Reacting Flow: Hypersonic Combustion in Scramjet with Viscous Heating

This project simulates hydrogen combustion inside a scramjet engine at hypersonic speed — one of the most demanding reacting-flow problems in CFD, coupling supersonic compressible flow, finite-rate chemistry, and wall heating in a single transient case. A scramjet (supersonic-combustion ramjet) has no moving parts: it relies entirely on the engine geometry to compress incoming air, inject and burn fuel, and expand the products for thrust. The distinction matters — ramjets decelerate flow to subsonic before burning, while a scramjet keeps combustion supersonic, enabling flight above Mach 5.

The methodology combines several physics layers. Combustion is modeled with the Species Transport model and its volumetric reaction sub-model, with air treated as an ideal gas so density responds correctly to the steep temperature rise during burning. Turbulence uses the standard k-ε model, and the case is solved transient to capture the developing flow and flame. Because hypersonic reacting flows are numerically stiff, first-order discretization and reduced under-relaxation factors are used deliberately to hold convergence stable.

Setup: the 2-D geometry has two sections — a lower preheating region and an upper stable-burn region — built in Design Modeler and meshed in ANSYS Meshing as a structured mesh (16,320 cells). Inlet air enters at Mach 6 with the domain initialized at 300 K. At the mid-nozzle, where the flow decelerates to Mach 1, hydrogen is injected supersonically, triggering combustion in the nozzle.

What the results show: 2-D contours and vectors of pressure, temperature, velocity, Mach number, density, and turbulence intensity. The flow physics reads clearly — air enters, slows to Mach 1 at the combustion section, then re-accelerates toward the outlet. Combustion drives the temperature past 4000 K, and viscous heating is visible in the near-wall elements, where high-speed shear converts kinetic energy into heat against the wall.

You'll learn to: set up a transient supersonic reacting-flow case, configure Species Transport with volumetric reactions and ideal-gas density, inject fuel into a Mach-1 region to initiate combustion, and stabilize a stiff hypersonic solution through discretization and relaxation control.