Evaluation of Eddy Viscosity Models in Predicting Free- Stream Turbulence Penetration

Turbulence schemes have long been developed and examined for their accuracy and stability in a variety of environments. While many industrial flows are highly turbulent, models have rarely been tested to explore whether their accuracy withstands such augmented free-stream turbulence intensity or declines to an erroneous solution. In the present study, the turbulence intensity of an air flow stream, moving parallel to a flat plate is augmented by the means of locating a grid screen at a point at which Rex=۲.۵×۱۰۵ and the effect on the flow and the near-wall boundary is studied. At this cross section, the turbulence intensity is augmented from ۰.۴% to ۶.۶% to flow downstream. Wind tunnel measurements provide reference bases to validate the numerical results for velocity fluctuations in the main stream and at the near-wall. Numerically, four of the most popular turbulence models are examined, namely the oneequation Spalart-Almaras, the two equation Standard k  , the two equation Shear Stress Transport and the anisotropy multi equation Reynolds Stress Models (RSM). The resulting solutions for the domain are compared to experimental measurements and then the results are discussed. The conclusion is made that, despite the accuracy that these turbulence models are believed to have, even for some difficult flow field, they fail to handle high intensity turbulence flows. Turbulence models provide a better approach in experiments when the turbulence intensity is at about ۲% and/or when the Reynolds number is high.

Keywords:

Free stream turbulence , Turbulence intensity , Turbulence penetration , Turbulence models