Flow structure in the wake of a space-launcher model with propulsive-jet simulation

Abstract

The flow around a space launcher is dominated by flow separation at the junction between the main body and engine and strongly influenced by the propulsive jet. The flow field is highly unsteady with strong local pressure and temperature loads. To conceive a means of mitigating these effects and allow for smarter launcher designs, a better understanding is necessary. The wake of a generic axisymmetric launcher model with and without afterexpanding propulsive jet was investigated at Mach 2.9, a Reynolds number Re D = 1.3 ⋅ 10 6 (model diameter D), and a nozzle exit velocity of the jet simulation of Mach 2.5. I observed the evolution of the flow and its spectral content with velocity measurements with particle image velocimetry and wall-pressure recordings. Coherent structures were analyzed based on a proper orthogonal decomposition. The propulsive jet has two major influences. First, the turbulent intensities in the shear layer are damped, and the larger structures in the wake contain less turbulent kinetic energy than in the baseline case without propulsive jet. Second, the reattachment process is modified and the wake instability phenomena change accordingly. Without propulsive jet, large-scale separation with reattachment on the nozzle fairing occurs and the low-frequency unsteadiness of the closed separation bubble/recompressionshock system is relevant. This phenomenon only has a minor influence under the influence of the jet plume, where the flow is displaced away from the surface and the reattachment process is incomplete. Here, shear-layer instabilities become more prominent.

Investigation of the base flow of a generic space launcher with dual-bell nozzle

“…Experiments with the same forebody geometry confirmed the two-dimensionality and characterized the boundary layer at the end of the main body [6,8,35]. Axisymmetric models are usually mounted by means of struts [15,31,42] which might disturb the outer flow. However, real space launchers are based on axisymmetric geometries.…”

“…The interaction between the external flow and the structure in the afterbody of a launch vehicle is considered a critical factor. In recent years, many experiments [4,5,11,15,18,31,42,43,49] and computational flow simulations [10,23,28,48,[54][55][56] have focused on the dynamics of the separated / reattached shear layer coming from the end of the main body of a space launcher model. It was shown that the shear layer vortices impinge on the rear end of nozzle fairing for a generic Ariane 5-like geometry.…”