Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SHOCK LAYER”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

An approximate viscous shock layer technique for calculating nonequilibrium hypersonic flows about blunt-nosed bodies

An approximate axisymmetric method has been developed which can reliably calculate nonequilibrium fully viscous hypersonic flows over blunt-nosed bodies. By substituting Maslen's second-order pressure expression for the normal momentum equation, a simplified form of the viscous shock layer (VSL) equations is obtained. This approach can solve both the subsonic and supersonic regions of the shock layer without a starting solution for the shock shape. This procedure is significantly faster than the parabolized Navier-Stokes and VSL solvers and would be useful in a preliminary design environment. Solutions have been generated for air flows over several analytic body shapes. Surface heat transfer and pressure predictions are comparable to VSL results. Computed heating rates are in good agreement with experimental data. The present technique generates its own shock shape as part of its solution, and therefore could be used to provide more accurate initial shock shapes for higher-order procedures which require starting solutions.

Cheatwood, F. M.↗
NASA NTRS1989

Titan atmospheric composition by hypervelocity shock layer analysis

The Cassini Mission, a NASA/ESA cooperative project which includes a deployment of probe into the atmosphere of Titan, is described, with particular attention given to the shock radiometer experiment planned for the Titan probe for the analysis of Titan's atmosphere. Results from a shock layer analysis are presented, demonstrating that the mole fractions of the major species (N2, CH4, and, possibly Ar) in the Titan atmosphere can be successfully determined by the Titan-probe radiometer, by measuring the intensity of the CN(violet) radiation emitted in the shock layer during the high velocity portion of the probe entry between 200 and 400 km altitude. It is shown that the sensitivity of the CN(violet) radiation makes it possible to determine the mole fractions of N2, CH4, and Ar to about 0.015, 0.003, and 0.01, respectively, i.e., much better than the present uncertainties in the composition of Titan atmosphere.

Nelson, H. F.↗
NASA NTRS1976

An algorithm for selecting a radiation transport subgrid for ablation and radiation coupled hypersonic viscous shock-layer problems

An algorithm is described for selecting a grid subset for calculating radiative transport. The subset spacing is determined by using the variation in aerothermal properties across the full grid of the shock layer. Results show that a radiation grid subset of 15 to 20 points can be used for viscous-shock layer calculations where approximately 50 grid points are required to define the aerothermal profiles. Results are presented for various planetary entry conditions with and without mass injection to demonstrate both the validity and utility of the algorithm.

Bolz, C. W., Jr.↗
NASA NTRS1991

A shock-layer theory based on thirteen-moment equations and DSMC calculations of rarefied hypersonic flows

Grad's thirteen-moment equations are applied to the flow behind a bow shock under the formalism of a thin shock layer. Comparison of this version of the theory with Direct Simulation Monte Carlo calculations of flows about a flat plate at finite attack angle has lent support to the approach as a useful extension of the continuum model for studying translational nonequilibrium in the shock layer. This paper reassesses the physical basis and limitations of the development with additional calculations and comparisons. The streamline correlation principle, which allows transformation of the 13-moment based system to one based on the Navier-Stokes equations, is extended to a three-dimensional formulation. The development yields a strip theory for planar lifting surfaces at finite incidences. Examples reveal that the lift-to-drag ratio is little influenced by planform geometry and varies with altitudes according to a 'bridging function' determined by correlated two-dimensional calculations.

Cheng, H. K.↗
NASA NTRS2008

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

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.

Johnston, Christopher O.↗
NASA NTRS1994

Viscous Shock-Layer Analysis of Two-Dimensional and Axisymmetric Flows

Results are obtained for cylindrical leading edges of proposed transatmospheric vehicles by employing a two-dimensional viscous shock-layer code for nonequilibrium gas flows. The accuracy and efficiency of the planar code is verified through detailed comparisons with other predictions. This study includes results for 6-deg half-angle bodies with nose radii ranging from 0.01 to 2.0 ft for both cylindrically blunted wedges and spherically blunted cones (included for comparison). Some results are presented as a ratio of the noncatalytic to the corresponding fully catalytic heating value to illustrate the maximum potential for a heating reduction in dissociated nonequilibrium flows. Generally, this ratio and the individual heating rates are smaller for cylindrically blunted wedges with small nose radii as compared to the spherically blunted cones (for the same nose radius). Therefore, a larger potential exists for heating reduction in cylindrically blunted as compared with the spherically blunted surfaces. However, the results presented at higher altitudes (where the slip effects become important) show that the spherically, blunted nose gives lower stagnation-point heating due to stronger merged shock-layer effects as compared with a cylindrically blunted nose.

