High resolution schemes for hyperbolic conservation laws

Atomic Spectra Database

The United States has successfully landed five robotic systems on the surface of Mars. These systems all had landed mass below 0.6 metric tons (t), had landed footprints on the order of hundreds of km and landed at sites below -1 km MOLA elevation due the need to perform entry, descent and landing operations in an environment with sufficient atmospheric density. Current plans for human exploration of Mars call for the landing of 40-80 t surface elements at scientifically interesting locations within close proximity (10's of m) of pre-positioned robotic assets. This paper summarizes past successful entry, descent and landing systems and approaches being developed by the robotic Mars exploration program to increased landed performance (mass, accuracy and surface elevation). In addition, the entry, descent and landing sequence for a human exploration system will be reviewed, highlighting the technology and systems advances required.

Mars Exploration Entry, Descent, and Landing Challenges

This report documents the results of a study to address the long range, strategic planning required by NASA's Revolutionary Computational Aerosciences (RCA) program in the area of computational fluid dynamics (CFD), including future software and hardware requirements for High Performance Computing (HPC). Specifically, the "Vision 2030" CFD study is to provide a knowledge-based forecast of the future computational capabilities required for turbulent, transitional, and reacting flow simulations across a broad Mach number regime, and to lay the foundation for the development of a future framework and/or environment where physics-based, accurate predictions of complex turbulent flows, including flow separation, can be accomplished routinely and efficiently in cooperation with other physics-based simulations to enable multi-physics analysis and design. Specific technical requirements from the aerospace industrial and scientific communities were obtained to determine critical capability gaps, anticipated technical challenges, and impediments to achieving the target CFD capability in 2030. A preliminary development plan and roadmap were created to help focus investments in technology development to help achieve the CFD vision in 2030.

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CFD Vision 2030 Study: A Path to Revolutionary Computational Aerosciences

Progress in shock wave/boundary layer interactions

Anew air-radiationmodel is presented for the calculation of the radiative flux from lunar-return shock layers. For modeling atomic lines, the data from a variety of theoretical and experimental sources are compiled and reviewed. A line model is chosen that consists of oscillator strengths from the National Institute of Standards and Technology database and theOpacity Project (formany lines not listedby theNational Institute of Standards andTechnology), as well as Stark broadening widths obtained from the average of available values. Uncertainties for the oscillator strengths and Stark broadening widths are conservatively chosen from the reviewed data, and for the oscillator strengths, the chosen uncertainties are found to be larger than those listed in the National Institute of Standards and Technology database. This new atomic line model is compared with previous models for equilibrium constantproperty layers chosen to approximately represent a lunar-return shock layer. It is found that the new model increases the emission resulting from the 1–6-eV spectral range by up to 50%.This increase is due to both the increase in oscillator strengths for some important lines and to the addition of lines from the Opacity Project, which are not commonly treated in shock-layer radiation predictions. Detailed theoretical atomic bound–free cross sections obtained from the Opacity Project’s TOPbase are applied for nitrogen and oxygen. An efficient method of treating these detailed cross sections is presented.The emission fromnegative ions is considered and shown to contribute up to 10% to the total radiative flux. The modeling of the molecular-band systems using the smeared-rotational-band approach is reviewed. The validity of the smeared-rotational-band approach for both emitting and absorbing-band systems is shown through comparisons with the computationally intensive line-by-line approach. The absorbingband systems are shown to reduce the radiative flux by up to 10%, whereas the emitting-band systems are shown to contribute less than a 5% increase in the flux. The combined models chosen for the atomic line, atomic bound–free, negative-ion, and molecular-band components result in a computationally efficient model that is ideal for coupled solutions with a Navier–Stokes flowfield. It is recommended that the notable increases shown, relative to previous models, for the atomic line and negative-ion continuum should be included in future radiation predictions for lunarreturn vehicles.

Spectrum Modeling for Air Shock-Layer Radiation at Lunar-Return Conditions

An experimental investigation was conducted on a 5-degree half-angle cone and a 5-degree half-angle flared cone in a conventional Mach 6 wind tunnel to examine the effects of facility noise on boundary layer transition. The influence of tunnel noise was inferred by comparing transition onset locations determined from the present test to that previously obtained in a Mach 6 low disturbance quiet tunnel. Together, the two sets of experiments are believed to represent the first direct comparison of transition onset between a conventional and a low disturbance wind tunnel using a common test model and transition detection technique. In the present conventional hypersonic tunnel experiment, separate measurements of heat transfer and adiabatic wall temperatures were obtained on the conical models at small angles of attack over a range of Reynolds numbers, which resulted in laminar, transitional, and turbulent flow. Smooth model turbulent heating distributions are compared to that obtained with transition forced via discrete surface roughness. The model nosetip radius was varied to examine the effects of bluntness on transition onset. Despite wall to total temperature differences between the transient heating measurements and the adiabatic wall temperature measurement, the two methods for determining sharp cone transition onset generally yielded equivalent locations. In the 'noisy' mode of the hypersonic low disturbance tunnel, transition onset occurred earlier than that measured in the conventional hypersonic tunnel, suggesting higher levels of freestream acoustic radiation relative to the conventional tunnel. At comparable freestream conditions, the transition onset Reynolds number under low disturbance conditions was a factor of 1.3 greater than that measured on flared cone in the LaRC conventional hypersonic tunnel and a factor of 1.6 greater that the flared cone run in the low disturbance tunnel run 'noisy'. Navier-Stokes mean flow computations and linear stability analysis were conducted to assess the experimental results and have indicated N factors associated with sharp flared cone transition onset to be approximately a factor of 2 lower than that inferred from the corresponding low disturbance tunnel measurements.

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Boundary Layer Transition on Slender Cones in Conventional and Low Disturbance Mach 6 Wind Tunnels

This paper investigates the non-Boltzmann modeling of the radiating atomic and molecular electronic states present in lunar-return shock-layers. The Master Equation is derived for a general atom or molecule while accounting for a variety of excitation and de-excitation mechanisms. A new set of electronic-impact excitation rates is compiled for N, O, and N2+, which are the main radiating species for most lunar-return shock-layers. Based on these new rates, a novel approach of curve-fitting the non-Boltzmann populations of the radiating atomic and molecular states is developed. This new approach provides a simple and accurate method for calculating the atomic and molecular non-Boltzmann populations while avoiding the matrix inversion procedure required for the detailed solution of the Master Equation. The radiative flux values predicted by the present detailed non-Boltzmann model and the approximate curve-fitting approach are shown to agree within 5% for the Fire 1634 s case.

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Non-Boltzmann Modeling for Air Shock-Layer Radiation at Lunar-Return Conditions

Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.

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Brian R. Hollis

Papers

Spectrum Modeling for Air Shock-Layer Radiation at Lunar-Return Conditions

Boundary Layer Transition on Slender Cones in Conventional and Low Disturbance Mach 6 Wind Tunnels

Non-Boltzmann Modeling for Air Shock-Layer Radiation at Lunar-Return Conditions

X-33 Hypersonic Boundary-Layer Transition

FIRE II calculations for hypersonic nonequilibrium aerothermodynamics code verification: DPLR, LAURA, and US3D