Several problems are encountered when a Scramjet reaches hypersonic flight speeds. One of which is that the flow speed of air through the combustor is of the order of 1-2 milliseconds. There is a very limited amount of time available to mix air with any injected fuel. Efficient mixing is a factor which effects combustion and thrust production.
This Thesis investigates a potential mixing enhancement strategy to improve supersonic combustion at hypersonic flight speeds. Streamwise vortices can be used to mix fluids efficiently in a small time frame.
Oblique fuel injection into a supersonic cross flow creates three dimensional vorticity. The generation of streamwise vortices and their effect on air-fuel mixing was investigated. Computational Fluid Dynamics was used to simulate the aerodynamic conditions of a Scramjet travelling with a cruise speed of Mach 9.
Oblique fuel injection through two differing injector geometries was investigated; square and rectangular (aspect ratio 8:1). The injection was orientated in the streamwise direction at a 45 degree angle of elevation. The high aspect ratio rectangle had the best performance and when compared against the square, resulted in a 157% increase in circulation, a 53% increase in mixing efficiency, a 20% increase in domain penetration and an 18% decrease in stagnation pressure losses.
This rectangular fuel injector geometry was selected and the orientation of injection was then investigated. Streamwise injection was compared to cross stream injection, where the fuel contains a span wise velocity component. The injection was orientated in the streamwise and spanwise direction at 45 degree elevation in each direction. The cross stream injector had the best performance and when compared against the streamwise injector, resulted in a 10% increase in circulation, a 10% increase in mixing efficiency, a 22% increase in stagnation pressure loss and negligible change in domain penetration.