Computational Fluid Dynamics Simulation of Regression Rate in Hybrid Rockets

Modeling of High Density Polyethylene Regression Rate in the Simulation of Hybrid Rocket Flowfields

“…Indeed, the extension of those models to new motors that can be different in geometry, scale, etc., is hardly possible without the availability of existing experimental data for each motor. For these reasons, there is a renewed interest in the development of more accurate and advanced models based on Computational Fluid Dynamics (CFD) [3][4][5][6][7][8][9][10][11][12][13][14][15] that are capable of representing more accurately the physico-chemical phenomena involved. The numerical modeling of the fluid dynamics and the combustion process in the fuel port area and nozzle of a hybrid rocket is a challenging task as it involves strongly-interacting multiphysics processes such as fluid dynamics, fuel pyrolysis [16,17], atomization and vaporization of the oxidizer, mixing and combustion in the gas phase [11][12][13]18], thermochemical erosion of the nozzle [3,19], particulate formation, and the radiative characteristics of the flame.…”

“…Commercial CFD tools are generally not optimized to this task, as they are typically less flexible for the treatment of fluid/solid boundary conditions, which are typically prescribed as constant temperature or heat flux with no feedback with the mass transfer mechanisms (pyrolysis, sublimation, etc.). To obtain an adequate tool for the analysis of the flowfield of hybrid rocket burning classical non-liquefying fuels, CFD codes should take into account spatially-varying heat flux, surface temperature, and fuel regression rate, realistic surface multispecies mass and energy balances, thermal soak into the fuel grain, radiative energy exchange, and finite-rate Arrhenius kinetics for fuel pyrolysis modeling or, in the case of commercial solvers, a number of user-defined functions need to be built and integrated in the numerical framework [8,14,20]. In the most general case, an in-house code has to be used.…”

“…The in-house computational tool used for the simulations, and its gas-surface interaction capability has been validated for high-speed re-entry flows [24], for the analysis of Hydroxyl-Terminated Polybutadiene (HTPB) fuel grains [3,4,25], and for hybrid rocket nozzle thermal protection systems' ablation [3,19,26]. Recent literature works focusing on HDPE fuel grains in hybrid rockets either used commercial CFD tools with user-defined functions to compute the fuel mass flux as a function of the wall heat flux [8,14] or in-house CFD code [15] with imposed fuel mass flux using the mean regression rates measured during the firing test. Thermal radiation was not taken into account in [14,15].…”

“…Thermal radiation was not taken into account in [14,15]. Interestingly, the work in [8] showed that the regression rate was underestimated by 30% for high-density polyethylene grains when radiative heat exchange was not accounted for. The authors concluded stating that no clear information exists regarding the relative importance of radiative heat flux with respect to the convective one for HDPE grains at relatively low gaseous oxygen mass fluxes.…”

Simulation of Gaseous Oxygen/Hydroxyl-Terminated Polybutadiene Hybrid Rocket Flowfields and Comparison with Experiments

“…Nevertheless, hybrid rocket engine development has not achieved the same level of maturity as solid and liquid traditional systems and requires deeper understanding of the physicochemical phenomena that control the combustion process and the fluid dynamics inside the motor [1][2][3][4][5][6][7]. The knowledge of the complex interactions among fluid dynamics, solid fuel pyrolysis [8,9], oxidizer atomization and vaporization, mixing and combustion in the gas phase [7,[10][11][12], nozzle thermochemical erosion [13], particulate formation, and radiative characteristics of the gas and the flame can only be improved by combined experimental and numerical research activities [6,[14][15][16][17][18][19]. The numerical study of the flow in the combustion chamber and in the nozzle of a hybrid propellant rocket requires the ability to adequately describe the interaction between the reacting flow and the solid surface through suitable gas/surface interaction (GSI) modeling.…”