CFD Simulation of Supersonic Combustion and Mixing with Flushwall and Ramp Injection Effects for Scramjet Propulsion

Smyth-Hyde, Levi; Bég, O. Anwar; Bég, Tasveer A.; Leonard, Henry J.; Bhatti, M.M.; Kadir, Ali; Jouri, Walid S.

doi:10.22059/jcamech.2026.417785.1874

CFD Simulation of Supersonic Combustion and Mixing with Flushwall and Ramp Injection Effects for Scramjet Propulsion

Document Type : Research Paper

Authors

Levi Smyth-Hyde ¹

O. Anwar Bég ²

Tasveer A. Bég ³

Henry J. Leonard ⁴

M.M. Bhatti ⁵

Ali Kadir ²

Walid S. Jouri ²

¹ MSc Advanced Mechanical Engineering Program, SEE Building, Salford University, M5 4WT, UK

² Multi-Physical Engineering Sciences Group, Mechanical Engineering Department, Corrosion and Coatings Lab, Room 3-08, SEE Building, University of Salford, Manchester, M54WT, UK

³ Engineering Mechanics Research, Israfil House, Dickenson Rd., Manchester, M13, UK

⁴ Multi-Physical Engineering Sciences Group, Mechanical Engineering Department, Corrosion and Coatings Lab, Room 3-08, SEE Building, University of Salford, Manchester, M54WT, UK.

⁵ Department of Physics, College of Science, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea

10.22059/jcamech.2026.417785.1874

Abstract

Scramjet technology promises to reduce the cost of space access systems by eliminating rocket staging designs to reach orbit which are costly and single use. To date, several Scramjet engine testbeds have been capable of igniting and producing thrust in flight conditions, but these tests are not common. Scramjet propulsion systems are faced with complex flow-physics behaviours that moderate their technological development. The insufficient knowledge available on restricted sonic airflow conditions requires computational methods for accurate predictions prior to flight testing. This article therefore deploys ANSYS FLUENT Computational Fluid Dynamic (CFD) software to analyse supersonic flow characteristics in current scramjet combustor designs. The scope of flow passage optimisation in Scramjets lies primarily with the selected fuel injection methods and in this regard both flush wall (30 degrees and 80 degrees inclination) and ramp injector (12 degrees and 18 degrees inclination) designs are simulated here. Reynolds Averaged Navier Stokes (RANS) computations are described to provide numerical results for high velocity, recirculating flows and static pressure, temperature, velocity, density and hydrogen/water/oxygen mass fraction contours are presented. Detailed mesh designs are included and a grid independence study. The material properties of air and the mixture (hydrogen-air) feature ideal-gas density and Sutherland’s viscosity for heat transfer properties to accurately simulate compressibility effects. A two equation, realizable k-epsilon turbulence model is employed with standard wall treatment, to encompass superior simulated rotational spreading behaviour of the flow. The Turbulent Kinetic Energy (TKE), Energy and Wall Prandtl numbers are set as 1, 0.85, and 0.85 respectively. To model the mixing, heat transfer, and combustion with the realizable k-epsilon model, a volumetric, hydrogen-air mixture Species-Transport model with Eddy-Dissipation turbulence-chemistry interactions is incorporated with turbulent Schmidt number of 0.7 and a Turbulent Dissipation Rate (TDR) of 1.2. Two distinct fuel injection methods are presented in this study- the transverse flush wall injection and the ramp method. The hydrogen fuel is injected through a port with a 2mm cross-sectional area. The ramp injection method is an intrusive fuel injection method which trades thrust potential in the form of pressure losses for good mixing characteristics. The strength of the oblique shockwave that forms is entirely dependent on the inclination of ramp, with greater inclination resulting in a stronger shockwave. The presence of the oblique shockwave further increases the mixing downstream of fuel injection due to the interaction of reflected shockwaves with the fuel and air mixing layer. Similar to the flush wall injectors, both ramp designs feature fuel injection ports of 2mm diameter, where the opening of the injector port is 2mm below the upper trailing edge of the ramp geometry. The 18˚ ramp, due to its high profile, generates strong oblique shockwave formation and enhanced downstream mixing due to increased pressure and temperature due the reflection of the intense oblique shock. The 80˚ flush wall injector features the same general dimensions as the first case at 30˚ inclination but introduces the hydrogen fuel near perpendicular to the airflow.

Keywords

Scramjet propulsion

flush wall

ramp

injectors

mixing

shocks

CFD, combustion

Subjects

Aerodynamics

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