Numerical study of the ignition dynamics of a base bleed unit during the interior ballistics phase

The aim of this article is to study numerically the ignition dynamics of a Base Bleed (BB) unit during the interior ballistics (IB) phase. A Forward Facing Step case is studied under the physical conditions of the first instants of IB, in order to characterize the convective fluxes at the solid propellant surface of the BB. Large-Eddy Simulations are carried out with the CEDRE CFD code. The recirculation zone obtained in the flow significantly increases convective fluxes at the inlet of the BB channel. The instabilities generated by the recirculation zone have frequencies in line with literature. An unsteady solid propellant ignition model is then presented to take account of BB ignition. A parametric study is carried out to characterize the effect of this model's parameters on ignition time and steady surface temperature. A second case is proposed to study BB ignition in more realistic conditions using a dynamic mesh technique and an unsteady solid propellant ignition model applied to the BB propellant surface. It can be shown that the propellant ignites quicker at the inlet of the BB channel due to higher convective fluxes, corresponding to the location of the recirculation zone. The BB's global ignition time and the mass of propellant burned during the IB phase are then calculated.