Reynolds Sensitivity of the Wake Passing Effect on a LPT Cascade Using Spectral/hp Element Methods

Spencer J Sherwin,Raul Vázquez Díaz,Andrés Mateo Gabín,Andrea Cassinelli,Francesco Montomoli,Paolo Adami

doi:10.3390/ijtpp7010008

Abstract

Reynolds-Averaged Navier–Stokes (RANS) methods continue to be the backbone of CFD-based design; however, the recent development of high-order unstructured solvers and meshing algorithms, combined with the lowering cost of HPC infrastructures, has the potential to allow for the introduction of high-fidelity simulations in the design loop, taking the role of a virtual wind tunnel. Extensive validation and verification is required over a broad design space. This is challenging for a number of reasons, including the range of operating conditions, the complexity of industrial geometries and their relative motion. A representative industrial low pressure turbine (LPT) cascade subject to wake passing interactions is analysed, adopting the incompressible Navier–Stokes solver implemented in the spectral/hp element framework Nektar++. The bar passing effect is modelled by leveraging a spectral-element/Fourier Smoothed Profile Method. The Reynolds sensitivity is analysed, focusing in detail on the dynamics of the separation bubble on the suction surface as well as the mean flow properties, wake profiles and loss estimations. The main findings are compared with experimental data, showing agreement in the prediction of wake traverses and losses across the entire range of flow regimes, the latter within 5% of the experimental measurements.

Highlights

In a gas turbine engine, the pressure expansion through high- and low-pressure turbines (LPT) is achieved in a number of subsequent stages
The time averaging operation masks the wealth of flow phenomena occurring in the boundary layer (BL) of LPTs subject to incoming disturbances, and it fails to highlight the presence of high-amplitude events that precede the onset of turbulence
A discussion on some instantaneous flow statistics is presented before analysing timeaveraged statistics, to highlight some of the flow phenomena occurring on the suction surface of the cascade

Summary

Introduction

In a gas turbine engine, the pressure expansion through high- and low-pressure turbines (LPT) is achieved in a number of subsequent stages. One of the early computational investigations of the wake-passing effect was carried out by Wu and Durbin [1,2], who presented evidence that incoming wakes are responsible for the formation of longitudinal structures on the pressure side. A number of Direct Numerical Simulation (DNS) studies were performed on LPTs, providing further contributions to the understanding of the effect of incoming wakes on the pressure- and suction-side boundary layers [3,4,5,6]. A detailed review by Hodson and Howell [7] summarises the wake-induced boundary layer transition mechanisms in LPTs. The impact of the wake passing frequency on loss mechanisms has been numerically investigated by several authors. Michelassi et al [8] built on top of previous work [9]

Methods

Results

Conclusion