Thermal Radiative Simulations and Measurements of a Scramjet Test Rig

Abstract

Thermal radiation is a poorly understood process in scramjet engines, but it may play a significant role in the flow and wall heating of the combustion chamber. However, current simulation methods for predicting the thermal radiation in a flight scramjet combustion chamber have yet to be validated with experiments. An experimental measurement apparatus is placed at the rear exit of the HIFiRE 2 direct-connect rig at NASA's Langley Research Center. An array of photodetectors gather emission in the infrared along several lines of sight across the combustor exit. The fields of view are simulated using a ray-tracing-method program that postprocesses a computational fluid dynamics flowfield simulation of the test rig. The ray-tracing program employs a simplified two-point correlated-k spectral model with spectral model error bars. The predictions show an overlap in sensor and experimental predictions for 13 of 16 photodetectors. Nomenclature A = area, m 2 a = spectral quadrature weight B ν = blackbody intensity, W∕m 2 · Hz · sr c 1 = tuning parameter E = estimated error F = spectrally integrated heat flux, W∕m 2 F ν = spectrally specific heat flux, W∕m 2 · Hz f ν = scattering redistribution function I ν = radiative intensity, W∕m 2 · Hz · sr i = location index j = ordinate index k = frequency index l = spectral quadrature index N = maximum index number n = species index S ν = spectral line strength, 1∕m s = trace location, m T = temperature, K U = spectral uncertainty w = standoff position, m X = mole fraction x = streamwise position, m y = vertical position, m z = spanwise position, m θ = azimuthal angle, rad θ 0 = secondary azimuthal angle, rad κ = extinction coefficient, 1∕m μ = ordinate angle factor relative to path, cosϕ μ 0 = secondary ordinate angle factor relative to path, cosϕ 0 ν = frequency, Hz ξ n = normalized number density σ = standard deviation of extinction coefficient, 1∕m ϕ = vertical angle, rad ϕ 0 = secondary vertical angle, rad Ω = optical scattering angle, rad Subscripts band = number of frequency bands filt = quantity at filter LBL = line-by-line variable max = domain upper limit min = domain lower limit quad = correlated-k quadrature scheme sens = quantity at sensor spec = number of species ν = frequency-specific value 0 = nominal state

Thermal Protection System and Thermal Management for Combined-Cycle Engine: Review and Prospects

“…The Langley Research Center of NASA simulated and measured the thermal radiation of ramjets at high Mach numbers [95]. Thermal radiation is a potential factor influencing the calculation of the flow field and wall temperature in the combustion chamber of a ramjet, as shown in Figure 26 [96], yet there are not sufficient experimental verifications of simulation approaches for thermal radiation.…”