Three-dimensional Analysis of the Fluctuating Pressure Field of a Space Launcher Afterbody with Boosters using ZDES

Abstract

The numerical investigation of a high Reynolds number compressible separating reattaching flow around a simplified space launcher afterbody is carried out using Zonal Detached Eddy Simulation (ZDES). The geometry consists of a cylinder extended by another cylinder of smaller diameter for the central body and two side cylinders presenting the same features as those of a launcher booster. Statistical results are compared to those of Weiss et al. on an axisymmetric backward facing step with the same geometric characteristics. It is shown that the presence of side-cylinders significantly affects the base flow of the central body. A specific organisation of the wall pressure is evidenced showing that the mean structure as well as the dynamics of the recirculation zone is highly dependent on the azimuthal angle θ. The mean wall pressure coefficient Cp shows a ‘two-pole’ distribution on the emerging cylinder with maximum values in the plane orthogonal to the side-cylinders while the Cprms exhibits four ‘poles’ at angles π 4 , 3π 4 , 5π 4 and 7π 4 , in opposition to a fully axisymmetric behaviour for both the mean and Root Mean Square quantities. The spectral analysis of the fluctuating pressure signals along the azimuthal direction highlights that the characteristic frequency of the shear layer originating from the separation point of the three-body geometry is increased by a factor of 1.5 compared to that of the axisymmetric case. Finally, the three-dimensional investigation evidences the opposition between a fully axisymmetric organisation of the fluctuating energy and a four-quadrant distribution.