Flow Studies on a Scramjet Isolator with a Diverging Cross-Section Using Schlieren Optics

Paper number

IAC-06-C4.5.05

Author

Mr. Sascha Tietz, University of Stuttgart, Germany

Coauthor

Mr. Jaechul Chun, University of Stuttgart, Germany

Coauthor

Prof. Jens von Wolfersdorf, University of Stuttgart, Germany

Year

2006

Abstract

In the last decades a lot of very powerful cryogenic engines and solid rocket boosters have been developed to increase the payload capacity of the actual launchers. But the possibilities for a further enhancement are limited, even with re-usable staged-combustion cycle engines (SSME) combined with new materials. That is why international and national programs like ASTRA (Engl.: Selected systems and technologies for future launch applications) gather information about future launch systems and technologies. One of the investigated propulsion concepts are hypersonic engines using ambient air and hydrogen in a supersonic combustion.
Due to the major disadvantage of this approach, vehicles using scramjet engines are not operational under a certain flight Mach number, the development is focused on dual mode scramjet engines. At lower Mach numbers they are working like a normal ramjet with a subsonic combustion. If the Mach number increases, the combustion becomes supersonic and the engine is working as a scramjet (supersonic combustion ramjet). In the mode transitions an isolator plays a very important role and it should be long enough to prevent the shockwave from travelling upstream. So there is a certain length to obtain both ramjet and scramjet operation. In studies a good correlation for that length was found for an isolator with a constant cross-section. The use of a diverging duct instead could probably reduce the length of the isolator and is the purpose of the experiments explained in the following paragraphes. 
The existing ITLR supersonic facility uses a screw compressor, which is capable of providing an airflow with a pressure of 10 bar and a mass flow of up to 1,5 kg/s. The air is introduced in the test channel using a Laval nozzle providing a Mach number of 2.0 in the test section. The nozzle is followed by the isolator. For the research on a diverging isolator and to test different isolator lengths, a new channel, consisting of five exchangeable modules, was constructed. Each module is equipped with pressure taps along its x-axis with a distance of 20mm to each other. Furthermore glas windows allow the use of optical measurement techniques like schlieren optics. The pressure profile is used to calculate the boundary layer thickness and to determine the onset of separation. Supported by the flow visualisation using schlieren optics and numerical 2D simulations using FLUENT™ a comprehensive picture of the flow characteristics in a diverging isolator can be obtained.
Thereby the effects of different isolator lengths and opening angles are addressed and pseudo-shock structures in case of boundary layer separation are visualized.

Abstract document

IAC-06-C4.5.05.pdf

Manuscript document

IAC-06-C4.5.05.pdf (🔒 authorized access only).

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