LIF Measurement of Rotational Temperatures Near a Hot Surface Part II: SiC-Disk in a Hypersonic Free Jet

Abstract

The Laser Induced Fluoresence (LIF) spectroscopy is a nonintrusive method to measure temperatures and densities in rarefied flows relevant for reentry simulation of HERMES in wind tunnels. The strong nonequilibrium of rotational and vibrational temperature is due to the rapid expansion in Laval nozzles or free jets and typical for hypersonic wind tunnels. LIF excitation spectra of nitric oxide were measured in hot hypersonic free jet expansions at the DLR Goettingen. The highest flow speeds of 2800 m/s were obtainedby mixing He into the test gas. Downstream in the supersonic flow field two hot disk models were installed, on machined of Cu, one of SiC. By means of the LIF measurements in the free flow and in front of the model surfaces the heat transfer can be examined in detail. It turned out that the accommodation for the rotational energy of the test gas is incomplete. This is relevant for the gas-surface interaction of reentry vehicles.