Shock tunnel free flight force measurements using a complex model configuration

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 here. The technique has been applied in a number of shock tunnels utilizing models up to approximately 300 mm in length and looking at external aerodynamics. In the present study the technique is applied using a complex 1.5 m long hypersonic integrated supersonic combustion ramjet (scramjet) engine consisting of intake, combustor and thrust nozzle. For this type of engine the design objective is a combustor with efficient mixing and combustion within the shortest possible length, but still robust enough to operate in various operational conditions. In the framework of the EU co-funded project LAPCAT II, a M=7.4 scramjet powered small scale flight experiment (SSFE) configuration was designed. Since free jet testing of the complete combustion flow path is a mandatory step within the design roadmap of future engines, ground based testing of the SSFE engine was conducted in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR). This type of facility allows duplication of flight conditions in excess of M=8. Here tests were performed simulating Mach 7.4 flight conditions in approximately 28 km altitude. The numerically predicted thrust of the engine could be confirmed in HEG by free flight force measurements based on displacement measurements utilizing optical tracking. Combining these experimental results with computed aerodynamic data of the complete SSFE showed that for a selected flight condition a positive aero propulsive balance of the complete configuration could be achieved.