Aerodynamic forces of interacting spheres representative of space debris re-entry: Experiments in a supersonic rarefied wind-tunnel

Experimental investigations of two interacting spheres were carried out in a Mach 4 flow with a static pressure of 2.666 Pa. This study was performed in the MARHy wind tunnel, an adjustable supersonic or hypersonic low-density facility. The main purpose is to estimate how the interactions between spherical debris modify the aerodynamic forces during their atmospheric entry. Indeed, around 80 km, altitude experimentally reproduced thanks to MARHy flow conditions, most debris fragment. The multiple debris, resulting from fragmentation, interact with each other's, which may impact their trajectory. The purpose of this work is to analyze the behavior of a moving sphere placed in the wake of another one. The moving sphere is suspended with two thin wires, so it can almost freely move in the flow direction and physically respond to the acting flow forces of the wake of the first one. Aerodynamic forces are then calculated from the sphere angle deflection. The qualitative analysis of the experimental results will be discriminated first with respect to the trajectory of the second sphere, and secondly with respect to the evolution of the aerodynamic forces according to the sphere.