Study of Steady State and Transient Blade Row CFD Methods in a Moderately Loaded NASA Transonic High-Speed Axial Compressor Stage

Abstract

The effect of blade row interaction and hub leakage flow on the performance of moderately loaded NASA transonic hybrid compressor stage (Rotor 35 / Stator 37) is investigated through three-dimensional steady state and time-accurate, Navier Stokes calculations of the stage using the ANSYS CFX code at peak efficiency and near stall operating conditions. Understanding unsteady flow phenomena in compressor stages requires the use of time-accurate CFD simulations. Due to the inherent differences in blade counts between adjacent blade rows, the flow conditions at any given instant in adjacent blade rows differ. Depending on the blade counts, it may be necessary to model the entire annulus of the stage; however, this requires considerable computational time and memory resources. Several methods for modeling the transient flow in turbo machinery stages which require a minimal number of blade passages per row, and therefore reduced computational demands, have been presented in the literature. Recently, some of these methods have become available in commercial CFD solvers. The paper describes the steady and the unsteady CFD approaches used for investigating the ability to predict the measured performance of the NASA transonic axial stage design known as the hybrid stage, which consists of the axial Rotor35 and the axial stator 37. The steady approach employs the mixing-plane while the unsteady approaches are URANS with one based on full annulus simulation for the stage and the second enables simulations for the stage using reduced computational model, with a single passage from each blade row based on the time-tilting or the time-transformation technique. The above methods are evaluated and compared in terms of computational efficiency and comparison is made to steady stage simulations. Comparisons to overall performance data and two-dimensional Laser Doppler Velocimeter measurements of the velocity field are used to assess the predictive capabilities of the methods. Computed flow features are examined, and compared with reported measurements. This paper presents validation and calibration of methods used for determining blade row interactions and the respective predictive capabilities against the full annulus and the experimental test data.