Particle Image Velocimetry on Cork Samples in Arc-Heated Wind Tunnels

Kurzfassung

The high-enthalpy wind tunnel L2K can be used to characterise the impact of dust particles on the recession behaviour of thermal protection systems during Martian entry flight. In the tests, a simplified Martian atmosphere (97% CO2 and 3% N2) is used, and the high enthalpy flow is loaded with micrometric particles of magnesium oxide. Several samples for stagnation point tests made of P50 cork samples from Amorim Cork Composites was positioned inside the particle-laden flow. A 2 dimensions - 2 components particle image velocimetry system was used to measure particle velocity in the free stream of the wind tunnel and in the vicinity of cork samples. Particle velocities ranging from 0 m/s to 2100 m/s are measured and compared with the numerical simulation of the wind tunnel’s particle-free flow. The particle velocity discontinuity across the shock is observed in the PIV results, as well as the counterflow that might be caused by outgassing of cork samples and rebounded particles. Some particles were collected with a cooled probe on the stagnation point and analysed with a Scanning Electron Microscope (SEM) and with Energy-dispersive X-ray spectroscopy (EDX), showing that particles may undergo morphological change depending on the flow condition. A thorough discussion on the hypothesis of particle agglomeration due to melting is reported: suspended particles might melt and agglomerate, depending on the flow’s total enthalpy. The importance of considering this effect for the simulation of atmospheric entry in particle-laden atmospheres is highlighted.