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research-article

VALIDATION OF A NUMERICAL MODEL FOR PREDICTING STALLED FLOWS IN A LOW-SPEED FAN, PART 1: MODIFICATION OF SPALART-ALLMARAS TURBULENCE MODEL

[+] Author and Article Information
Kuen-Bae Lee

Imperial College London, Mechanical Engineering Department, London SW7 2AZ, UK
klee2@ic.ac.uk

Mark J. Wilson

Rolls-Royce plc, Derby DE24 8BJ, UK
mark.wilson@rolls-royce.com

Mehdi Vahdati

Imperial College London, Mechanical Engineering Department, London SW7 2AZ, UK
m.vahdati@imperial.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4039051 History: Received August 14, 2017; Revised December 13, 2017

Abstract

It was found that the standard Spalart-Allmaras (SA) model implemented in the CFD solver used in this work predicts premature stall, which is in line with the observation of other researchers who use the SA model. Therefore, to improve the prediction of the stall boundary, the standard SA model was modified by scaling the source term in the model based on the local pressure gradient and the velocity helicity of the flow. Furthermore, a generalized wall function valid for non-zero wall pressure gradient was implemented to improve the accuracy of boundary conditions at the solid wall. This work aims to produce a turbulence model which can be used to model the flows near the stall boundary for the transonic fan blades on relatively coarse grids of around 600k points per passage. Initially, two fan blades with different design and operating speeds were used to optimize the new parameters in the modified turbulence model. The optimization was based on improving the correlation between measured and numerical radial profiles of the pressure ratio. Thereafter, steady computations were performed for two other blades (by using the same parameters) and the predictions were compared with the experimental data for all the four fan blades. Numerical results showed a significant improvement over those obtained with the original SA model, when compared against the measured data. Finally, for completeness it was decided to test the performance of the modified model by comparing the result with measured data for a simple canonical case.

Rolls-Royce plc
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