Explosion Modelling Case Study

Jesmond Engineering conducted a Computational Fluid Dyamics (CFD) simulation of the combustion of hydrogen in an enclosed duct. 1 hundredth of a second of combustion was split into twenty-thousand parts to provide a highly accurate slow-motion animation of an explosion in its initial stages.

The dynamics of an explosion are very complex and seemingly chaotic. The chemical reactions driving the explosion occur on extremely small length and time scales. This means both the mesh size and timesteps used in the simulation must be sufficiently small to properly capture the processes. Having a fine mesh is particularly crucial at the flame front, but less important in the wake and ahead of the flame. The timestep must be chosen such that the numerical scheme solving the discretized flow equations converges. The challenge was performing an accurate simulation that would not require an unreasonable amount of solving time.

By trialling various solver settings, Jesmond Engineering were able to find an excellent balance between an accurate explosion simulation and the time required to solve the problem. Comparison of the flame shape and recorded pressure against published results showed good agreement with Jesmond Engineering’s approach. As such, we furthered our understanding of combustion modelling and are confident in our ability to accurately simulate similar problems.

To minimize the solve time, Jesmond Engineering configured the simulation to refine the mesh in regions where it was needed, and coarsen the mesh far from the flame front. This meant the solver was not wasting time solving the flow equations in regions where the temperature was roughly constant. The problem was also assumed to be symmetric along the central axis, which halves the potential run time.

CFD analysis of combustion is a powerful alternative to experiments or tests, which may be both difficult to perform and hazardous. A computational approach also allows us to visualise the pressure waves and flame geometry in fine detail.