Hybrid RANS-LES Simulation of Turbulent High-Lift Flow in Relation to Noise Generation

Abstract

Turbulence-resolving simulations have been performed using hybrid RANS-LES approaches for the turbulent flow around a three-element high-lift configuration. The main purpose is to explore the effect of some modeling-related numerical aspects on the simulation of resolved velocity and pressure fluctuations as potent noise-generating sources. Along with a presentation of resolved instantaneous and mean flow features, the impact of the time step and the spanwise extent of the computational domain is investigated. It is shown that the temporal resolution and the spanwise extension of the computational domain impose effects not only on the prediction of mean flow, but more significantly on the correlation of resolved turbulent structures, which may consequently affect the accuracy of flow-generated noise properties.

Numerical investigation of the flow dynamics past a three-element aerofoil

“…The spanwise extent has to be large enough to insure that the flow becomes completely decorrelated and is not artificially affected by the periodicity condition. Henning et al (2008) and Nebenfuhr et al (2012) showed that the pressure fluctuations feature a stronger correlation than velocity fluctuations so that the spanwise correlation is a good criterion to assess the spanwise extent of the grid. Spanwise correlation data for pressure fluctuations at the slat cove and the flap upper surface are presented in Terracol et al (2011) who concluded that a spanwise extent of 0.8c slat is necessary to get a proper spanwise decorrelation of the slat cove flow.…”

Hybrid RANS/LES Simulations for Aerodynamic and Aeroacoustic Analysis of a Multi-Element Airfoil

“…7(a) and are located directly downstream of the slat cusp, near the free shear layer and in the gap between slat and wing, respectively. A previous study 36 investigated the impact of the spanwise domain extent and found that, even with a spanwise extent of 0.16C, the spatial correlations were strong. This was blamed partly on the grid resolution in the x − y plane and partly on the sampling locations for the two-point correlations themselves, which are placed in regions of strong flow acceleration in which the flow might undergo relaminarization.…”

“…36 The first Kelvin-Helmholtz instabilities could be observed only at about half the way to the impingement point on the lower wall of the slat trailing edge. This phenomenon was partly blamed on insufficient grid resolution in the x − y plane and partly on the so-called "gray area" problem in hybrid RANS/LES methods.…”

“…In a previous work, 36 computations were made with the HYB0 model on the same geometry, and the importance of the grid resolution in the x − y plane was pointed out in particular. Hence, a refined grid was generated and is used in the present work.…”

“…As mentioned above, previous simulations show strongly delayed instabilities of the free shear layer detaching from the slat cusp. 36 Hence, particular attention was paid to the treatment and development of that shear layer. Figure 8 displays a comparison of modeled and resolved shear stresses, u ′ n u ′ s , for Case1 and Case2.…”