Effect of Different Subgrid-Scale Models and Inflow Turbulence Conditions on the Boundary Layer Transition in a Transonic Linear Turbine Cascade

Ettore Bertolini,Paul Pieringer,Wolfgang Sanz

doi:10.3390/ijtpp6030035

Ettore Bertolini, Paul Pieringer + Show 1 more

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https://doi.org/10.3390/ijtpp6030035

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Abstract

The aim of this work is to study the influence of different subgrid-scale (SGS) closure models and inflow turbulence conditions on the boundary layer transition on the suction side of a highly loaded transonic turbine cascade in the presence of high free-stream turbulence using large eddy simulations (LES) of the MUR237 test case. For the numerical simulations, the MUR237 flow case was considered and the incoming free-stream turbulence was reproduced using the synthetic eddy method (SEM). The boundary layer transition on the blade suction side was found to be significantly influenced by the choice of the SGS closure model and the SEM parameters. These two aspects were carefully evaluated in this work. Initially, the influence of three different closure models (Smagorinsky, WALE, and subgrid-scale kinetic energy model) was evaluated. Among them, the WALE SGS closure model performed best compared to the Smagorinsky and KEM models and, for this reason, was used in the following analysis. Finally, different values of the turbulence length scale, eddies density, and inlet turbulence for the SEM were evaluated. As shown by the results, among the different parameters, the choice of the turbulence length scale plays a major role in the transition onset on the blade suction side.

Highlights

In modern aero engines, the turbine stages have to deal with extreme conditions due to the presence of high pressures, high temperatures, and high levels of turbulence.In order to ensure the performance and the lifetime of the components, precise knowledge and control of the flow field inside the machine is required
In order to prove that the solution had converged, the integral of the convective heat transfer coefficient over a region on the suction side of the blade close to the trailing edge was evaluated over time
Had more subgrid-scale viscosity than wall-adapting local eddy-viscosity (WALE) and SMAG, and this caused a suppression of the laminar-to-turbulent transition on the blade suction side (SS)

Summary

Introduction

The turbine stages have to deal with extreme conditions due to the presence of high pressures, high temperatures, and high levels of turbulence.In order to ensure the performance and the lifetime of the components, precise knowledge and control of the flow field inside the machine is required. The turbine stages have to deal with extreme conditions due to the presence of high pressures, high temperatures, and high levels of turbulence. Critical is the region of the flow closest to the solid surfaces. This region is called the boundary layer (BL), and it is here that viscous effects drive the exchanges of energy and momentum. The ability of the boundary layer to remain attached to the blades in the condition of adverse pressure gradients changes dramatically from laminar to turbulent. The control of the boundary layer becomes essential in modern aero engines where high loads and high efficiency are required from every stage

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