TDLAS-based Investigation On The Vitiation Effects Of Hypersonic Testiong Of Aerothermal Behvaviors

Ground test is an important way to investigate the complex hypersonic flow and to predict hypersonic flights performance. However, for most hypersonic test facilities, especially combustion-heated hypersonic wind tunnel, there exists large amount of steam and carbon dioxide in the test gas, whosecomposition is different from that ofthe clean air, which may cause someunexpected deviationsand results in more uncertainties.In this work, a series of experiments were conducted in a shock tunnel with various strengths of shock wavesas well as mole fractions of contaminations (steam and carbon) to simulatethe related combustion-heated wind tunnel flow conditions. The static temperatures of the nozzle exit flow (Mach6and Mach2.5) and the wedged model flow under groups of conditions are obtained through a tunable diode laser absorption spectroscopy (TDLAS) measurement system.The main results of the work can be summarized as follows:1.A newTDLAS measurement system was developed withthe application background of low temperature detection in order to satisfy the flow requirement. The system was examined to work reasonably at the following conditions:the static temperature is200K-400K; the static pressure is0.05atm-0.1atm; the mole concentration of steam is5%-10%and the absorption length of TDLAS is20cm.2.It was found that for a givendriver/driven pressures ratio, the static temperatures of the Mach2.5nozzle exit flow riseswhen the mole concentration of carbon increases. Such aneffectis not obvious with the mole concentration ofcarbon below30%, beyond whichthe effect can bereadily observed.3.In the test attotal temperature of1200K, the static temperatureof Mach6nozzle exit obtainedthrough TDLAS is higher than that of the predicted value without steam condensation. Whilein the test at the total temperature of1800K, the measured static temperature agrees well with that of the prediction. Therefore the results indicates that steam condensation may occur in thefirstcase, which is responsible for the temperature rising.Furthormore, numerical simulation showsthat the contamination in the testing gas may cause the Mach number lower and the steam condensation results in further reduction of Mach number.4. The vitiation effects depend not only on the fractions of contaminants, but also strongly related to the freestream static temperature as well as the compression process of the model flow. A low temperature incoming flow, with minor compression angle is favorable for less vitiation effects. On the other hand however, if the combined interaction of the flow with the compression wall is so severe that the resulted static temperature is increased to a certain level, an obvious dependence of vitiation effects on the contaminations appears evidently.