Boundary layer separation control on a highly-loaded, low-solidity compressor cascade

Separated flow can be effectively controlled through the management of blade boundary layer development. Numerical simulations on a highly-loaded, low-solidity compressor cascade indicate that combined blowing and suction flow control technique can significantly improve cascade performance, especially in increasing the cascade loading and static pressure ratio as well as decreasing the loss coefficient. Meanwhile, it is more effective to improve cascade performance by blowing near leading edge on suction surface than suction near trailing edge. Both the locations and flow rates of blowing and suction are major impact factors of this method to cascade performance. Comparing to the baseline, the static pressure ratio increases by 15% and loss coefficient decreases by 80%, with a blowing fraction of 1.7% and a suction fraction of 1.38% of the inlet mass flow.     

Flow control effect on unsteadiness of shock wave induced separation

In usual cases of significant pressure gradients and strong shocks, the front shock takes a fixed location along the wall, at which separation starts. Usually the rear shock is responding to vortex sheding by its deflection angle. In consequence main shock and rear shocks are moving whilst front shock is stable. The goal of the measurements presented here is to find out how the k-foot behaves during shock oscillations in the case when front shock is not fixed by the pressure gradient. Unsteady shock behaviour is also investigated when air jet vortex generators （AJVG） are used. Counteraction of the separation is directly related to the influence on unsteady processes in the shock wave induced separation.     

Numerical study on the suppression of shock induced separation on the non-adiabatic wall

IntroductionThe supersonic flow inevitably encounters the shockwaves that are in contact with the solid walls on which theturbulent boundary layer is developed. This sitUationproduces locally a complex phenomenon known as shockwave/turbulent boundary layer interaction. Basic stlldiesof the complex combinations of heat transfer andcompressibility are required to understand their effects onthe turbulent boundary layer characteristics. If the shockwave is strong enough, then the boundary layer c…     

Unsteadiness of Shock Wave／Boundary Layer Interaction in Supersonic Cascade

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Effect of nonequilibrium condensation of moist air on transonic flow fields

luttoductionMany studies on condensation occwhng in the caseof the rapid expansion of moist air mr steam in asupersonic nozzle have been performed experimentallyand numerically, and the characteristics of condensationhave been nearly clchfiedll4]. Schnerr et al.[5] and lriya atal.le] investigated the effect of condensation on thestrength of shock wave on suiface of wing, drag and liftnumerically. However, the. effect of condensation on theshock wave on s~e of wing and talulences behindshock wa…     

Influences of a kind of groove-blade on the flow field in a compressor cascade

This paper presents an experimental investigation of effects of a kind of streamwise-grooved blades on the flowfield in a compressor cascade.The flow field downstream the cascade and the boundary layer on the suctionsurface were measured using a mini 5-hole pressure probe at different incidence angles.The flow field in thegroove cascade was compared with that in the smooth cascade.The measurement results indicate that:(1)thegroove surface can restrain the development of the boundary layer on the suction surface;(2)the grooves canrestrain the radial migration of the low-energy fluids in the boundary layer on the suction surface;(3)the grooveblades can reduce total pressure loss and flow blockage in the cascade at the incidence angles of 0°,5°and 8°;(4)the maximum benefit of 8.6% loss reduction was obtained at the incidence angle of 5° while negative benefit of-3.0% loss reduction occurred at the incidence angle of-5°.     

Numerical investigation of tip clearance effects in an axial transonic compressor

Numerical investigations of the Darmstadt transonic single stage compressor (DTC), in the Rotor1-Stator1 configuration, aimed at advancing the understanding of the effect of different rotor tip gaps and transition modelling on the blade surfaces are presented. Steady three dimensional Reynolds Averaged Navier Stokes (RANS) simulations were performed to obtain the flow fields for the different configurations at different operating conditions using the RANS-Solver TRACE. The stage geometry and the multi-block structured grid were generated by G3DMESH and a grid sensitivity analysis was conducted. For the clearance gap region, a fully gridded special H-grid was chosen. Comparisons were made between the flow characteristic at design speed, representative for a transonic flow regime, and at 65% speed, representative for a subsonic flow regime. The computations were used to analyse the flow phenomena through the tip clearance region for the different configurations and their impact on the performance of the compressor stage.     

