Density measurements in ballistic re-entry

Abstract

The interdisciplinary application of experimental and numerical methods is the crucial strategy for the profound validation of numerical simulations of complex aerothermodynamic flows. Especially for the design of reusable heat shield materials the reliable re-entry heat flux prediction from numerical simulation methods became important. In this context free flight measurements gained an outstanding position for the validation of theoretical models describing the high-temperature phenomena of thermo-chemically reacting hypersonic flows in interaction with the flight vehicle's surface. This article is devoted to present a global concept for the application of a compact free flight sensor exposed to the extreme thermal environmental condition of a controlled, ballistic re-entry. The validation strategy will be demonstrated for total density measurements proposed for the stagnation point of a re-entry capsule, since the density at the capsule surface reflects sensitively the interaction process of the hot gas and the wall. The partial validation of the aerothermodynamic simulation tool was elaborated for laboratory experiments in the gun-tunnel and shock tube. The measuring principle of the optical density sensor, the Phase-compensated Michelson Interferometer (PMI), will be discussed in detail. Since the feasibility of these measurements are highly dependent on the thermal integration of the sensor, an effective thermal protection concept, based on modern ceramic matrix composite materials and high performance insulations, has been verified in numerical analyses.