Rotating Detonation Engine (RDE) is a pressure gain combustion device that works on the detonation mode of combustion. In RDE, a continuous detonation wave travelling within the annular region of two solid cylinders detonates fuel–air mixture entering the chamber to produce near constant thrust by the outflow of burnt gases. The interest in such system is due to greater fuel efficiency offered by detonations in comparisons with deflagrations. Detonations are highly transient in nature, hence the operation of RDE is limited by several types of instabilities associated with the flow field of travelling detonations. Growth of these instabilities is supposed to be function of operating conditions such as fuel–air inflow, working temperature, pressures or engine dimensions. To understand the dynamics of instabilities and study the flow field, numerical simulations are required. For this purpose, an open source numerical solver called ddtFoam is adapted and modified. Available solver was used to study deflagration to detonation in long tubes which was modified for initiating the detonation from a blast region. Modified solver is validated against theoretical calculations and results from other computational fluid dynamics code. Then 3D validation is performed against published reports. Initial results of the simulation are presented here.