带真空腔周向槽抽吸影响跨声速压气机转子气动性能的数值研究

为探究附面层抽吸对跨声速压气机气动性能的影响,本研究利用数值方法对跨声速压气机转子进行模拟研究。在低抽吸流量下,对比单抽吸槽及双抽吸槽对跨声速压气机转子内部流动的改善效果,观察原型及转子压气机内部的流动状态,发现:抽吸流量为主流1%时,机匣周向槽抽吸处理可以改善转子上端流道流动状态,最大可使效率提高1.21%,压比提高2.53%,单抽吸槽抽吸效果更佳。     

Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

<正>It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall inception.Steady and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same rotor.For steady analysis,the predicted results agree well with the experimental data for the estimation of compressor rotor global performance.For unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade passage.On the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale-spike type rotating stall inception at blade tip region.It was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased,the rotating stall cell was further developed in the blade passage.     

Passive Control of Transonic Flow Fields with Shock Wave Using Non—equilibrium Condensation and Porous wall

When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.     

The effect of air humidity on shock wave induced incipient separation

InttoductionTtansonic flows often aPPear in modem tecbocalaPPlications. The most boleal examples are in civil andmilitary aeroplanes, but it also concerns the advancingblades of a helicopter rotor, supersonic jab engine intakesas well as compressor and tUlbine cascades.The crucial phenomenon Which is inVolved in suchnows is the formation of shock waves and theirinteraction with bounce layers adjacent to boundingwalls. Shock waves Which introduce the rapid increase ofparameters impose an ad…     

Experimental research of surface roughness effects on highly-loaded compressor cascade aerodynamics

Aircraft engines deteriorate during continuous operation under the action of external factors including fouling, corrosion, and abrasion. The increased surface roughness of compressor passage walls limits airflow and leads to flow loss. However, the partial increase of roughness may also restrain flow separation and reduce flow loss. It is necessary to explore methods that will lower compressor deterioration, thereby improving the overall performance. The experimental research on the effects of surface roughness on highly loaded compressor cascade aerodynamics has been conducted in a low-speed linear cascade wind tunnel. The different levels of roughness are arranged on the suction surface and pressure surface, respectively. Ink-trace flow visualization has been used to measure the flow field on the walls of cascades, and a five-hole probe has been traversed across one pitch at the outlet. By comparing the total pressure loss coefficient, the distributions of the secondary-flow speed vector, and flow fields of various cases, the effects of surface roughness on the aerodynamics of a highly loaded compressor cascade are analyzed and discussed. The results show that adding surface roughness on the suction surface and pressure surface make the loss decrease in most cases. Increasing the surface roughness on the suction surface causes reduced flow speed near the blade, which helps to decrease mixing loss at the cascades outlet. Meanwhile, adding surface roughness on the suction surface restrains flow separation, leading to less flow loss. Various levels of surface roughness mostly weaken the flow turning capacity to various degrees, except in specific cases.     

Unsteady transonic flow control around an airfoil in a channel

Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle fatigue failure and so on. Present study investigates the effectiveness of perforated cavity to control this unsteady flow field. The cavity has been incorporated on the airfoil surface. The degree of perforation of the cavity is kept constant as 30%. However, the number of openings (perforation) at the cavity upper wall has been varied. Results showed that this passive control reduces the strength of shock wave compared to that of baseline airfoil. As a result, the intensity of shock wave/boundary layer interaction and the root mean square (RMS) of pressure oscillation around the airfoil have been reduced with the control method.     

Numerical investigation on effectiveness of flow separation control in two-dimensional high-load compressor cascade by synthetic jet

The effectiveness of flow separation control in two-dimensional high load cascade by synthetic jet is investigated through numerical simulation of the effect of excitation frequency and amplitude together with the adaptability of synthetic jet to off-design conditions. Test results indicate that synthetic jet can be used to effectively control the large-scale two-dimensional flow separation in compressor cascade. Preferable results can be obtained when excitation frequency is close to or times of the characteristic frequency of original flow field. Excitation amplitude has a more important effect on the effectiveness of flow separation control, and the increase in excitation amplitude can bring about a dramatic decrease in the loss of total pressure. Synthetic jet has also a very good adaptability to off-design conditions. It can therefore be concluded that the incidence sensitivity of compressor cascade can be effectively reduced by synthetic jet.     