Gupta, Roop N.↗
NASA NTRS1989

On hypersonic shock layer and its extension beyond the Navier-Stokes level

An extension of the continuum model beyond the Navier-Stokes (NS) level and related issues on problem formulation are examined for a hypersonic shock layer on the basis of Grad's thirteen-moment equations for a Maxwell gas. The 13-moment system, simplified consistently with a fully viscous version of the thin shock-layer approximation, permits correlation with the corresponding NS-based solution. With the exception of pressure and density, several flow properties including normal stress, shear stress and normal heat flux along a streamline are unaffected by translational nonequilibrium and are therefore predicted correctly by the NS solution to the leading order, even in a domain far from translational equilibrium where molecular-transport processes rank equally with the convection.

Cheng, H. K.↗
NASA NTRS2019

Current Status of Shock Layer Radiation Studies for Planetary Probes

Radiative heating by the shock layer gases surrounding an entry probe is an important heating mechanism for many planetary entries. The magnitude of radiative heating for planetary atmospheres may be characterized with flight similarity in a shock tube capable of obtaining flight relevant velocities and atmospheric density/composition. Over the last decade, studies performed in the Electric Arc Shock Tube (EAST) at NASA Ames have characterized the radiative heating magnitudes for most relevant planetary destinations: Mars, Venus, Titan, Saturn, Uranus. Predictions of heating for a given entry trajectory are simulated by a combination of hypersonic flowfield modeling and the radiation code, NEQAIR, and then compared to the EAST test data. This paper will discuss the measurements, summarize the current simulation capability and provide indications for destination specific radiative heating uncertainties.

Cruden, Brett A.↗
NASA NTRS1989

An approximate viscous shock layer method for calculating the hypersonic flow over blunt-nosed bodies

The approximate axisymmetric method presented for accurately calculating the surface and flowfield properties of fully viscous hypersonic flow over blunt-nosed bodies incorporates the turbulence model of Cebeci-Smith (1970) and the equilibrium air tables of Hansen (1959). The method is faster than the parabolized Navier-Stokes or viscous shock layer solvers that it could replace for preliminary design determinations. Surface heat transfer and pressure predictions for the present method are comparable with the more accurate viscous shock layer method as well as flight test and wind tunnel data. A starting solution is not required.

Grantz, A. C.↗
NASA NTRSDate not supplied

Impact of Trace CH 4 on Shock Layer Radiation in Outer Planet Entry

This paper reports experimental characterization of shock layer radiation from H 2 /He mixtures with a small amount of methane (CH 4 ) addition in the Electric Arc Shock Tube at NASA Ames Research Center. The work follows on a previous test series for entry probes to Saturn and Uranus, which quantified the expected radiance in the absence of methane. However, the Saturn stratosphere is estimated to have approximately 0.4% of CH 4 . The current test series utilized mixtures of 0.886/0.110/0.004 H 2 /He/CH 4 (by mole.) Freestream pressures included 0.1 and 0.5 Torr and velocities from 15-26 km/s. Data compares favorably to similar conditions collected in the Oxford T6 facility. Additional radiation features attributable to CH and C 2 Swan bands are observed, albeit at low intensities. Comparisons to data collected in previous EAST tests suggest that the CH 4 does not significantly alter reaction kinetics below 26 km/s.

Radiation↗
NASA NTRS1992

Numerical simulations of non-equilibrium shock layers with efficient implicit schemes

Current and future calculations of nonequilibrium shock layers require the use of a very large number of equations, due to a multiplicity of chemical species, excited states, and internal energy modes. The computational cost associated with the use of standard implicit methods becomes prohibitive; it is therefore desirable to examine the potential of several methods and determine if any can be projected to be more efficient and accurate for large systems of equations. Here, the performance of several implicit schemes on several simple practical examples of reacting flows is examined. The Euler equations are solved by three different implicit methods, and two methods of coupling between the fluid dynamics and the chemistry are studied. Several cases of stiffness are considered and both 1D and 2D examples are computed.

Cambier, Jean-Luc↗