Numerical Study of Deflagration to Detonation Transition Using Obstacle Combinations in OpenFOAM

Deflagration and detonation are the modes of combustion at subsonic and supersonic speed respectively. Detonation is marked by sudden rise in pressure in the flow. In this study, Deflagration to Detonation transition (DDT) is numerically investigated in a homogeneous Hydrogen-air stoichiometric mixture inside a tube of 1m length and 50 mm diameter with obstacles. The two-dimensional compressible Reynolds Averaged Navier Stokes equation is solved using open source deflagration to detonation solver `ddtFoam' at OpenFoam platform. The obstacles here are the obstructions in the flow for turbulence enhancement which results in earlier transition of DDT. Seven different combinations of obstacles (DDT enhancement devices) are used in the study, which are various combinations of orifice plate (rectangular obstacle) and Shchelkin spiral (round obstacle). By assigning appropriate initial and boundary conditions, 2D numerical simulations are performed and compared. Deflagration to detonation transition is observed in the tube at various time and locations depending on obstacle configuration. Pressure, temperature and flame tip location vs. time plots are plotted and it has been observed that DDT transition occurred in all the cases except for empty tube and case with two orifice plates. The detonation velocity is close to the CJ velocity value. Faster transition in DDT was observed in the cases with combination of both the obstacles followed by the cases with single type of obstacle. Therefore, earlier DDT transition results in shorter run-up length which greatly affects the tube length which in turn is an integral part of Pulse Detonation Engine operation.