Detached Eddy Simulation Compared with Wind Tunnel Results of a Delta Wing with Sharp Leading Edge and Vortex Breakdown

Abstract

A delta wing configuration with a sweep angle of 65 ° has been investigated numerically by detached eddy simulation and compared to experimental results. In the simulations different refinement settings of the grid as well a s time different time step sizes have been applied in order to reproduce the formation of the primary vortex correctly. For the comparison experimental data is available from steady and unsteady surface pressure measurements, hot wire anemometry and several other measurement techniques. I. Introduction avourable configuration for supersonic aircraft com monly are delta wings. There has been intense work on investigation of the complex flow field around delt a wings during the past decades. Two major projects concerning these flows were the international vorte x flow experiments (VFE) one and two. Both featured experimental as well as computational investigation s of delta wing wind tunnel models providing a larg e database of reference material for validation purposes. In VFE- 2 a delta wing with a sweep angle of 65° was invest igated featuring a sharp and several rounded leading edges 1 , of which only the sharp leading edge has been use d in the present study. In the simulations of the round lead ing edges the challenge is reproducing the correct separation behaviour behind the leading edge in order to achie ve the correct vortical flow field further downstre am. At higher angles of attack another phenomenon becomes present, the two primary vortices break down and thus the character of the flow field downstream of the b reakdown location changes drastically. The present work is focusing stronger on this vortex breakdown than on the flow separation. Thus it is limited to the shar p leading edge, which dictates the position for the separation, sin ce the flow cannot stay attached after passing the edge. Though its position thus is fixed the actual process of separa tion still needs to be handled carefully in the sim ulation, since it prescribes the formation of the vortices building t he fundament for the vortex breakdown. Common eddy viscosity RANS models without extensions for vortical flow usually are not able to reprodu ce these flows with vortex breakdown. Thus for the pre sent study an approach of detached eddy simulation (DES) has been selected. The underlying turbulence model is t he SST model 2 and the grid shield model is standard DES 3 . Several numerical meshes have been used to investigate the solution sensitivity to different refinemen t regions. Also the influence of time step size has been addressed. The simulations are compared with wind tunnel measurement results obtained in the low speed wind tunne l at the Technical University Munich.