Dynamic Stall Inception And Multi-Scale Unsteady Aerodynamic Stability Investigation Of Fan/Compressor

Active control is one of the most important methods to increase usable stall margin of fan/compressor, the key point of which is stall inception including kind of stall-before disturbance, first position where stall-before disturbance and stall cell come out, and process of stall-before disturbance turning into stall cell. In the past few decades, great progresses in stall inception have been made by many researchers. Unfortunately, there are still no affirmatory conlusions about causations of stall-before disturbance and stall cell, process of stall-before disturbance turning into stall cell, and effect of distortion on stall inception.For the purposes of strengthen the understanding of stall inception, expose the effect of distortion on stall inception, and provide experimental data used to compare with numerical results. By installing high natural frequency pressure transducers in circumferential, radial and axial directions, this dissertation investigates the stall inception of a two-stage low speed axial flow compressor. Fisrt, stall inception with uniform inlet flow is researched. Characteristic of stall-before disturbance, causation of stall cell, and evolution of disturbance and stall cell are analyzed. Second, the effects of radial total pressure distortion, circumferential total pressure distortion and rotating total pressure distortion are analyzed respectively. The experimental results show that: (1) Modal wave type stall inception is three-dimensional and unsteady. Both of modal wave and stall cell come out in local position. (2) Radial total pressure would change the three-dimensional and unsteady characteristics of stall inception by altering radial distribution of variables. (3) Circumferential total pressure would change three-dimensional and unsteady characteristics of stall inception by altering circumferential distribution of variables. (4) The effect of rotating distortion on stall inception depends on rotating speed of distortion. (5) The causation of stall cell is related to suction surface boundary layer separation.Numerical simulation is an important means to analyze stall inception. Configurations of spike type disturbance and stall cell are three-dimentional and both of them rotate at part speed of rotor, therefor, numerical simulation method should have the ability to describe three-dimensional and unsteady flow field. In order to analyze stall inception of fan/compressore with suitable numerical method, a three-dimensional compressible unsteady model based on three-dimensional unsteady actuator disk model and compressible Euler equations is developed. By using this computation code, stall inception of a low speed axial flow compressor is investigated. The computional results are coincidence with the experiment results. Computation of stall inception of a high pressure five-stage Compressore and a three-stage transonic fan are also completed, the results show that this code could simulation spike type stall inception and has the ability to simulate both of rotating stall and surge. Radial distribution of axisymmetric total-static pressure ratio will affect the occurance position of stall cell.There are many different scales of unsteady flows in fan/compressor. Aerodynamic unstable flows including rotating stall and surge are the especial unsteady flow phenomenon, occurance and performance of which are related to other unsteady flows. Whether inlet flow is uniform or distortion, aerodynamic stability is a muti-scale and unsteady problem which refers to many scales unsteady flow in fan/compressor. Unless researching aerodynamic stability with muti-scale unsteady viewpoint, prediction stability boundary will not be corrected, required stall margin will not be reduced, and usable stall margin will not be increased.In order to research the multi-scale unsteady aerodynamic stability of fan/compressor, a two-stage low speed axial flow compressor with large scale unsteady outer disturbance has been investigated. The results show that multi-scale unsteady aerodynamic stability is really existed in fan/compressor. Large scale unsteady outer disturbance will affect the performance of suction surface boundary separation flow, and at the same time fan/compressor will impact on the performace of outer disturbance. Effect of outer disturbance on aerodynamic stability is associated with the relative speed of outer disturbance and rotor.