outlet channels of the fuel atomizer of the nozzle. The results obtained indicate the operation of the low-pressure principle while maintaining high-quality fuel atomization. The use of low-pressure nozzle with aerodynamic fuel atomization is possible in modern gas turbine engines of civil aircraft, as well as in gas turbine.

In this work, the behaviors of flow field and pressure fluctuations in both time and frequency domains in an axial flow pump through changing various impeller blade angles are studied and investigated by using a CFD technique. The blade angles are changed between 30°, 45o, 60o and 75o. Numerical results are validated with the experimental values, as a good agreement was found between them. The developed flow analysis shows that the blade angle does influence the different flow behaviors and features, such as the static pressure, turbulent kinetic energy (TKE), pressure fluctuations, axial velocity, radial velocity and tangential velocity. The results have revealed that the TKE rises with flow rate decreases and high static pressure increases at the pump outlet region near the tip blade region. Another conclusion of the study is the fact that the blade angle with 60o is the better one in terms of lower-negative-pressure regions, when compared with the other settings. The first dominated frequency was pump rotational frequency, and the second important frequency is the BPF (blade passing frequency). Furthermore, the results showed that impeller blade angles and unsteady flow have a high influence on the pressure fluctuation amplitude. Moreover, the results of the presented numerical simulation would be useful for a future hydraulic design of an axial pump.

Mechanical and metallurgical characteristics of the surface layers are modified as the material is subjected to the burnishing process. Plastic deformation is known as a major reason for property enhancement of the surface and subsurface layers. Residual stress distribution and influenced depth of plastic deformation provide useful information regarding the functionality and life cycles of the burnished sample. In the present study, a novel analytical approach was presented to predict residual stress distribution and the depth of plastic defamation in the ultrasonic-assisted ball burnishing process. The burnishing process was firstly analyzed using the contact mechanic of an elastic sphere with semi-infinite body theorem. Then, the plastic deformation and residual stress were modeled using the McDowell algorithm. The model could incorporate effects of vibration amplitude and frequency, static pressure, feed rate, and ball dimensions. A series of ultrasonic-assisted ball burnishing experiments have been carried out on aluminum 6061-T6 and AISI 1045 steel to confirm the proposed model prediction results. The prediction accuracy of the proposed model was further verified by residual stress distributions of AISI 304, Ti-6Al-4V, and Inconel 718 from other literatures. The research findings in this study indicated that the developed model could be used for a variety of engineering materials in the prediction of residual stress with adequate precision.

The compressor is one of the key components in the closed supercritical carbon dioxide (S-CO2) Brayton cycle, but its design method is far from mature. It is naturally expected that the well-established design method of the air compressor can provide favorable guidelines, on the basis of further understanding the effects of the physical property on the compressor flow field. Considering that isentropic compression is one of the core physical processes in the compressor, the physical property effects on this process were mainly investigated in this work. Similarity criterion was considered, and the change rate discrepancy of the main variables in this process between S-CO2 and the ideal air was fully analyzed. Results show that S-CO2 is compressed faster than the ideal air in most cases, along with generating smaller Mach number and larger pressure rise ratio. It is noted the important parameter of the static pressure coefficient distribution with S-CO2 in the compression process is almost the same as that with the ideal air at low Mach number, which is conductive to the extension of the air compressor research experience, but it is quite different at high Mach number. The simulation cases about compressor cascade are further applied and prove the suitability of the revealed physical property effects in the compressor passage. Understanding these effects on the compression process is helpful to improve the design method of the S-CO2 compressor.

