Computational Fluid Dynamics Analysis of a Rocket Nozzle with KNSB Propellant Using ANSYS Fluent

This paper presents a computational fluid dynamics (CFD) investigation of the flow characteristics inside a convergent–divergent rocket nozzle operating with a solid KNSB (potassium nitrate–sugar based) propellant. The objective of the study is to analyse the effect of nozzle geometry on pressure, velocity and temperature distribution during steady-state operation and to validate the theoretical flow behaviour observed in practical solid rocket systems. The simulation is carried out using ANSYS Fluent with a three-dimensional, pressure-based, double-precision solver under inviscid flow assumptions. A hexahedral mesh is generated for the nozzle domain to achieve adequate numerical stability and solution accuracy. Ideal gas properties are assigned to combustion products of KNSB propellant with constant specific heat and defined molecular weight. Boundary conditions are applied at the inlet and outlet to simulate high-temperature propellant gases accelerating through the throat. The results show significant pressure drop and velocity rise across the throat region, confirming conversion of pressure energy into kinetic energy. The increase in velocity is accompanied by a corresponding reduction in static temperature due to expansion of the gas stream. Contours and graphs of pressure, velocity and temperature demonstrate physically consistent behaviour expected from isentropic nozzle theory. Although the residuals do not fully reach strict convergence limits, the obtained solution remains numerically stable and acceptable for qualitative assessment. This study highlights the role of CFD in predicting nozzle flow behaviour and provides a basis for future work involving viscous modelling, mesh refinement and experimental comparison.