Investigation of Soot Combustion in Underexpanded Jet Plume Flows

Abstract

A new overlay technique to model and simulate the soot combustion in rocket plumes is proposed and examined. An efficient methodology for the accurate prediction of soot oxidation is discussed so that the sensitivity of soot combustion to the complex plume flow characteristics may be better understood. The accurate prediction of soot combustion in rocket plumes affects the plume radiation pattern and the location of the maximum radiation in underexpanded rocket plumes. A continuum approach for the soot overlay problem is presented for the example problem of a single-nozzle axisymmetric plume representative of the Atlas rocket. The overlay calculations are applied to a third-order-accurate converged Navier-Stokes result for a chemically reacting gas flow at the altitudes of 21, 30, and 40 km. Results are presented to demonstrate the sensitivity of soot oxidation to the initial spatial distribution of soot at the nozzle exit plane and the altitude dependence of soot combustion in the plume flowfield for various pressure ratios. It is shown that the majority of the soot combustion occurs in the plume shear layer due to the higher temperatures and penetration of oxygen into the flow. Also, there is more combustion at lower altitudes due to increased availability of oxygen for combustion, even though the shear layer at the lower altitudes is thin.