Session: 32-01 High Fidelity CFD

Paper Number: 121415

121415 - Prediction and Analysis of Turbulence Anisotropy in a Low-Pressure Turbine Cascade at Two Reynolds Numbers Based on Transitional DDES 

This study analyzes the influence of Reynolds number on the turbulence anisotropy behavior for the transitional flow over the MTU-T161 linear low-pressure turbine cascade. Two operating points at Reynolds number Re=90,000 and Re=200,000, both at an isentropic exit Mach number of 0.6, are calculated using a transitional Delayed Detached Eddy Simulations (DDES) model. We focus our investigation on the separation induced transition occurring on the suction side, its sensitivity to the Reynolds number and the capabilities of the transitional DDES approach to capture the turbulent state.

The computational model of the MTU-T161 cascade consists of one blade passage, including the diverging viscous side-
walls. Synthetic turbulence is generated at the inlet of the domain to mimic realistic turbomachinery flow conditions. The utilized DDES method is based on a vorticity-based formulation to calculate the subgrid length scales and it incorporates the one-equation 𝛾-transition model.

We show that the DDES-𝛾 model is able to capture the separation and transition mechanism correctly for both Reynolds numbers, when compared to experimental data. The main part of this paper consists of a detailed analysis of the turbulence anisotropy behavior with particular attention to the separation bubble while changing the Reynolds number. By increasing the Reynolds number from 90,000 to 200,000, the turbulence anisotropy state of the suction side flow changes only slightly which is due to the smaller separation bubble. The turbulence anisotropy analysis reveals a nearly two-component state very close to the wall region and a one-component turbulence state in the separated shear layer for both Reynolds numbers. At Re=200,000, the turbulence state in the free-stream region is governed by two components, while the separation bubble and its influence become weaker. Additionally, we show the capability of the DDES-𝛾 model to capture the correct trend of the Reynolds stresses and the anisotropy behavior by comparing the results to a previously published reference LES.

These results enhance our overall comprehension of the turbulence state and the associated total pressure loss within different separation bubble sizes. Furthermore, the results indicate that the DDES-𝛾 model resolves the essential characteristics of turbulence while keeping the computational cost up to ten times lower than LES. This advantage is especially prominent in higher Reynolds number regimes.

Presenting Author: Nima Fard Afshar Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University

Presenting Author Biography: Nima Fard Afshar is a Ph.D. student at the Institute of Jet Propulsion and Turbomachinery of RWTH Aachen university.
He holds an M.Sc. and BEng. in Aersospace Eng. from Technical university of Braunschweig.
He worked after his MSc. studies for 5 years in the automotive industry dealing with aeroacoustic simulations of turbochargers based on scale resolving CFD.
His research interests are computational fluid dynamics, turbulence, scale resolving simulations and aeroacoustics.
Currently his research focus is to quantify the capability of different scale resolving methods, such as Hybrid RANS-LES, LES and DNS, to analyze the turbomachinery flow in detail.

Authors:

Nima Fard Afshar Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Felix M. Möller German Aerospace Center (DLR), Institute of Test and Simulation for Gas Turbines
Johannes Deutsch Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Stefan Henninger Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Christian Morsbach German Aerospace Center (DLR), Institute of Propulsion Technology
Dragan Kožulović University of the Bundeswehr Munich
Patrick Bechlars MTU Aero Engines AG
Peter Jeschke - Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University