Numerical Modelling of Shock Wave Boundary Layer Interactions in Aero-Engine Intakes at Incidence

Abstract

During situations of high incidence, high curvature of aero-engine intake lips can locally accelerate flow to supersonic speeds, producing undesirable shock wave boundary layer interactions (SWBLIs). The present work describes simulations of a novel experimental model resembling a lower intake lip at incidence. RANS, LES and hybrid RANS-LES are carried out at two angles of attack, α = 23° and α = 25°, with α = 25° possessing a high degree of shock oscillation. Modifications to the Spalart-Allmaras (SA) RANS turbulence model are proposed to account for re-laminarisation and curvature. These provide an improvement in prediction compared standard SA model. However, RANS models fail to reproduce post shock interaction flow, giving incorrect shape of the flow distortion. LES and hybrid RANS-LES perform well here, with downstream flow distortion in very good agreement with experimental measurements. LES and hybrid RANS-LES also capture the time averaged smearing of the shock which RANS cannot. However, low frequency shock oscillations in the α = 25° case are costly for LES, requiring long simulation time to obtain time averaged flow statistics. Hybrid RANS-LES offers a significant saving in computational cost, costing approximately 20% of LES.

Areas of Investigation into Air Intake Systems for the Impact on Compressor Performance Stability in Aircraft Turbine Engines

“…However, this curvature causes the sound barrier to be exceeded locally and the formation of a lambda-form shock wave. The resulting disturbance in the form of distortion of the airflow spreading deep into the air flow duct of the turbine engine may lead to unsteady operation of the fan and -in extreme cases -failure of the fan blades, which has been presented by Kalsi and Tucker [12].…”

Eddy Resolving Strategies in Turbomachinery and Peripheral Components

“…ZLES is performed with approximately 14 million grid points and wallresolved LES with 50 million grid points. Full test case details can be found in Kalsi and Tucker [19]. Figure 7 shows Schlieren imaging.…”

“…8, from Ref. [20], lines marked x t are used to identify the onset turbulence transition at this rig scale Reynolds number. As can be seen, the transition location is extremely unsteady.…”

A Wind Tunnel Rig to Study the External Fan Cowl Separation Experienced by Compact Nacelles in Windmilling Scenarios

“…Nevertheless, the precise separation behaviour remain poorly understood due to the complex underlying fluid mechanics, with the external fan cowl boundary layer subjected to strong favourable and adverse pressure gradients in close succession. Furthermore, due to these complexities, the flow field is not reliably computed by the Reynolds-averaged Navier-Stokes (RANS) methods typically used in industry, which is particularly problematic for nacelle designers [6,7]. These difficulties are compounded by a notable lack of high-quality experimental reference data which can be used to validate relevant numerical methods.…”