Research areas

Computational fluid dynamics

Direct numerical simulation of turbomachinery flows

Overview

Simulating turbomachinery flows using high-fidelity computational methods.

One of the greatest challenges to modern computational fluid dynamics (CFD) is to fully simulate the turbulent flow within an aero engine. Within the engine there are strong interactions of stationary and rotating blades which create a highly unsteady and nonuniform flow field that cannot be simulated correctly with current turbulence models. This is important because unsteadiness and turbulence affects both the aerodynamic efficiency and the heat transfer from the gas to the metal components; the life of the turbine blades is determined by the heat-load which is very sensitive to turbulent convection. Experimental measurements of turbulence properties within the engine are also very difficult to achieve due to the complexities of performing fast-response measurements within engine-scale experimental rigs. 

Improving modeling methods is vital for the future design of more efficient aero engines with increased aerodynamic performance and durability. Up to now, fully resolving the turbulence and unsteady flow field through Direct Numerical Simulation (DNS) has been prohibitively expensive due to the requirement to resolve the very large range of temporal and spatial scales in the flow. This paradigm is now beginning to change due to the development of massively parallelizable codes in combination with large-scale computing hardware, which is enabling the use of high-order direct simulation of turbulence at engine-scale conditions.

DNS gif

Code development

In order to perform high fidelity simulations we have an in-house high order code (3DNS) which has been specifically developed for turbomachinery flows.

People

Publications

Desktop DNS : an open toolkit for turbomachinery aerodynamics

The prevailing view is that high fidelity simulation, particularly DNS (direct numerical simulation), is not something for the practical turbomachinery aerodynamicist — requiring too much computational and personal effort to make it worth it. The aim of the ‘Desktop-DNS’ toolkit described in this paper is to change this by greatly lowering the barrier to entry for running DNS. The paper shows how, using an efficient high-order Navier-Stokes computer code, it is becoming increasingly possible to solve testcases of industry relevance with high fidelity LES and DNS, making use of the latest advances in single compute node performance. This is achievable using both efficient algorithms and GPU acceleration. The paper will use a compressor blade testcase to illustrate how, in some cases, high-fidelity simulations can be performed at relatively low costs on a small number of computer nodes. This raises the possibility of a much more widespread use of DNS to inform early design choices, enhan

Authors:

Andrew P. S. Wheeler

Publication:

Proceedings of the ASME Turbo Expo 2023

DOI:

doi.org/10.1115/GT2023-102647

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Importance of Nonequilibrium Modeling for Compressors

This paper investigates the importance of nonequilibrium boundary-layer modeling for three compressor blade geometries, using RANS and high-fidelity simulations. We find that capturing nonequilibrium effects in RANS is crucial to capturing the correct boundary-layer loss. This is because the production of turbulence within the nonequilibrium region affects both the loss generation in the nonequilibrium region, but also the final equilibrium state. We show that capturing the correct nonequilibrium behavior is possible by adapting industry standard models (in this case the k-omega SST model). We show that for the range of cases studied here, nonequilibrium effects can modify the trailing-edge momentum thickness by up to 40% and can change the trailing-edge shape factor from 1.8 to 2.1.

Authors:

Spencer, Robert ; Przytarski, Pawel; Adami, Paolo

Publication:

Journal of Turbomachinery

DOI:

DOI10.1115/1.4054813

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Unsteady Structure of Compressor Tip Leakage Flows

Direct numerical simulations (DNS) are performed of a cantilevered stator blade to identify the unsteady and turbulent flow structure within compressor tip flows. The simulations were performed with clearances of 1.6% and 3.2% of chord. The results show that the flow both within the gap and at the exit on the suction side highly unsteady phenomena controlled by fine-scale turbulent structures. The signature of the classical tip-leakage vortex is a consequence of time-averaging and does not exist in the true unsteady flow. Despite the complexity, we are able to replicate the flow within the tip gap using a validated quasi-three-dimensional (Q3D) model. This enables a wide range of Q3D DNS simulations to study the effects of blade tip corner radius and Reynolds number. Tip corner radius is found to radically alter the unsteady flow in the tip; it affects both separation bubble size and shape, as well as transition mechanisms in the tip flow. These effects can lead to variations in tip ma

Authors:

Maynard, JM ; Wheeler, APS ; Taylor, JV ; Wells R

Publication:

Journal of Turbomachinery

DOI:

DOI10.1115/1.4055769

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