Research On The Characteristic Of Separated Flow In Compressor And Its Control Strategy

The performance improvement of the compressor has a significant impact on further improving the power-to-weight ratio of advanced aviation power.Due to the large inverse pressure gradient in the compressor,it is easy to occur the flow separation phenomenon at the suction surface and the corner area,which limits the further improvement of the compressor performance.Based on the study of the characteristics of the separation flow in the suction surface and the corner area,the employment of unsteady flow control technology can improve the performance of the compressor and thus the overall level of the aeroengine can be improved.Numerical simulation and experiments were introduced to study the characteristics of these two types of separation flow in compressors and corresponding unsteady control strategies.The main work is as follows:Starting from N-S function,a kind of global stability analysis methods suitable for multidimensional separated flows was developed.This method overcomes the difficulties that the classical stability analysis method(O-S function)can only be applied to the limitation of one-dimensional flow,and also solves the problem when using conformal transformation method would meet,such as poor calculation efficiency and less applicable flow.A verification study of the two-dimensional pressure cap drive flow was carried out.The results obtained in this paper are consistent with the published results,which verifies the accuracy of the method introduced in this paper.Based on this,the effect of GPU on its acceleration performance in the solution process was further studied.Aiming at the specific flow problem of separation on the suction surface of compressor,a global stability analysis method for this kind of flow was established.The results show that this method can capture the global instability characteristics of suction separation flow.The most unstable frequency is close to the main frequency of the separation vortex in the flow field.This method can also be used to guide the selection of dynamic excitation parameters for fan / compressor suction separation control.It provides a theoretical basis for the frequency selection of unsteady flow control parameters.Based on this,an unsteady pulsed suction flow control method was proposed,and the control law of the pulsed suction control parameters on the separation flow was obtained.The self-synchronization and threshold effects of unsteady flow control were investigated and illustrated by the method of bi-global stability method.Based on the topological structure of the corner separation stall and the surface vortex instability,a simplified model for refining the corner stall into two orthogonal transverse vortex layers was proposed and the corresponding research method was illustrated.The influence of the degree of expansion on the total pressure loss were investigated.The dynamic evolution of two orthogonal transverse vortex layers and the turbulent anisotropy in the corner separation stall state were obtained.The theory of DMD method was further analyzed,and the rationality of using real part of DMD mode to show its spatial structure was illustrated.A function,which can be used to express the contribution of the imaginary part and conjugate modes to the evolution of the DMD modes over time,was obtained.Then,the dynamic mode decomposition method was introduced to further study the charecteristics of corner stall and the corresponding dynamic characteristics under were studied.The mechanism of the symmetry breaking phenomenon was preliminarily explained,and corresponding experimental research was carried out to verify the accuracy of the numerical simulation.Combining micropulse technology and the dynamic evolution characteristics of the two lateral vortex layers,two kinds of phase-controlled unsteady method were proposed to suppress the corner stall,which have the advantages of simple and reliable structure,and easy engineering implementation.An experimental study was carried out on one of this kind of structural forms,and the influence law of the unsteady excitation phase on the control effect of separated flow was obtained.The validity and feasibility of the scheme were initially verified.Combining the turbulence characteristics and unsteady control law of the flow field,the mechanism of bilateral unsteady excitation to suppress corner separation stall was discussed.