LES of the LS89 cascade: influence of inflow turbulence on the flow predictions

Abstract

Free-stream turbulence preceding high-pressure turbine blades has a crucial impact on blade fields including the heat transfer on the wall. Many parameters characterize this turbulence; its intensity, length scales and physical spectrum are addressed in the study of various operating points of the LS89 configuration. Usually, operating points where weak turbulence is injected are well predicted for all fields by Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). The MUR235 operating point however, with an experimentally injected turbulence level of 6%, remains incorrectly predicted when imposing the experimental values in the simulations. Such difficulties raise many questions amongst which mesh size and turbulent kinetic energy spectrum are of specific importance for LES. Going away from synthetic turbulence injection by imposing a physical energy spectrum can help improving the prediction of heat transfer. From the present study, it seems that turbulent spots developing in a pre-transition region for higher levels of turbulence on the suction side are important features to capture for proper predictions. In parallel, typical structures of boundary layers such as streamwise oriented vortices have been observed and their existence conditions the heat transfer field on the blade wall. From this specific study, all of these physical processes are seen to be highly dependent on the turbulent specification and turbulent transition observed for the MUR235 case. Depending on these inflow specifications, a transitional boundary layer may be encountered upstream of the shock thus modifying the heat transfer profile.

Comparison of Various CFD Codes for LES Simulations of Turbomachinery: From Inviscid Vortex Convection to Multi-Stage Compressor

“…Depending on the code and turbulence injection technique, very different turbulence intensities at the leading edge and turbulence decays are obtained. It is worth explaining at this time that the AVBP computations were run with two injection techniquessynthetic turbulence injection and use of a precursor simulation -and two inlet turbulence intensities -6 % and 18 % [28]. Note that the RANS result obtain with the elsA software, modeled turbulence injected and the transition modeling perfectly match the experiments.…”

Resampling strategies to improve surrogate model‐based uncertainty quantification: Application to LES of LS89

“…Moreover, there is a high level of free-stream turbulence that undergoes stretching around the leading edge of the blade, which modifies the position of the boundary layer transition on the suction side. 46 In the original experiments, 16 an increase in heat transfer is observed on the suction side of the blade when a high turbulence intensity level at the inlet (∼ 6%) as well as a large Reynolds number at the outlet (> 1 · 10 6 ) are present. The simulations recover the shock wave that triggers an abrupt transition of the boundary layer, but turbulent spots may be found upstream of this position that can contribute to the overall heat transfer.…”

The Current State of High-Fidelity Simulations for Main Gas Path Turbomachinery Components and Their Industrial Impact

“…Segui et al [124] compared the properties of inflow turbulence generated either by separate pre-cursor simulations, as used in a number of previous studies [6,50] and synthetic inflow turbulence considered by others (e.g. [101,103]) and found no significant difference in heat flux predictions using either method.…”