Validation of a Numerical Model for Predicting Stalled Flows in a Low-Speed Fan—Part II: Unsteady Analysis

Abstract

This paper investigates the flow near the stall boundary for a low-speed/low-pressure ratio fan. Three-dimensional, Reynolds-averaged Navier–Stokes computations are performed for a modern low speed fan rig for which extensive measured data are available. Simulations are conducted at 80% corrected speed, for which the measured constant speed characteristic contains a part with positive slope. It is shown in this paper that by using an unsteady whole assembly approach, it is possible to predict the flow for all the points on the measured constant speed characteristic (including those on the positive slope part), which is not achievable by using a single passage strategy as it would result in premature “numerical stall.” The results of the computations reveal that for the operating points on the positive slope part of the characteristic, the flow structure becomes asymmetric and hence requires a whole assembly numerical model. The type of asymmetry which appears at lower flow coefficients is similar to the multicell, part span rotating stall, which can occur on the front stages of core compressors at stable operating conditions. The numerical results showed a good correlation with the measured data in terms of stall characteristics.