On The Design Method And Inner Flow Of High Speed Multi-stage Low Reaction Aspirated Compressor

The low reaction aspiration-in-stator compressor design philosophy provides a new way for the aerodynamic design of the highly-loaded compressor,and at the given tip speed,it could increase the compressor loading coefficient significantly.In view of a compressor of an aeroengine with the thrust-weight ratio of 15 and higher,the present research is aimed to give a deep discussion on the design method of the low reaction aspirated compressor and its inner complex flow mechanism by means of numerical method and theoretical analysis.Specific studies are as follows.Though the one-dimension aerodynamic design of a single highly-loaded compressor,the influences of reaction and axial velocity ratio on the key aerodynamic parameters of the rotor and stator are discussed in detail,with the aim to clarify the differences between the two different low reaction design philosophy.Furthermore,the increasing axial velocity method is introduced into the non-aspiration stages,achieving the transition of design contradiction among the stages.Based on this,a three-stage aspirated compressor is designed out using the low reaction design philosophy.Detail explanations on the selection of key design parameters and design method of the aspirated stators are provided.In the meantime,performance evaluation is also carried out on the multi-stage low reaction compressor at variant rotation speed.The numerical result shows that,the three-stage low reaction compressor achieves the design goal.At the tip speed of 356 m/s,the total pressure ratio attains 6 at the design operating point with the throughflow efficiency higher than 87%.The loading coefficients of the first and the last aspirated stages are 0.782 and 0.55 separately,and the loading coefficient of the middle non-aspiration stage also achieves 0.54.According to the flow analysis,the multi-stage low reaction compressor designed in this paper has good aerodynamic performance at variant rotation speed,and at lower rotation speed,the throughflow performance gets improved due to the decreased inlet Mach number.Close to the stall condition,the stall can be postponed via increasing the upper endwall slot suction flow rate of the first stage aspirated stator.The effect of tip clearance size on the performance of the first stage low reaction transonic rotor is performed to explore whether it is necessary to conduct tip clearance seal on it.Both flow structures and blockage in the rotor are analyzed at variant tip clearance.The stall mechanism at zero tip clearance is also elaborated by means of the unsteady numerical method.Though the axial momentum coefficient,dispassion function and different vortex detection methods,the development of the tip leakage vortex at variant tip clearance is presented.The numerical results show that,the stall mechanism is not same at different tip clearance.Compared with the zero tip clearance,the tip leakage flow can broaden the rotor working range,while at larger tip clearance,the tip leakage vortex is broken down partially,leading to a performance degradation and narrow working range.To control the tip leakage flow at larger tip clearance,the bowed blade is applied into the rotor.As a result,the negative bowed blade can be used to weaken the tip leakage flow and lower the sensitivity of the performance and working range to the tip clearance.While the positive bowed blade presents a converse effect.With regard to the outlet vane,the blade is fairly thin.Limited by the mechanical constraints,it seems impractical to implement the boundary layer suction on the blade suction surface.To address this issue,a compound flow control method,composed of tandem cascade and endwall boundary layer suction,is proposed.The design philosophy is to use tandem cascade to control the boundary layer separation and to utilize EBLS to suppress the corner stall.The basic implement strategy of the compound flow control method is presented.The influence of loading split on the stator loss characteristics is discussed,and meanwhile,its effectiveness is also verified at variant working condition.The result show that,with lower suction flow rate,the stator designed based on the compound flow control method achieves a diffusion factor of 0.665 at 0° incidence,and also has a considerable incidence range.As the tandem cascade is constructed reasonably,the endwall suction is merely required in the forward blade suction side corner.To further enhance the flow control ability of the compound flow control method,the non-axisymmetric endwall contouring is integrated into the stator.The endwall is parameterized via the nonuniform rational B-spline surface,and a multi-points optimization strategy is selected to minimize the aerodynamic loss generated in the stator.The optimized result shows that,the corner separation in the rear blade is well controlled with the supplement of endwall contouring at lower loading condition,while at higher positive incidence,flow in the forward blade corner is deteriorated.By analyzing the distribution of the suction flow rate,the endwall suction flow path is redesigned,which weakens the negative influence of endwall contouring on the stator performance at higher positive incidence effectively.Finally,the compound flow control method is applied into the outlet vane preliminarily,and its effectiveness is verified in the stage environment.To explorer whether the aspirated compressor designed based on the steady assumption could still meet the design demands under unsteady condition,threedimensional unsteady simulations are conducted on the first supersonic stage at near design and a lower flow rate operating points,with the inclusion of the suction side aspiration flow path.Emphasize are paid on the interaction between the stator extended shock and the rotor.Meanwhile,the influences of rotor wake on the development of stator boundary layer and the distribution of the suction flow rate are also analyzed.The results show that,though the aerodynamic performance is decreased slightly,the first supersonic stage still presents a higher throughflow efficiency under unsteady condition and the fluctuation of the outlet parameters is very small.At last,the explanation for the performance degradation under unsteady condition is uncovered.What's more,the direction of further improvement for the aspirated compressor is also proposed from viewpoint of the unsteady condition.