Assessment of Wall-Modeled LES for Pre-Swirl Cooling Systems

Although conventional Reynolds-averaged Navier-Stokes (RANS) models of turbulence are generally used for predicting the performance of gas turbine pre-swirl systems, these models are known to have shortcomings. Motivated by the need to predict mixing where cooled-cooling air (CCA) and un-cooled cooling air (UCA) streams are introduced in pre-swirl systems, computational fluid dynamics (CFD) modelling capability is reassessed. An initial study focuses on a normal jet in crossflow (JICF), illustrating some of the shortcomings of a popular Reynolds-averaged Navier-Stokes (RANS) model and the possible advantages and disadvantages of wall-modeled large eddy simulation (WMLES). Pre-swirl system studies focus on a previously investigated low radius feed, direct flow configuration for which measurements and CFD solutions are available, and extend this to consider a mixed feed system. The velocities in the near-jet region of the pre-swirl chamber were predicted differently by unsteady RANS (URANS) and WMLES, however no significant differences were observed closer to the receiver holes. Comparing to measurements shows little overall difference between the models, with similar results to earlier studies. Although no measurements are available for a mixed feed system, comparison of predictions from the two models indicates significant sensitivity and uncertainty involved in these predictions.