The effect of coupled combustion reaction on conjugate heat transfer in boundary layer of a segregated oxidizer/fuel solid motor

Combustion reaction plays an important role in heat transfer of boundary layer of solid rocket motor. In the present study, a transient numerical model is developed to investigate the influence of coupled combustion reaction on heat transfer in boundary layer of the segregated oxidizer/fuel solid motor (SOFSM). The results show that conjugate heat transfer characteristics of non-reacting flow are distinct from those of the reacting flow with coupled combustion. The reacting flow with coupled combustion renders higher and more homogeneous temperature and velocity compared with the non-reacting flow. Due to the effect of combustion heat release on thermophysical properties of the gas phase species, the heat transfer coefficient and effective thermal conductivity of the reacting flow are much higher than those of the non-reacting flow. When the combustion time increases, the heat transfer coefficients decrease in the reacting and non-reacting flows due to reduced flow velocity and lower O₂ concentration. The Nusselt number (Nu) of the reacting flow is also higher than that of the non-reacting flow. Significant decrease of Nu is found in the non-reacting flow with combustion time. However, the Nu varies very slightly along the flow direction in the reacting flow. As pressure increases from 1.5 MPa to 5.0 MPa, the high-temperature area becomes narrower and the flow velocity decreases in the combustion channel. The diffusion and mixing of the oxidizer and fuel gas along the radial direction are thus weakened in the coupled combustion flow. The total heat transfer coefficient decreases from 295.88 W m⁻² K⁻¹ to 46.52 W m⁻² K⁻¹ and Nu decreases from 36.27 to 16.56 with increase of pressure. The distribution of total heat transfer coefficient is found to be highly synchronous to the distribution of regression rate of coupled combustion process. The distribution of heat transfer coefficient directly affects parallel regression and coupled combustion of the TAGN propellant. The fitting relationship of Nu, i.e., Nu = 0.058Re^0.6Pr^0.424 is obtained for the coupled combustion flow in the motor, which provides better insight into the heat transfer in the SOFSM system.