Research On Leakage Characteristics Of Hub Cavity Flows In Planar Diffuser Cascade

In this paper,the numerical calculation of the plane diffuser cascade with the stator cavity and the three-stage labyrinth seal is carried out,the topological analysis of the gapless cascade surface is carried out,the three-dimensional streamlines distribution of the cascade corner region is studied respectively for the presence or absence of leakage,the total pressure loss of each channel surface in flow direction,the blade load of different blade heights and the flow parameters of the inlet and outlet sections were compared,and the mechanism between leakage flow and mainstream was analyzed.The leakage flow structure and the aerodynamic parameters of each section are discussed with the variety of inlet Mach number,angle of attack and the speed of hub,on this basis,the upstream cavity configuration is optimized,and the new configuration of the cavity outlet rounding and the two sidewall ribs of the cavity is designed,which got some optimal effects.The main conclusions of this paper are as follows:1.The total pressure loss of gas flowing through the cascade channel without leakage is mainly from the corner zone of the blade root,the flow separation mainly starts at the proximal wall boundary layer,with the transverse pressure gradient,the low-energy fluid on the pressure surface side is continuously accumulated on the suction side,which causes the deflection of the main flow,the flow from the pressure side to the suction side at the trailing edge of the blade further increases the complexity of the flow in the corner zone.The secondary flow structure of the cascade channel changes obviously when there is leakage flow,especially with the emergence of secondary flow in the upstream cavity.When the leakage flow flows out of the upstream cavity,some moves downstream with the main flow,the other part flows to the corner of the suction surface under the action of transverse pressure gradient,and climbs along the blade after blending with the low-energy fluid in the corner zone,which can affect the flow within the whole blade height range.2.The flow condition in the corner zone is better at the negative angle of attack,when the angle of attack turns to positive,the flow difference of the leakage flow is getting larger,as the angle of attack increases,the proportion of leakage flow relative to the mainstream flow increases linearly,but there is no obvious linear relationship between the total pressure loss of each surface in flow direction,the blade load is the largest at 4° angle of attack and the cascade expansion capacity is the strongest.When the Mach number is between 0.1 and 0.5,the leakage flow structure does not change much,while it turns to 0.7,the secondary flow of the upper end wall is no longer mixed with the leakage flow,and the leakage flow only reaches 70% of the height at the trailing edge.Within a certain range,the increase of the velocity of the lower cavity wall can reduce the influence of the leakage flow to the mainstream,the change of the velocity mainly changes the tangential velocity of the leakage flow in the upstream and downstream cavity,which reduces the mixing loss between the leakage flow and the mainstream at the inlet,and improves the ability to resist the transverse pressure gradient in the channel.3.The direction of the rounding of the upstream cavity outlet has a decisive influence on the flow performance of the cascade,the direction of the opening is consistent with the flow direction,which will aggravate the flow separation,the direction of the opening is opposite to the flow direction,which can improve the flow performance,the total pressure loss of the outlet section can be reduced by 1.38% under the calculation conditions in this paper.The addition of ribs on both side walls of the cavity can reduce the total pressure loss of the S3 section of the whole channel,and the relative position of the ribs has a significant influence,The research shows that when the first layer of ribs is placed on the wall of the hub,the effect is better,and the total pressure loss coefficient of the outlet section can be reduced by 3.49%.