Virginia Tech Compressor Cascade, comparison of predicted tip gap vortex with experimental data.
All turbulence models are able to reproduce the measured blade loading within the experimental scatter.
The prediction of the flow in the tip gap is improved if Reynolds stress models are used. Especially the mean velocity and the velocity fluctuations show better agreement with experimental data. Nevertheless it is obvious that close to walls, the prediction of secondary velocity as well as Reynolds stresses can still be further improved.
The flow through the low-speed subsonic compressor cascade is a demanding test case for turbulence models. The cascade has been extensively investigated by Muthanna and Tang during their respective PhD times at the Virginia Polytechnic Institute and State University in Blacksburg, Virginia. It is built of GE Rotor B section blades with a chord length and blade height of 254mm staggered at an angle of 56.9°. The focus of the investigation is on the flow through the tip gap of 1.65% blade height and the resulting tip gap vortex. The Mach number is 0.073 and the Reynolds number based on the chord length amounts to 400,000.
We simulated the flow using statistical turbulence models of increasing complexity. These are the Menter SST k-ω linear eddy viscosity model, the Hellsten Explicit Algebraic Reynolds Stress Model (Hellsten EARSM) and the SSG/LRR-ω Differential Reynolds Stress Model of Eisfeld. The latter two models account for all the Reynolds stress tensor components by algebraic relations or by solution of partial differential equations. It could be shown that Reynolds stress models lead to improved prediction of the tip gap flow and the passage vortex. More details on the models, the computational method and the results can be found in the proceedings of the THMT 2012 conference.
Morsbach, C.; Franke, M. & di Mare, F.: Towards the application of Reynolds stress transport models to 3D turbomachinery flows, 7th International Symposium on Turbulence, Heat and Mass Transfer, 2012