Shock induced mixing and combustion in scramjets

Buttsworth, D. R. (David R.) (1994). Shock induced mixing and combustion in scramjets PhD Thesis, School of Engineering, The University of Queensland.

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Author Buttsworth, D. R. (David R.)
Thesis Title Shock induced mixing and combustion in scramjets
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 1994
Thesis type PhD Thesis
Supervisor Dr Richard Morgan
Total pages 278
Language eng
Subjects 0901 Aerospace Engineering
Formatted abstract

Analytical and experimental investigations of shock induced mixing and combustion have been conducted in the present study to determine its usefulness in enhancing mixing and combustion in scramjets.

Analytical techniques were developed to describe the steady interaction of an oblique shock wave and a planar mixing region. Under the assumed conditions, it was ascertained that the trajectory of a shock wave through a mixing region is a function of the Mach number distribution. Typically, when an oblique shock wave enters a region of lower Mach number, the shock and flow deflection angles increase, and the post-shock pressure decreases. Due to the importance of vorticity in mixing problems, an analytical expression for the vorticity jump across the shock wave was also obtained. The analysis shows that to be assured of an amplification of the pre-shock vorticity, the gradients of velocity and density within the mixing region must lie in the same direction. These results have important practical implications for the optimisation of shock induced mixing in scramjets.

To test the analytical techniques and examine shock induced mixing and combustion, a number of experiments were conducted in The University of Queensland T4 shock tunnel facility (at Mach numbers between approximately 5.0 and 6.6), and the University of Oxford gun tunnel (at a Mach number of 7. 1). Planar ducts with central strut injection and a variety of shock inducing wedge angles (0, 5, 10, and 15°) were used in both facilities, and additional shock tunnel experiments were conducted using a complex engineering scramjet configuration.

It was determined that the shock wave-mixing region analysis provided a good prediction of the experimentally observed interaction process. Turbulent fluctuations within the mixing regions caused the shock waves to break up into a number of unsteady paths which persisted into the free stream on the other side of the layers. Using the vorticity analysis, mixing enhancement was predicted since the calculated vorticity amplification was between approximately 100 and 400 % fo r the different shock wave-mixing region interactions. Mixing augmentation through shock wave impingement was observed immediately after shock processing in both the gun tunnel and shock tunnel --, experiments. Shock induced combustion was observed in the complex engineering scram jet model, and in the 1 0° wedge and duct configuration.

From the current research, it is apparent that shock induced mixing and combustion remain attractive possibilities for the enhancement of mixing and combustion in scramjets.

Keyword Airplanes -- Scramjet engines

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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