This paper deals with a new development of a swash-plate hydraulic pump. It is particularly designed to aim its usage in applications where environmental impacts should be concerned. Thus, the pump is based on not mineral-based oil but simple tap water. The Electro-Hydraulic Actuator (EHA), a linear motion generator operated by an electric motor installed to the proposed pump, can be attractive and expandable to small-to-medium pressure applications. Water is clean and safe, and the size of EHA is relatively small. New design features of the pump including the no-shoe retainer, the inclination angle adjustment screw, the rotating cylinder block, and the simple assembly structure enabled EHA. The pump was designed to have its static pressure of 1.4 MPa and the volumetric flow rate of 10 × 103 mm3/s. To verify its performance, a series of experiments were constructed, and the maximum volumetric flow rate and pressure were found as 2935.87 mm3/s and 1.9 MPa, respectively. The maximum velocity of the actuator stroke was 9.35 mm/s. The EHA is controlled directly by the electric motor, and so a directional valve is not necessary. It is concluded the pump can be successfully used in small-to-medium pressure applications.

The transient response of a plate and a cavity is investigated in a supersonic wind tunnel start experiment where the freestream flow inside the test section reaches turbulent flow at Mach 2. Experimentally measured plate displacement time history shows flutter onset, transition to limit cycle oscillation, and stabilization at a static deformed state during the 30 s run. To analyze and interpret the measured plate response, a fully coupled aero-thermal-acousto-elastic analysis is carried out. A theoretical–computational model is formulated with a nonlinear structural plate model, acoustic pressure equation for the stationary fluid in a cavity, and the first-order Piston Theory aerodynamics. A linear stability analysis is performed that includes the nonlinear added stiffness due to an initial deformation to investigate the combined effects of freestream coupling and temperature differential on system stability. Also, direct time integration of the nonlinear fluid structural equations of motion is performed using experimentally measured flow parameters as inputs. All stability transitions are captured using the theoretical model with good agreement with experiment for transitions from no flutter to flutter/limit cycle oscillations (LCO) although the theoretical LCO amplitude is approximately $$50\%$$ larger than measured. The system’s sensitivity to cavity coupling, temperature differential, thickness calibration, static pressure differential, and turbulent pressure fluctuations are investigated. Lastly, snap-through buckling analyses in response to periodic and quasi-static excitations are conducted.

The effect of the change in the curvature of the stream and the execution attributes of straight walled and S-shaped rectangular diffusers having a center-length of 500 mm and an area ratio of 1.5 is studied in this paper. Straight and S-shaped diffusers with a square inlet and a rectangular outlet have been fabricated using an alternate turn angle. The cross-flow velocity, static pressure and total pressure variation along the length, at different sections of the diffusers, are measured using pressure tapings and normal three-hole probe. The low performance is due to the generation of secondary flows as a result of the geometrical curvature and the additional losses are due to the surface roughness of the diffusers. The total pressure loss coefficient for all the diffusers is nearly identical and seems to be independent of the angle of turn. In this paper, results were shown in the form of pressure recovery coefficient, coefficient of total pressure loss, average cross-flow velocity and flow deviation. Furthermore, pressure and velocity contours were developed for the entire study of all four designs of the diffuser.

Influence of different guide vanes on structural of flow field and axial pump performance under unsteady flow is carried out using numerical method. A three-dimensional axial flow pump model is numerically simulated using computational fluid dynamics (CFD) method with four number of impeller blades and 3, 4, 5 and 6 guide vanes depend on the SIMPLE code, standard turbulence k-ε model as well as sliding mesh method (SMM). The static, dynamic, total pressures, shear stress, velocity magnitude and turbulent kinetic energy are the important features which affecting instability operation in the pump. By monitoring above parameters and setting different measurement pressure points, the average pressures in the pump are discussed and the effect of guide vanes on the average pressure is analyzed. The results demonstrate that the numerical calculations can provide good accurately prediction for the characteristics of internal flow in the pump. The numerical results are closed to experimental results the minimum errors of pressure differences can reach 2.5% and the maximum errors 6.5%. The guide vanes have more effect on the flow field and pressure variations especially at outlet region in the axial pump. As compared with the using various guide vanes, the pressure increases as number of vanes increase that can lead the performance of pump also increases. Pressure differences in the pump at variety mass flow for vane 6 is higher than other vanes 3, 4 and 5 by 14.13, 11.35 and 3.85% for flow of 5 L/min. Further, the dynamic pressure differences for design flow between different vanes 6, 5, 4 and 3 are about by 2.87, 7.26 and 8.51% respectively.

