Time Transformation Simulation of 1.5 Stage Transonic Compressor

Abstract

The accurate prediction of the aerodynamic and aeromechanical performance in a modern transonic compressor often exceeds the capability of traditional steady state mixing plane simulation methods. Time accurate transient blade row simulation approaches are required when there is a close coupling of the flow between the blade rows, and for fundamentally transient flow phenomena such as aeromechanical analysis including blade flutter and forced response, aerothermodynamic analysis and aero-acoustic analysis. Transient blade row simulations can be computationally impractical when all of the blade passages must be modeled to account for the unequal pitch between the blade rows. Most turbomachines consist of multiple stages, further exacerbating the computational challenge. In order to reduce the computational cost, time accurate pitch-change methods are utilized so that only a sector of the turbomachine (one or few passages per row) is modeled. The extension of the time-transformation pitch-change method to multistage machines has recently shown good promise in predicting both aerodynamic performance and resolving dominant blade passing frequencies for a subsonic compressor, while keeping the computational cost affordable. In this work, a modified one and a half stage Purdue transonic compressor (modified for unequal pitch for all three blade rows) is examined. The goal is to assess the ability of the multistage time-transformation method to accurately predict the aerodynamic performance and transient flow details in the presence of transonic blade row interactions. The results from the multistage time-transformation simulation are compared in detail with a transient full-wheel simulation, a profile transformation simulation, as well as to a steady-state mixing-plane model. Flow details are examined including an FFT analysis of select signals, and the onset of stall is compared between all methods. The relative computational effort is compared between all of the analysis methods.