Capabilities and limitations of existing hypersonic facilities

This paper presents an overview and analysis of the various aspects of hypersonic ground testing. For this, first the simulation requirements according to the different flow regimes of hypersonics flight are briefly described. Based hereon the methodologies of hypersonic ground testing are reviewed and the limitations of applicability are discussed. The characteristics and capabilities of the different hypersonic wind tunnels which facilitate hypersonic ground testing are discussed. The capabilities and limitations of these facilities are quantitatively assessed in regards to the simulation of relevant flight conditions. In addition, limitations of the ground test facilities, such as test time and test model size, are assessed for reflected shock tunnels and expansion tunnels. The trend is that each type of hypersonic facility has its own unique advantages and disadvantages. Continuous running and blowdown facilities allow the longest running times, detailed measurements and best knowledge of freestream properties, but are limited to low stagnation enthalpies. On the other hand, reflected shock tunnels and especially expansion tunnels allow for high enthalpy conditions, but suffer from short test times and a limited variety of measurement techniques. So, success in experimental hypersonics would result from testing in a variety of different facilities in order to benefit from the advantages of each facility. Testing in shock tubes i.e. behind the incident shock wave is not considered in this paper since this type of experiments is mostly suitable for fundamental shock relaxation studies and not for detailed wind tunnel model testing.