The first objective of this work is the verification of a moving-body immersed boundary method for the direct computation of noise generated by rotor-stator interactions in transonic 2-D cascades. ...

The performance of compact, aggressive ducts in advanced propulsion systems is limited by the internal flow separation coupled with the formation of secondary counter-rotating vortices that give rise to intensive flow distortions at the duct exit. An experimental investigation was conducted to study the flow field and passive suppression of flow separation and Aerodynamic Interface Plane (AIP) distortion in a serpentine air inlet duct. Tests were performed by a turbofan engine at several Engine Operating Points (EOPs) from 56% (idle) to 100% (max). A large total pressure deficit region arose at the upper part of the AIP, which was associated with the upper surface flow separation. Using the new mechanical S-type vortex generators in two longitudinal positions (VG1 and VG2), separation and loss were diminished at the upper part of the duct and AIP. The VG2 arrangement attained the maximum reductions in distortion coefficients which were 73.72%, 60.7% and 37.8% in DC(90°), DC(60°) and ΔPC/P metrics, respectively. In the next step of the study, some unsteady aspects of the flow field were analyzed inside the duct. The separation onset and reattachment points were determined by the standard deviation of static pressure on the upper surface. The AIP spectral distribution showed that the boundary of low pressure and high pressure recovery regions was dominated by the maximum fluctuations. Furthermore, the PSD diagram of several probes at AIP revealed the vortex shedding frequency and its higher harmonics at separation region. The energy content of distinct unsteady spectral features in the bare configuration was significantly reduced using VGs, which showed the improvement of flow at the duct exit.

For some embedded engine arrangements, the nature of the inlet distortion is influenced by the boundary layer characteristics at the inlet plane of the intake. This research presents the first quantitative assessment on the influence of inlet boundary layer thickness and asymmetry on the swirl distortion at the exit of an S-shaped intake. Measurements of high spatial and temporal resolution have been acquired at the outlet plane of the S-duct using time-resolved particle image velocimetry. When boundary layer profiles typical of embedded engines are introduced, the characteristic secondary flows at the outlet plane are intensified. Overall, the peak swirl intensity increases by 40% for a boundary layer which is 7 times thicker than the reference case. The unsteady modes of the S-duct remain, although the dominant fluctuations in the flow arise at a frequency 50% lower. When the inlet boundary layer profile becomes asymmetric about the intake centerline the peak swirl events at the hub are reduced by up to 40%. At the tip the peak swirl intensity increases by 29%. The results demonstrate that the effects of inlet boundary layer thickness and asymmetry must be carefully considered as part of engine compatibility tests for complex intakes.

In order to improve chemical mechanical polishing (CMP) efficiency and accuracy in the fabrication of planar optics, CMP models and machine tools have been developed. A three-dimensional contour map of the surface of the polishing plate was established by measuring the runout error of several circles on the polishing plate. Based on the Preston equation and the three-dimensional contour map, a CMP model that simulates material removal at any point on the work piece is proposed. This model shows that higher motion accuracy can improve efficiency and accuracy. Then, based on this point of view, a new CMP machine tool was designed, and the ultra-precision gas static pressure guide rail and turntable and Siemens 840Dsl numerical control system were applied to the new CMP machine tool. In order to validate the new machine, a series of testing and processing experiments were carried out. The straightness error of the gas static pressure guide rail can be less than 1.1 μm. The axial runout error of the gas turntable can be less than ±0.4 μm. The surface profile of the experimental workpiece can be less than 0.01λ, and the processing efficiency of the new CMP machine can reach 4 times of the processing efficiency of the conventional CMP machine. In addition, the repeatability and stability of the CMP process is improved on new machines.

