Term of Award

Spring 2022

Degree Name

Master of Science, Mechanical Engineering

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Marcel Ilie

Committee Member 1

Prakashbhai Bhoi

Committee Member 2

Mosfequr Rahman

Abstract

Scramjets are supersonic combustion ramjets where there is no mechanical compressor to compress air for combustion. The technology behind engines flying at supersonic speeds has been explored since 1947. It has been in only recent years where the computational power is great enough to handle the challenges. One main challenge with engines is the problem of efficiency. The research conducted explores the background information of scramjets and significant flow field characteristics to optimize the turbulent mixing efficiency. A computational domain was chosen based on a study that revealed that adding dimpled surfaces upstream of a cavity flame holder would suppress pressure oscillations. Suppressing pressure oscillations causes less damage done to the structure of the scramjet engine and reduce the aeroacoustics generated. The research done intends to optimize the dimple diameter and dimple depth to increase mixing found in the cavity. Eight models were created by increasing or decreasing the dimple diameter from 20 mm and increasing the dimple depth from 6 mm. Each case was simulated at freestream velocities, 25 m/s, 35 m/s, 45 m/s, and 55m/s. The velocity contour and vectors showed that the L/D ratio of less than 10 followed the same characteristics of an open cavity where there are two main recirculation regions found in the cavity. Analyzing the pressure identified that the drag inside of a scramjet engine is less when there are dimpled surfaces. Turbulent eddy dissipation and turbulent eddy frequency confirmed that there were recirculation regions of larger eddies found inside the dimples. The skin friction coefficient revealed that adding dimples, increased flow separation in the cavity close to the trailing edge and adds flow separation or mixing at the dimples. To reduce drag and increase mixing in the scramjet engine case Dia20d10 was chosen. This case showed no apparent effects due to increased freestream velocity along the trailing edge of the cavity and increased mixing at the leading edge.

Research Data and Supplementary Material

Yes

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