Investigation Of Flow Separation Control And Optimization Of Vortex Generator Jets For Axial Flow Compressor

The flow separation phenomenon in the cascade passage is more and more serious with the increasing of compressor load,which suppresses the improvement of the compressor performance.In addition to adopting three-dimensional blade design technology to organize flow,flow control technology is also an important means to control the corner separation.Vortex generator jets,an active flow control method,integrate the control characteristics of the passive vortex generator and active blowing,which greatly expands its potential in the flow control application of the compressor.In the dissertation,the high subsonic compressor cascade NACA-65K48 and the transonic compressor NASA-Stage37 are taken as the research objects.The experimental and numerical optimization studies of the end-wall vortex generator jets on the corner separation control of the axial compressor are systematically carried out.As the basis of optimization research,first,the optimization algorithm program based on the Kriging model is completed.The hierarchical Kriging model,gradient enhanced Kriging model,single-point infill sampling criteria,and parallel infill sampling criteria are written.The single-objective,multi-objective,and robust optimization process based on the Kriging model are given.The pseudo-EI criterion is introduced into the minimizing the predicted objective function criteria and probability of improvement criteria.An adaptive distance infill sampling criteria are developed.The test function and inverse design of airfoil are used for comparison and verification.The results show that the MP criterion using the adaptive distance has higher efficiency and is not easy to fall into a local optimum.The parallel optimization algorithm including the EI criterion has stronger global searchability.The flow separation control on the high-subsonic compressor cascade using end wall vortex generator jets is studied with the experimental methods.The inlet Mach number is 0.7.The effects of jet mass flow and incidence angle are mainly discussed.The aerodynamic parameters at the outlet and the static pressure on the wall are measured.The oil flow methods are used to calibrate the separation flow on the wall.The results show that the end wall vortex generator jets can effectively reduce the secondary flow loss in the corner of the cascade.As the jet mass flow increases,the control effect is gradually improved.The main loss reduction is the secondary flow loss.The mixing loss near the end wall gradually increases,and the width of the wake increases.The control effect under the variable incident angle is weakened.It is mainly due to the increase of mixing loss near the end wall under the negative incident angle,the boundary layer separation of the suction surface is enhanced under the positive incident angle,and the end wall jet has a weak effect on the boundary layer separation.The numerical method is used to carry out the optimization study of the end-wall vortex generator jets combined with the optimization algorithm.The optimal jet parameters are obtained.The parameter control law is summarized.Robust optimization analysis of the jet parameters based on the surrogate model is performed.The main topology and vortex structure of the cascade flow field is given before and after the control.The results show that the optimal result can minimize the separation of the suction surface and block the cross flow into the corner,but it cannot eliminate the low momentum fluid.So the loss near the end wall area is still obvious.The optimization study of the jet hole exit shape is carried out based on the surrogate model.The control points are represented with a binary coded and initialized with the B-spline.The results show that this method can improve the control effect with a small jet mass flow.Under the condition of controlling the area of the exit hole,the ‘three-petal flower’ pattern can organize the jet flow to enhance the control effect.A numerical study on the optimization of the parameters of the double hole jet is carried out,and the distribution law of the optimal parameters of the double hole is summarized to provide a reference for the porous scheme.Finally,it is shown that the circumferential arrangement and streamwise arrangement have the best control effect.The pulsed end-wall jets are further studied with the numerical simulation.The excitation form,excitation frequency,duty cycle,and excitation mass flow are mainly studied.Proper Orthogonal Decomposition method is used to analyze the fluctuating flow field before and after the control.The results show that the pulsed end-wall vortex generator jet still suppresses the secondary flow by the continuous jet vortex,and the influence of the excitation form on the control effect is weak.The high duty cycle can enhance the time of jet blocking.The low-frequency case can provide time for the development of the jet vortex due to the long rising edge time.POD decomposition shows that the flow field of the baseline cascade has high steadiness and regularity.The low-frequency excitation case suppresses highfrequency pulsations in the flow field.The main mode in the flow field is the lowfrequency large vortex structures.The high-frequency case couple and strengthen the high-frequency pulsations.Finally,the end wall vortex generator jet is introduced into the transonic compressor stage,and its application prospect in a real compressor is discussed.The adiabatic efficiency and pressure ratio are used as the optimization goals at the highest efficiency point.The optimal jet parameter solution set is obtained.The control effect of the characteristic scheme under the expansion of stability margin and non-design speed is studied.The results show that the optimal cases are mainly distributed before the leading edge and near the suction surface separation.The parameter change law is close to that of the cascade.The optimization result of the highest efficiency point can improve the stability margin at the design speed,but the control effect of the non-design speed is not ideal.Because the stall mode of the stationary blade at the non-design speed has changed,the jet parameters at the design speed cannot be directly applied.