An experimental investigation was conducted on premixed cavity stabilized flames in a high-speed ramjet engine, while varying the mean pressure gradients. The ramjet cavity was designed with a backward-facing step and an aft ramp for flame stabilization in regimes with high Reynolds numbers. To study the effects of mean pressure gradients on the engine performance, the ramjet engine underwent variations in wall geometry to create converging, diverging, and nominal configurations. The reacting flow fields and flame dynamics were captured using high-speed, simultaneous particle image velocimetry (PIV) and chemiluminescence imaging diagnostics. The study found that imposing a larger favorable pressure gradient led to a reduction in the recirculation zone and altered shear layer dynamics, resulting in an increased drag on the cavity. Additionally, a stronger favorable pressure gradient excited a shear layer instability mode with a Strouhal number of St = 0.1. The results from proper orthogonal decomposition (POD) analysis indicate that the instability mode comprised large-scale oscillations occupying the entire cavity flow region, indicating that the excited oscillations were due to a global vortex shedding instability under non-reacting conditions. The findings demonstrate that the mean pressure gradient can significantly influence the performance and stability of the ramjet cavity flame, which is crucial for designing high-speed air-breathing propulsion systems such as dual-mode scramjets.


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Graduation Date





Ahmed, Kareem


Master of Science in Aerospace Engineering (M.S.A.E.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering; Thermofluid Aerodynamic Systems Design and Engineering


CFE0009619; DP0027647





Release Date

May 2026

Length of Campus-only Access

3 years

Access Status

Masters Thesis (Campus-only Access)

Restricted to the UCF community until May 2026; it will then be open access.