Enhancement of Free Flight Force Measurement Technique for Scramjet Engine Shock Tunnel Testing

Abstract

The free flight force measurement technique is a very attractive tool to determine forces and moments in particular in short duration ground based test facilities. With test times in the order of a few milliseconds, conventional force balances cannot be applied. The free flight technique has been applied in a number of shock tunnels utilizing models up to approximately 300 mm in length and looking at external aerodynamics. Test campaigns in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) conducted in the framework of the EU co-funded LAPCAT II project demonstrated that this technique, in combination with optical tracking, can successfully be applied for thrust measurements of a complex fully integrated scramjet engine. In addition to the engine components intake, combustor and thrust nozzle, the hydrogen fueling system and gauge measurement infrastructure were integrated in the 1.5 m long model with a mass of 85 kg. The test campaigns in HEG together with vehicle aerodynamics predictions based on computational fluid dynamics demonstrated experimentally that the considered small scale flight experiment configuration is able to generate net thrust, i.e., has a positive aero propulsive balance. In the present article, the results of a new HEG test campaign utilizing an optimized optical set-up are presented. Motivated by uncertainty analyses results, the optical resolution and the camera frame rate were increased. It could be shown that by these modifications the uncertainty of the thrust increment measurements could be reduced by a factor of approximately 2. Further, the new results demonstrated the repeatability of the scramjet thrust measurement technique in HEG.