Modelling supersonic combustion could advance design of scramjets

The processes involved in airflow connected with supersonic flight have been a problem for aerospace engineers for decades. It was working out how to cope with the shockwave of exceeding the speed of sound that was the sticking point for designing the first supersonic aircraft. Today, the difficulty comes more with modelling what happens inside an engine that propels aircraft at supersonic speeds.

In a jet engine, air flow is slowed down to increase the temperature and pressure for combustion to ensure that the correct ratio of fuel to air is maintained to optimise thrust and acceleration. In supersonic engines, the situation is even more complicated, with supersonic shockwaves creating turbulent flow inside the engine with vortices that change the way fuel combusts and multiplies the number of possibilities for the way the particles can behave.

Modelling supersonic flow in an engine is extremely difficult because of the complexity of the situation. "Currently, no commercial software can simulate the supersonic combustion problem because it requires high-order numerical schemes to compute supersonic flows with complicated evolved shocks, as well as corrected models to describe the droplet dynamics, both of which we carefully consider in our in-house simulation codes," said Bing Wang of the School of Aerospace engineering at Tsinghua University in Beijing, a co-author of a study on simulating supersonic air flows in the journal Physics of Fluids. "Direct numerical simulation can capture the full scales of flows involved in the shock-vortex interaction."