Date of Award

Spring 2003

Document Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

Committee Director

Surendra N. Tiwari

Committee Director

Tajeldin O. Mohieldin

Committee Member

Sushil K. Chaturvedi

Committee Member

Arthur C. Taylor, III


A numerical study is conducted to investigate the mixing, combustion, and flow characteristics of different scramjet-combustor configurations. Three-dimensional models for the combustors have been used. Numerical results are obtained using a finite volume computational fluid dynamics (CFD) code with unstructured grids with sizes between 200,000 and 400,000 cells.

In the first part of the current study, the effects of the side angle of the fuel injectors in both mixing and combustion processes are investigated. Raised (compression) and relieved (expansion) wall-mounted ramps are used with side angles of 0 (unswept), 5, and 10 degrees. Results are obtained for nonreacting flows as well as for reacting flows. Hydrogen is used as the fuel in all reacting cases. It is noted that the side angle highly affects the mixing process. The results show clearly that increasing the side angle of the ramps leads to better mixing and further increase of the angle will slightly improve the mixing rate.

In the second part, two dual-mode scramjet-combustor models are investigated. In the first model, fuel is injected through a single unswept wall-mounted ramp parallel to the airstream. In the second model, fuel is injected behind a rearward facing step normal to the airstream. The effects of the combustor length, the equivalence ratio, the number, and the arrangements of the fuel injectors are investigated. Also, the effect of the initial boundary layer thickness is studied. Results show that improved combustion efficiency is obtained by increasing the length of the combustor. For the same amount of injected fuel, increasing the number of injectors improves the combustion efficiency. Asymmetric flow and significant upstream interaction are seen in the isolator section of the second model when using initial boundary layer at the inlets. Furthermore, high degree of upstream interaction is obtained by increasing the number of injectors.