The drag coefficient of the nacelle lip-skin model was investigated to analyze the aerodynamic performance of the bias acoustic liner underneath the nacelle lip-skin at lowspeed free stream velocities. Drag coefficient reduction, using the bias flow of a bias acoustic liner on a nacelle lip-skin, is discussed for incompressible flow condition. The experimental data were recorded to analyze the nacelle lip-skin’s drag coefficients. The investigation covered four different bias flow areas to total nacelle lip-skin area ratios, ranging from 0 % to 12 %, at Reynolds numbers ranging from 2.2×105 to 3.5×105 and the nacelle internal static pressure of 0- 90 Pa, with the uncertainty of the experimental data being less than 10 %. The results show that the drag coefficient is reduced by up to 19 % as the ratio of the bias flow area to the total nacelle lip-skin area increases from 0 % to 12 %. In the transition flow regime, the drag coefficient increases gradually with Reynolds number. In addition, the optimum nacelle internal static pressure of present study was found to be 60 Pa.

The performance of an aircraft engine depends on air flow quality at the engine face / the exit of the air-intake also known as aerodynamic inlet plane (AIP). A single-engine aircraft has complex Y-shaped twin air-intake which causes severe flow separation, distortion and flow non-uniformity at the AIP. The present study compares the efficacy of slotted synthetic jet and a row of four circular synthetic jets attached to inner faces of a twin air-intake to improve aerodynamic performance at the AIP. The results are obtained using computational fluid dynamics. The velocity and vorticity plots show that lateral spread of the circular jets is limited as compared to the slotted jet. The circular jets are found to be weak as compared to slotted jet to prevent separation of main flow occurring in the twin air-intake. The various aerodynamic performance parameters, such as static pressure recovery coefficient, total pressure loss coefficient, distortion coefficient and secondary flow uniformity are compared for both the cases, exhibiting marked improvement in all these parameters. The study demonstrates that the slotted synthetic jets is a better option for controlling flow in twin air-intake as compared to a row of circular synthetic jets.

Research interest has been growing in recent years in supersonic transport, particularly supersonic propulsion systems. A key component of a commonly studied propulsion system, ramjets, is the air intake. For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery. This refers to the ratio of the average total pressure after the intake to that of the freestream. One phenomenon that can have a large effect on this performance index is flow separation at the inlet. The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet. This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel. Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ. Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance. Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone. Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake. At the optimal laser frequency, found for this Mach number to be 10 kHz, the pressure recovery is found to increase by up to 4.7%. When the laser power added to the system is considered, this results in an overall increase in propulsive power of 2.47%. Keywords: Laser energy deposition, Supersonic, Flow dynamics, Intakes, Flow separation

In this paper, the effect of different amount of protrusion on various parameters in rotor–stator system was experimentally studied by measuring CO2 concentration and pressure, in order to obtain the optimal protrusion amount. The parameters of different dimensionless sealing flow were measured under the condition that the annulus Reynolds number was 4.39 × 105 and the rotating Reynolds number was 1.05 × 106. The results show that the change of the amount of protrusions has little effect on the static pressure in the cavity, and the static pressure change near the sealing ring is almost negligible. But the total pressure and sealing efficiency increase first and then decrease with the increase of the amount of protrusion. The variation of power consumption is the same. A complex vortex structure will appear at the high radius region when the protrusion is installed. On the other hand, the protrusion can effectively reduce the minimum sealing flow of the rotor–stator cavity. Furthermore, considering the sealing efficiency and power consumption, the best range of the protrusion amount is about 36. The ratio near this range can optimally balance the alleviation of the gas ingestion and the reduction of the power consumption. Keywords: Gas ingestion, Protrusion amount, Radial seal, Rotor–stator cavity, Sealing efficiency, Turbine