Direct Numerical Simulation and Measurements of a Solid Fuel Slab Burner Experiment

Slab burner experiments have become important tools for understanding hybrid rocket fuels due to their optical accessibility, which enables non-intrusive measurements. This study aims to simulate the combustion behavior inside a slab burner using direct numerical simulation (DNS) and compare it to experimental results. In particular, the radiation regime for hybrid rockets is of interest and the applicability of a recently developed extension of Marxman theory to account for the effects of radiation. Polymethyl methacrylate (PMMA) slabs are burned under an oxygen environment with variable oxidizer fluxes. Non-intrusive measurements of regression rate, temperature, and velocity are taken using high-speed and DSLR cameras. The temperature is obtained by using two-color pyrometry (TCP) from high speed camera videos. Image velocimetry, using the pixel intensities from the flame, is used to determine the flow speed above the sample. These results are compared against direct numerical simulations (DNS) using a newly developed computational framework, Ablative Boundary Layers at the Exascale (ABLATE), that is designed to run on a large number of compute cores. Overall agreement between TCP / PIV and the DNS is encouraging, showing the DNS faithfully reproduces trends observed by the measurements. The DNS is further used to explore velocity boundary layer scaling and compare it to the simplified Marxman theory. Results indicate that revised scaling based on a streamwise mass flux and inner scaling provides a promising path for developing new theories for reacting and ablating turbulent boundary layers.