An improvement on the efficiency of a single rotor transonic compressor by reducing the shock wave strength on the blade suction surfaces

It is well known that increasing the rotational velocity is an effective way to increase the total pressure ratio. With increasing flow velocity especially under the condition of transonic flow in the supersonic region, where exist strong shock waves, the shock wave loss becomes main and important. Simultaneously, there occurs boundary layer separation due to the shock wave / boundary layer interaction. In the present paper the transonic compressor blades were studied and analyzed to find a proper and simple way to reduce the shock wave loss by optimizing the suction surface configuration or controlling the gradient of isentropic Mach number on the suction surface. A Navier-Stokes solver combined with a modified design algorithm was developed and used. The NASA single rotor for transonic flow compressor was served as a numerical example to show the effectiveness of this method. Two cases for both original and modified rotors were analyzed and compared.     

Numerical Study of Interaction of Propagated Shock with Boundary Layer Behind Contact Surface in Ducts

The interactions of the shock with the boundary layer of the cold gas behind the contact in many different conditions, i.e. three kinds of test gases and three kinds of sound speed ratios across the contact, were explored by numerical study. The trajectories of the transmitted shock in cold gas flow and the development of shock bifurcation in the process of interaction with boundary layer are illustrated by many kinds of figures (e.g. the time-distance diagrams of the acoustic impedance contours on the axis, the pressure and density contours and the static pressure distributions on the axis).     

Numerical investigation of aerodynamic performance influenced by circumferentially pre-swirling coming flow on the crossover and de-swirling cascade of a multistage centrifugal compressor

Numerical investigation is implemented on aerodynamic performance inside the crossover and de-swirling cascade of a multistage centrifugal compressor. The emphasis is put on the aerodynamic performance influenced by the circumferentially pre-swirling coming flow. The results indicate that flow separation occurs inside the crossover, and the separation area may be changed with different circumferentially pre-swirling coming flow. Decreased pre-swirling intensity of the coming flow may effectively restrain the flow separation and make the outflow from the crossover more uniform, which helps to improve the aerodynamic performance of the successive de-swirling cascade. The flow inside the de-swirling cascade is a non-uniform swirling flow with large separation. The complex secondary flow occurs along the main flow and experiences a process of generating, developing, dissipating and collapsing. __________ Translated from Power Engineering, 2007, 27(1): 24–28, 49 [译自: 动力工程]     

Numerical study of shock waves propagating through right angled multiple elbows

Introduction The elbow is one of the important elements used in pipe lines, and it is very important to clarify the propagating phenomena of shock waves through the elbow for engineering applications. Although some investigations of the propagating shock in the single and double elbows have been carried out[1?The working gas is air. The numbers of the grid in the computational domain are 251·(a) Type 4-1 (b) Type 4-2 Fig.3 Pressure distributions on each wall the merging with the 2nd shock…     

Experimental Investigation of the Three—Dimensional Flow in an Annular Compressor Cascade at Large Incidence

This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence)on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence anglesunder low Mach number and low Reynolds number conditions.Experimental techniquss include the oil-filmvisualization on the profile and the endwall surfaces,the laser-sheet visualization of the flow field inside theblade passage,and the measurement by radial-circumferential traveress using a seven-hole probe.The behaviorand nature of the three-dimensional flow with severe separations inside the blade passage and at the exit areobtained.The distributions of the total pressure loss,static pressure,velocity and outflow angle are also given.These results are valuable for establishing the physical model of the three-dimensional complex flow in axialcompressors and for examining the computational procedures.     

Numerical analysis of shock induced separation delay by air humidity

In this paper numerical calculations of the dry and humid air flows in the nozzle are presented. The dry air flow (adiabatic flow) and the humid air flow (flow with homogeneous condensation, diabatic flow) are modeled with the use of Reynolds Averaged Navier-Stokes (RANS) equations. The comparison of these two types of flow is carried out. The influence of the air humidity on the shock wave location and its interaction with the boundary layer is examined. Obtained numerical results present a first numerical approach of the condensation and evaporation process in transonic flow of humid air. The phenomena considered here are very complex and complicated and need further in-depth numerical analysis.