Study On The Corner Separation And Loss In Compressor

Nowadays,in order to develop the aerodynamic performance of the compressor,especially the high pressure ratio,it is needed to increase the stage pressure ratio,which will create more complex secondary flow in the compressor,particularly in the regions near the blade tip and hub corner.And according to the recent researches,the corner separation phenomenon near the hub will cause a large scale of loss and even make the compressor come into stall situation,which is more serious.Thus,in this paper,the development of the corner separation and the loss distribution will be investigated with the help of CFD method.Meanwhile,combining with the hotspot about the blade surface roughness,the effect of blade surface roughness on the corner separation and loss distribution to the cascade was studied.Apart from this,with the help of the numerical optimization means,the aerodynamic performance of a low-speed fan was studied by optimizing the installation angle of different sections.Brief introduction is listed below.(1)the corner separation in the hub was studied by means of the CFD,which was based on a low-speed and high-load axial flow compressor cascade.Based on the topological analysis of the streamline on the wall,the distribution of the singular points and the corresponding separation line as well as attachment line were studied.And this paper also investigated the development of all kinds of vortex in the cascade.Based on the three-dimensional streamlines,the threesource theory about how passage vortex generated was put forward,and the corresponding model of the cascade vortex structure was established.Through the above analysis,the position extraction method of channel vortex is established,and the development characteristics of channel vortex were explored.At the same time,the losses in the cascade under the diagonal separation of the dissipative function were investigated.(2)Low-Reynolds compressor cascade was studied to investigate that whether the roughness on the blade can promote the 3D separation and make a difference on all type of the loss in the cascade or not by CFX.In this study,the Gamma transition model was introduced to investigate the influence of blade surface roughness to transition phenomenon.It can be concluded that the blade surface roughness has more effect on the separation transition and the bypass transition than the reverse transition.Furthermore,a detailed loss sources analysis model was used to study the loss influenced by the surface roughness,which divided the total loss in the cascade into the leading edge loss,the surface friction loss,the secondary flow loss and the wake flow loss.The results show that the total loss increases to 9.6% at large scale of corner separation condition when the equivalent sand grain roughness in the blades increases to 50μm.And the leading edge loss is most sensitive to the surface roughness.With the help of the topology analysis method,it can be found that the movement of the separation bubble is the most obvious phenomenon in the field as the roughness increasing.(3)According to the numerical results,it’s found that there are three kinds of typical secondary flow in a low-speed fan,the vortex structure induced by the spiral points at the hub and casing on the suction surface and the separation around the pressure side on the blade.With the increase of the flow rate,the separation in the pressure blade increases sharply until the entire blade height is covered,which leads to an increase in entropy.Moreover,neural network optimization algorithm was used to improve the aerodynamic performance of the fan,which divided the stator blade into eight sections along the span direction,and treats the stagger anger of each section as the optimization variable and static pressure efficiency as the optimization objective.At the same time,the flow field of the optimal result was compared with the base stator,and it was found that the pressure surface separation was inhibited.