Numerical investigation of the minimum coolant injection rate for transpiration cooling

An advanced design of transpiration cooling system is not only to ensure thermal protection of propulsion system from ablation, but it also should utilize the full temperature potential of porous matrix. A numerical investigation of transient processes of transpiration cooling and the control parameters of the lowest limit of the coolant mass flow rate is conducted with the help of a compressible, unsteady and local non-thermal equilibrium model. The numerical investigation presents that it is important to study transient cooling process, because the porous matrix could be ablated before the cooling process reaches a steady state, though the steady temperature may be lower than the melting point. A higher initial temperature and a larger characteristic size of the porous matrix will result in an increase in the minimum coolant injection rate to prevent ablation of the porous matrix. From the view point of cooling effect, a higher porosity corresponds to a larger coolant mass flow rate. Contrarily, a higher thermal conductivity of the porous matrix corresponds to a lower demand for the minimum coolant flow rate.