Session: 31-11 Boundary Layer Dynamics

Paper Number: 153164

Non-Equilibrium Boundary Layers on Fan Blades 

This paper investigates the effect of non-equilibrium boundary layers on the aerodynamics of transonic fans. The investigation uses direct numerical simulation (DNS) and low-order modelling to determine the physical mechanisms driving boundary-layer growth. A previous study showed the trailing edge momentum thickness of low speed compressor blades can be modified by more than 30% by non-equilibrium behavior, highlighting the need to correctly model this behavior, and proposed a modification to a widely used RANS turbulence model that gave improved agreement with DNS data. In a transonic blade row, a second non-equilibrium region is formed as the boundary layer is pushed away from equilibrium by the strong adverse pressure gradient imposed by a shock/boundary layer interaction. A novel DNS test-case is presented that allows the capturing of Reynolds numbers representative of both small and large civil aero-engines. The DNS shows that the presence of a shock/boundary-layer interaction rapidly shifts the equilibrium state of the boundary layer, generating a significant non-equilibrium region where the production of turbulence (and therefore turbulent shear work) rises significantly – accurately capturing this process is important to the prediction of displacement thickness and therefore blockage. The physical mechanisms are shown to be captured by an adapted form of the shear-lag model, calibrated using the DNS data. The model demonstrates the associated impact on the development of the boundary layer and the coupled effect on the fan aerodynamics. The results show that non-equilibrium effects are significant even at engine-scale Reynolds numbers, affecting both deviation and loss. 

Presenting Author: Oliver Jagger Whittle Laboratory

Presenting Author Biography: Oliver Jagger is conducting his doctoral research in transonic fan aerodynamics at the Whittle Laboratory in the University of Cambridge, as part of the Centre for Doctoral Training in Future Propulsion and Power. He completed his undergraduate studies at the University of Cambridge in 2020, and after a spell in Formula One aerodynamics has returned to Cambridge to complete his PhD. His research aims to gain understanding of loss mechanisms associated with non-equilibrium turbulence in transonic blade rows using high fidelity simulation to access the true turbulent phenomena seen in the engine.

Authors:

Oliver Jagger Whittle Laboratory
Yuri Frey Marioni Rolls-Royce Plc
Marcus Meyer Rolls-Royce Deutschland Ltd
Andrew Wheeler Whittle Laboratory