Experimental Study of the Single Expansion Ramp Nozzle Flow Properties and its Interaction with the External Flow

Kurzfassung

In order to save weight and increase the maximum payload of space transportation systems, airbreathing propulsion uses the surrounding air to burn the fuel. Therefore, it is an alternative to the existing rocket propulsion systems, which carry liquid oxygen on board. The aerodynamic stability and providing sufficient thrust are the main problems of a hypersonic vehicle propelled by a scramjet engine. The nozzle flow and its interaction with the external flow have a significant impact on these two problems. 2 For this reason, it is necessary to study the aerodynamic phenomena and their effects on the nozzle performance which are caused by the interaction between the external flow and the nozzle flow. The German research project “Aerothermodynamic Design of a Scramjet Propulsion System for Future Space Transportation Systems” aims to improve the key technologies for the design of a scramjet propulsion unit. The goal of the presented study, that is part of this research project, is to design a scramjet nozzle and carry out an experimental study on its performance. A design tool for single expansion ramp nozzles (SERN), developed at the DLR in Cologne, has been applied for the design process. One of the objectives of the presented study is to gain information about the influence and effects of temperature and viscosity on the aerodynamics of the nozzle and external flow. Therefore, experiments with different nozzle flow temperatures are performed. Pressure measurements and Schlieren photographs give a first idea of the effects and impacts caused by the different nozzle flow temperatures. Besides classical pressure and temperature measurement techniques high-speed Schlieren technique and IR thermography are used for flow visualization and surface heat flux measurements. In addition, the Pressure Sensitive Paint (PSP) method is applied to measure the pressure distribution on the entire expansion ramp of the nozzle. This helps to visualize the pressure distribution on the surface and to qualify the pressure sensitive paint method in hypersonic flow fields. The experiments take place in the H2K wind tunnel facility of the DLR in Cologne. The free-stream Mach number is set to Mach 7 and various Reynolds numbers can be realized in the range from Re = 2.5 x 10/6 to Re = 15 x 10/6 to see the effects of different boundary layer conditions.