With the difficulty and cost of full-scale flight experiments, the design of scramjet engines relies heavily on computational simulations. Radiation may play an important role in wall heating and flow cooling of scramjets. However, very few studies have focused on such. The present analysis is based on three-dimensional turbulent reacting flow simulations of the HyShot II hydrogen fueled scramjet engine running at flight conditions of Mach 7.4. A one-dimensional Discrete Ordinates Method analysis with a narrow band averaged spectral model is employed to determine wall heating and flow cooling from thermal radiation. The one-dimensional Discrete Ordinates Method is verified against a three-dimensional ray tracing method. The radiative species considered are H2O and OH. The radiative heat flux is on the order of 10 kW/m 2 , which is 0.1-0.2% of the total convective wall heat flux. Flow cooling due to radiation is found to be on the order of 2 K. Sensitivity analysis shows that radiation is highly dependent on chamber size, temperature, pressure and radiative species mole fraction. Variations in these factors can explain the differences between previous analyses in the literature that studied hypothetical engines and the current work that models an existing scramjet.
Thermal radiation is a poorly understood process in scramjet engines but may play a significant role in the flow and wall heating of the combustion chamber. Previous work has looked at the HyShot II combustion chamber and found the thermal radiation to be insignificant. The current work considers a combustion chamber similar to the HIFiRE-2 supersonic combustion chamber. The combustion flow is computed using a turbulent RANS fluid code, finding the convective heat flux to be on the order of 1.0 to 3.0 MW/m 2 . The flow-field results are post-processed with a Discrete Ordinates Method radiative heat transfer code using a spectrally resolved narrow-band approximation resulting in a radiative heat flux to the wall of 15 to 56 kW/m 2 . A method of estimating the epistemic uncertainty of the radiative wall heat flux stemming from the uncertainty in the spectral model found the radiative wall heat flux to vary by 11 to 15 %. The cooling of the flow due to radiation is predicted using an uncoupled method. Depending on the individual flow-path, the predicted temperature reduction due to radiation can range from 2 to 245 K. Thermal radiative measurements are obtained in an experimental setup of the HIFiRE-2 engine on the HIFiRE Direct-Connect Rig (HDCR) in theArc-Heated Scramjet Test Facility (AHSTF) at NASA Langley Research Center. An array of photodetectors gathered emission in the infrared along several lines-of-sight across the combustor exit. Predictions of radiation along these same lines are compared to the measurements indicating strengths and weaknesses of the simulation approach.
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
With the difficulty and cost of full-scale flight experiments, the design of scramjet engines relies heavily on computational simulations. Radiation may play an important role in wall heating and flow cooling of scramjets. However, very few studies have focused on such. The present analysis is based on three-dimensional turbulent reacting flow simulations of the HyShot II hydrogen fueled scramjet engine running at flight conditions of Mach 7.4. A one-dimensional Discrete Ordinates Method analysis with a narrow band averaged spectral model is employed to determine wall heating and flow cooling from thermal radiation. The one-dimensional Discrete Ordinates Method is verified against a three-dimensional ray tracing method. The radiative species considered are H2O and OH. The radiative heat flux is on the order of 10 kW/m 2 , which is 0.1-0.2% of the total convective wall heat flux. Flow cooling due to radiation is found to be on the order of 2 K. Sensitivity analysis shows that radiation is highly dependent on chamber size, temperature, pressure and radiative species mole fraction. Variations in these factors can explain the differences between previous analyses in the literature that studied hypothetical engines and the current work that models an existing scramjet.
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