Andrew J. Brune

Uncertainty Analysis of Mars Entry Flows over a Hypersonic Inflatable Aerodynamic Decelerator

A detailed uncertainty analysis for high-fidelity flowfield simulations over a fixed aeroshell of hypersonic inflatable aerodynamic decelerator scale for Mars entry is presented for fully laminar and turbulent flows at peak stagnation-point heating conditions. This study implements a sparse-collocation approach based on stochastic expansions for efficient and accurate uncertainty quantification under a large number of uncertainty sources in the computational model. The convective and radiative heating and shear stress uncertainties are computed over the hypersonic inflatable aerodynamic decelerator surface and are shown to vary due to a small fraction of 65 flowfield and radiation modeling parameters considered in the uncertainty analysis. The main contributors to the convective heating uncertainty near the stagnation point are the CO2–CO2, CO2–O, and CO–O binary collision interactions, freestream density, and freestream velocity for both boundary-layer flows. In laminar flow, exothermic recombination rea...

Uncertainty Analysis of Radiative Heating Predictions for Titan Entry

The objective of this study was to investigate the uncertainty in shock layer radiative heating predictions on the surface of a hypersonic inflatable aerodynamic decelerator during Titan entry at peak radiative heating conditions. Computational fluid dynamics simulations of planetary entry flows and radiative heating predictions possess a significant amount of uncertainty due to the complexity of the flow physics and the difficulty in obtaining accurate experimental results of molecular-level phenomena. Sources of uncertainty considered include flowfield chemical rate models, molecular band emission, and the excitation/deexcitation rates of molecules modeled with a non-Boltzmann approach. Because of the computational cost of the numerical models, uncertainty quantification was performed with a surrogate modeling approach based on a sparse approximation of the point-collocation nonintrusive polynomial chaos expansion. Accurate uncertainty results were obtained with only 500 evaluations of the computational...

Variable transpiration cooling effectiveness in laminar and turbulent flows for hypersonic vehicles

Reusable thermal-protection systems with active cooling, such as transpiration, are among the promising technologies for thermal management of hypersonic vehicles designed as practical, long-range transportation systems. This paper numerically investigates the effectiveness and efficiency of a variable-velocity transpiration technology for fully laminar and fully turbulent hypersonic flows over a two-dimensional blunt leading-edge geometry. For both flow types, variable transpiration based on a sawtooth velocity distribution is compared to a uniform-velocity transpiration approach. An equal amount of coolant has been imposed to compare the cooling effectiveness between two strategies. The results numerically demonstrate the significant reduction in stagnation-point heating and coolant mass savings achievable with the variable-transpiration strategy, which is observed both in laminar and turbulent flows. The transpiration cooling efficiency is shown to be higher in laminar flow compared to turbulent flow d...

Backshell Radiative Heating on Human-Scale Mars Entry Vehicles

This work quantifies the backshell radiative heating experienced by payloads on humanscale vehicles entering the Martian atmosphere. Three underlying configurations were studied: a generic sphere, a sphere-cone forebody with a cylindrical payload, and an ellipsled. Computational fluid dynamics simulations of the flow field and radiation were performed using the LAURA and HARA codes, respectively. Results of this work indicated the primary contributor to radiative heating is emission from the CO2 IR band system. Furthermore, the backshell radiation component of heating can persist lower than 2 km/s during entry and descent. For the sphere-cone configuration a peak heat flux of about 3.5 W/cm was observed at the payload juncture during entry. At similar conditions, the ellipsled geometry experienced about 1.25 W/cm on the backshell, but as much as 8 W/cm on the base at very high angle of attack. Overall, this study sheds light on the potential magnitudes of backshell radiative heating that various configurations may experience. These results may serve as a starting point for thermal protection system design or configuration changes necessary to accommodate thermal radiation levels.

Integrated Analysis of Reusable Thermal Protection Systems Based on Variable-Transpiration Cooling

Reusable thermal protection systems are one of the key technologies that have to be improved to use hypersonic vehicles as practical, long-range, transportation systems. The proposed concept of variable-transpiration cooling is investigated in this work by coupling the hypersonic boundary-layer solution with the thermal response of a porous material. The simulations of the hypersonic boundary layers are obtained using an in-house-developed reduced-order model capable of handling generic injection velocity profiles at the porous wall and the high-fidelity computational-fluid-dynamics code Langley Aerothermodynamic Upwind Relaxation Algorithm. The material thermal response is included adopting a one-dimensional model for the porous medium. The integrated analysis is performed for a flat plate and a two-dimensional blunt-body configuration. A sawtooth wall velocity profile was chosen to represent the variable-transpiration strategy. The uniform transpiration on the blunt body allows for a reduction of the st...

Uncertainty Analysis of Radiative Heating for Multiple Planetary Entry Cases (Invited)

The objective of this study was to investigate the uncertainty in shock layer radiative heat predictions on the surface of a hypersonic inflatable aerodynamics decelerator during Mars and Titan entries at peak radiative heating conditions. Computational fluid dynamics simulations of planetary entry flows and radiative heat predictions possess a significant amount of uncertainty due to the complexity of the flow physics and the difficulty in obtaining accurate experimental results of molecular level phenomena. Sources of uncertainty considered include flow field chemical rate models, molecular band emission, and the excitation/deexcitation rates of molecules modeled with a non-Boltzmann approach. Due to the computational cost of the numerical models, uncertainty quantification was performed with a surrogate modeling approach based on a sparse approximation of the point-collocation nonintrusive polynomial chaos technique. Accurate results were obtained with only 500 samples of the computational model. Baseline results indicated that radiative heating during Titan entry was nearly 10 times greater than that of the predicted radiative heating during Mars entry. These results indicated that worst-case uncertainty intervals of surface radiative heating predictions were as wide as 30 W/cm during Mars entry and 150 W/cm during Titan entry. Global nonlinear sensitivity results show that the contribution of the uncertain parameters to output uncertainty measures changes across the surface during Mars entry, whereas Titan radiation uncertainty is dominated by flow field chemistry uncertainty throughout the flow field.

Thermal Protection System Response Uncertainty of a Hypersonic Inflatable Aerodynamic Decelerator

The objective of this paper is to investigate the uncertainty in the bondline temperature response of a flexible thermal protection system subject to uncertain parameters in the hypersonic flowfiel...