Date of Award

12-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Dr. Richard Miller, Committee Chair

Committee Member

Dr. John Saylor

Committee Member

Dr. Xiangchun Xuan

Abstract

Various types of air breathing engines are used as propulsion devices in aviation. At high flight velocities, the use of a ramjet or supersonic combustion ramjet (scramjet) may be preferred due to the natural compressibility of air at high speed. A scramjet, while similar to the ramjet, does not slow air to subsonic speeds prior to combustion, allowing it to operate at much higher flight velocities at very high altitude. For this reason, however, the residence time of air inside of the combustor is on the order of milliseconds, requiring rapid mixing and ignition of the fuel to generate adequate thrust. To do this, a flameholder is often used, which generates turbulence, shock waves, and maintains a recirculation region through geometric effects. In this study, four geometry types involving eighteen separate designs were chosen and analyzed using CFD software. Isolator inlet Mach numbers of 2.2, 4, 6, 8, and 10 were selected to model varying flight velocity, and hydrogen fuel was injected sonically at all injector locations with a single step reaction mechanism applied for combustion. An existing square cavity model was chosen and modified to produce slanted cavity, double cavity, and combined strut-cavity designs. The flameholders were analyzed in a non-reacting simulation to observe their effects on the flow field and fuel mixing efficiency. Reacting simulations were performed for each flameholder to investigate flame stabilization capabilities, thermal choking, stagnation pressure losses and drag generated inside of the combustor. Results show that all designs sustain a flame during combustion at all flight Mach numbers. However, the square cavity with a back cavity injector does this while limiting losses and drag due to shock wave formation, thermal choking, and geometric effects in the flow.

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