A computational fluid dynamics model of combustion of nanoaluminum–water propellant strands

A computational fluid dynamics model of combustion of nanoaluminum–water propellants is developed. An unsteady and axisymmetric model of strand combustion is developed to mimic the experimental setup and conditions. The entire time evolution of strand combustion from ignition until steady-state flame propagation through the strand is simulated. A multiphase Eulerian modeling approach is adopted to handle multiple phases and the associated transport processes. The mass, momentum, species, and energy conservation equations are discretized using the Finite Volume Method. A rigorous computational framework with superior accuracy and stability characteristics is developed and implemented. The theoretical and computational framework is first verified and validated by running standard test cases such as Stefan problem, fluidized bed, and constant-volume reactor. Upon verification and validation, the framework is applied to simulate combustion of stoichiometric nanoaluminum–water propellant strands. The particle size is chosen to be 80 nm and pressure range is taken as 1–10 MPa. The temporal evolutions of flow, temperature, and species composition fields are computed and insights into the underlying physicochemical processes are provided. Measurable quantities such as the burning rate and pressure exponent are computed. Both fixed bed and moving bed combustion scenarios are simulated and the effects of particle retainment in the propellant bed and particle agglomeration are studied. It is found that the multiphase flow dynamics strongly affect the burning rate and its pressure exponent. The present study suggests that the combustion of nano-aluminum and water propellants is diffusion-controlled due to agglomeration of particles.

Novelty and significance statement

A novel theoretical and computational framework is developed to simulate nano-aluminum and water propellant strand combustion. In a paradigm shift in the modeling and simulation approach, a Computational Fluid Dynamics (CFD) approach is adopted to simulate strand burning experiments as closely as possible. A comprehensive multiphase model is developed to resolve all underlying physiochemical processes including boiling of liquid water, multiphase flow dynamics, chemical reactions, and thermal transport. The entire time evolution from ignition until steady-state flame propagation is simulated for an axisymmetric propellant strand. The study provides new insights on the underlying processes that occur during the entire time history of propellant combustion. The simulations demonstrate the importance of multiphase flow dynamics and its impact on propellant combustion. It is discovered that the pressure dependence of burning rate of nano-aluminum and water propellant is primarily due to multiphase flow dynamics and that the combustion of nano-aluminum and water propellants is diffusion-controlled due to agglomeration of particles.