Large eddy probability density function (LEPDF) simulations for turbulent reactive channel flows and hybrid rocket combustion investigations.

Abstract

A new numerical simulation methodology, Large Eddy Probability Density Function (LEPDF), and corresponding numerical code have been developed for turbulent reactive flow systems. In LEPDF, large scale of turbulent motion is resolved accurately. Small scale of motion is taken care of by a modified Smagorinsky subgrid scale model. Chemical reaction terms are resolved exactly without modeling. A numerical scheme to generate inflow boundary conditions has been proposed for spatial simulations of turbulent flows. Monte-Carlo scheme is used to resolve filtered PDF (Probability Density Function) evolution equation. The present turbulent simulation code has been successfully applied in the simulations of transpired and non-transpired fully developed turbulent channel flows. It more accurately predicts turbulent channel flows than the existing temporal simulation code with only 27% of the grid size of the temporal simulation code. It has been shown that "Ejection" and "Sweep" are two dominant events in the wall region of turbulent channel flows. They are responsible for about 120% of the total turbulent production. Their interactions have negative contributions to the turbulent production, thereby keeping the total 100%. Counter-rotating vortex is a major mechanism responsible for turbulent production in boundary layer. It has also shown that injection from channel side walls increases the boundary layer thickness and turbulence intensities, but decreases the wall friction and heat transfer. Suction has opposite effects. A state-of-the-art hybrid rocket research laboratory has been established. Labscale hybrid rockets with fuel port diameters ranging from 0.5 to 4.0 inches have been designed and constructed. Rocket testing facilities for routine measurements and advanced combustion diagnosis techniques, such as infrared image technique and gas chromatography, are well developed. A computerized data acquisition/control system has been designed and built. A new Cu⁺⁺ based catalyst is identified which can improve the burning rate of general HTPB based hybrid rocket fuel by 15%. Scale-up principles are developed through a series of experimental testing on different sizes of hybrid rockets. A polymer (rocket fuel) degradation model with consideration of catalytic effects of small concentration of oxidizer near fuel surface is developed. The numerical predictions are in very good agreements with experimental data.