Scramjet: Hypersonic Combustion, Viscous Heating

Hypersonic Combustion in Scramjet with Viscous Heating, CFD Simulation ANSYS Fluent Training

Description

Hydrogen combustion inside a scramjet engine at hypersonic speed represents one of the most demanding reacting-flow problems in CFD, coupling supersonic compressible flow, finite-rate chemistry, and wall heating within a single transient case.

A scramjet (supersonic-combustion ramjet) has no moving parts — it relies entirely on engine geometry to compress incoming air, inject and burn fuel, and expand the combustion products for thrust. This distinguishes it from a conventional ramjet, which decelerates flow to subsonic conditions before combustion occurs; a scramjet instead sustains supersonic combustion throughout, enabling flight above Mach 5.

The 2D geometry consists of two sections — a lower preheating region and an upper stable-burn region — built in Design Modeler and meshed in ANSYS Meshing using a structured grid of 16,320 cells. Inlet air enters at Mach 6, with the domain initialized at 300 K. At the mid-nozzle location, where the flow decelerates to Mach 1, hydrogen is injected supersonically, triggering combustion within the nozzle.

Methodology

Combustion is modeled using the Species Transport model with its volumetric reaction sub-model, with air treated as an ideal gas so that density responds correctly to the steep temperature rise generated during burning. Turbulence is captured using the standard k-ε model, and the case is solved as transient to resolve the developing flow field and flame structure.

Given the numerically stiff nature of hypersonic reacting flows, first-order discretization schemes and reduced under-relaxation factors are deliberately applied to maintain stable convergence throughout the solution process.

Conclusion

Results include 2D contours and vector fields for pressure, temperature, velocity, Mach number, density, and turbulence intensity. The flow physics follows a clear progression: air enters the domain, decelerates to Mach 1 at the combustion section, then re-accelerates toward the outlet. Combustion drives temperatures beyond 4000 K, with viscous heating clearly visible in the near-wall elements, where high-speed shear converts kinetic energy into heat at the wall surface.