Method for Predicting Choke Flow in Vaned Radial Diffusers Based on Thermodynamic and Gas Dynamic Criteria

Conventional vaned diffusers have the disadvantage of extremely high total pressure losses in the region of choke, resulting from channel constrictions in the diffuser cascade. This effect is closely related to increasing impeller tip Mach numbers M_u,² or increasing diffuser inlet flow Mach numbers. This aspect demands very special attention in diffuser design. On the basis of experimental and theoretical studies a hypothetical description of flow conditions within the diffusor was undertaken. The key feature of the working hypothesis is a one-dimensional loss model which is formulated in terms of thermodynamic and gas dynamic relationships. In conjunction with an appropriate application of the laws of conservation, this formulation leads to a method of solution for determining the aerodynamic conditions at the choke condition. Moreover, the method of analysis presented here is also applicable to a wide range of problems in fluid dynamics. In view of the fact that the position of the compressor choke flow rate is physically defined at the cascade inlet and the minimum cascade crossection, this work concentrates thematically on the formulation of the state variables at these locations. The method of analysis was illustrated by way of examples, and the theoretical approach was verified on the basis of experimentally determined flow conditions at choke flow rate.