Session: 40-06: Turbine Secondary Flows and Interactions I

Paper Number: 151623

Investigation of the Dynamics of Secondary Flow Vortex Systems in Low-Pressure Turbines Using Direct Numerical Simulation 

Profile losses are the primary source of losses in low pressure turbines. However, in realistic applications, the presence of end walls creates secondary flows that introduce additional losses which also contribute to the overall losses of the turbine quite significantly. These secondary flows, arising from the interaction between the end-wall and the turbine blades, form a vortex system whose overall shape has been well described by numerous numerical and experimental studies. Our study is focused on a state-of-the-art low pressure turbine blade with parallel end-walls. We investigate the receptivity of the blade and the vortex system to homogeneous isotropic free-stream turbulence with both laminar and turbulent boundary layer inflow profiles on the end-wall, for various increasing Reynolds numbers. Turbulent mean velocity profiles are based on experimental measurements, with variations on the inner and outer layer thicknesses. Our simulations are performed with Neko, a framework for high order spectral elements for heterogeneous computing architectures. For cases with free-stream turbulence, inlet turbulence intensity and integral length scale profiles are compared and validated against experimental results. From our fully resolved simulations, proper orthogonal decomposition (POD) is applied to provide an overall picture of the flow and a statistical representation of the flow structures in the entire domain. The behaviour of secondary flows along the blade passage and their dependency on external factors is investigated using extended POD projections on temporal and varying spatial bases. This allows us to bring out temporal and spatial correlations between different areas of the blade passage and shed some more light on the effects of the secondary vortices on the overall flow, with the interactions between the vortex system and the highly unsteady separated flow arising closer to the mid span of the blade. 

Presenting Author: Victor Baconnet FLOW, Department of Engineering Mechanics, KTH Royal Institute of Technology

Presenting Author Biography: Victor Baconnet is a PhD student in Computational Fluid Dynamics at the Royal Institute of Technology in Stockholm, Sweden since 2022. He is working under the supervision of Prof. Dan Henningson on flow/boundary layer stability and transition in low pressure turbines and traditional academic flow cases such as flat plates. His work involves the use of Neko, a novel GPU-accelerated spectral element solver, to which he is also actively contributing.

Authors:

Victor Baconnet FLOW, Department of Engineering Mechanics, KTH Royal Institute of Technology
Martin Karp FLOW, Department of Engineering Mechanics, KTH Royal Institute of Technology
Ardeshir Hanifi FLOW, Department of Engineering Mechanics, KTH Royal Institute of Technology
Davide Lengani UNIGE University of Genoa
Daniele Simoni UNIGE University of Genoa
Dan S. Henningson FLOW, Department of Engineering Mechanics, KTH Royal Institute of Technology