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NASA NTRS1974

An approximate inviscid radiating flow-field analysis for sphere-cone Venusian entry vehicles

A computational method based on the earlier work of one of the authors has been improved and modified to provide an accurate and rapid prediction of the radiating flow about blunt conical probes entering the atmosphere of Venus. Special features include a more general approximate equation of state, a more rapidly converging iteration scheme, a 38-step absorption coefficient model for a Venus atmosphere gas mixture model, and a shock-shape formula which yields a computed body shape in excellent agreement with the desired body. The method was used to calculate distributions of radiative heating for a large spherically blunted conical probe vehicle (1.219 m base diameter) and for three small spherically blunted conical probe vehicles (0.724 m base diameter). Solutions obtained with the presently developed approximate method required short computing times of the order of 1 to 3 minutes for each complete solution and gave agreements of 10% to 15% with the more exact predictions.

Falanga, R. A.↗

NASA NTRS1988

Shatter cones: Diagnostic impact signatures

Uniquely fractured target rocks known as shatter cones are associated with more than one half the world's 120 or so presently known impact structures. Shatter cones are a form of tensile rock failure in which a positive conical plug separates from a negative outer cup or mold and delicate ornaments radiating from an apex are preserved on surfaces of both portions. Although distinct, shatter cones are sometimes confused with other striated geologic features such as ventifacts, stylolites, cone-in-cone, slickensides, and artificial blast plumes. Complete cones or solitary cones are rare, occurrences are usually as swarms in thoroughly fractured rock. Shatter cones may form in a zone where an expanding shock wave propagating through a target decays to form an elastic wave. Near this transition zone, the expanding primary wave may strike a pebble or other inhomogeneity whose contrasting transmission properties produce a scattered secondary wave. Interference between primary and secondary scattered waves produce conical stress fields with axes perpendicular to the plane of an advancing shock front. This model supports mechanism capable of producing such shatter cone properties as orientation, apical clasts, lithic dependence, and shock pressure zonation. Although formational mechanics are still poorly understood, shatter cones have become the simplest geologic field criterion for recognizing astroblemes (ancient terrestrial impact structures).

Mchone, J. F.↗

NASA NTRS1976

Exit of a blast wave from a conical nozzle

The Eulerian computer code DORF was used in the analysis of a two-dimensional, unsteady flow field resulting from semi-confined explosions for propulsive applications. Initially, the ambient gas inside the conical shaped nozzle is set into motion due to the expansion of the explosion product gas, forming a shock wave. When this shock front exits the nozzle, it takes almost a spherical form while a complex interaction between the nozzle and compression and rarefaction waves takes place behind the shock. The results show an excellent agreement with experimental data.

Kim, K.↗

NASA NTRS1993

Prediction and control of vortex-dominated and vortex-wake flows

This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.

Kandil, Osama↗

NASA NTRS1963

Application of Dorodnitsyn's Integral Method to Nonequilibrium Flows over Pointed Bodies

Dorodnitsyn's integral method is used to obtain an approximate solution to the supersonic nonequilibrium flow over pointed bodies with attached shock waves. The partial differential equations governing the flow are converted to an approximate set of ordinary equations, which are solved by numerical integration starting at the body tip. Detailed analytical and numerical results for the first approximation are presented, considering the vibrational relaxation of a diatomic gas over a wedge or cone. It is shown that the first approximation yields: (1) The exact flow-variable gradients at the wedge tip (2) Expressions for the flow-variable gradients at the cone tip which are in agreement with extrapolations of characteristics calculations (3) A good approximate algebraic solution for frozen or equilibrium conical flow (4) An approximate expression for the nonequilibrium-flow stream function which affords a means of obtaining variations across the shock layer of the temperature and vibrational energy. Numerical results for both the wedge and cone compare favorably with identical cases computed by the method of characteristics.

NONEQUILIBRIUM FLOW↗

NASA NTRS1992

Unsteady separation in sharp fin-induced shock wave/turbulent boundary layer interaction at Mach 5

Fluctuating wall-pressure measurements are made in shock-wave/turbulent-boundary-layer interactions generated by sharp/unswept fins at angles of attack of 16, 18, 20, 22, 24, 26, and 28 degrees at Mach 5. The experiment was conducted under approximately adiabatic wall temperature conditions. The mean and rms pressure distributions can be collapsed in conical coordinates. The wall-pressure signal near separation is intermittent for all angles of attack (16-28 deg) and is qualitatively similar to that measured in unswept flows. However, the shock frequencies are higher - about 5 kHz compared to 0.5-1 kHz. Over the range of sweepbacks examined, from 25-55 deg, the spectral content of the fluctuating pressures does not change. Thus, the increase in separation-shock frequency from 1 to 5 kHz occurs at lower interaction sweepback and is not a continuous process with increasing sweepback. Power spectra at the position of maximum rms in the intermittent region for interactions in different incoming boundary layers have the same center frequency. The maximum rms in the intermittent region correlates with interaction sweepback, not with overall inviscid pressure rise.

Schmisseur, J. D.↗

NASA NTRS1976

Wing shielding of high-velocity jet and shock-associated noise with cold and hot flow jets

Jet exhaust noise shielding data are presented for cold and hot flows (ambient to 1100 K) and pressure ratios from 1.7 to 2.75. A nominal 9.5-cm diameter conical nozzle was used with simple shielding surfaces that were varied in length from 28.8 to 114.3 cm. The nozzle was located 8.8 cm above the surfaces. The acoustic data with the various shielding lengths are compared to each other and to that for the nozzle alone. In general, short shielding surfaces that provided shielding for subsonic jets did not provide as much shielding for jets with shock noise; however, long shielding surfaces did shield shock noise effectively.

Von Glahn, U.↗

NASA NTRS2000

Internal Designs Application for Inlet and Nozzle Aeroperformance Improvement

The following research results are based on development of an approach previously proposed by the authors for optimum nozzle design to obtain maximum thrust. The design was denoted a Telescope nozzle. A Telescope nozzle contains one or several internal designs of certain location, which are inserted at certain locations into a divergent conical or planar main nozzle near its exit. Such a design provides additional thrust augmentation over 20% by comparison with the optimum single nozzle of equivalent lateral area. What is more, recent experimental acoustic tests have discovered an essential noise reduction due to Telescope nozzles application. In this paper, some additional theoretical results are presented for Telescope nozzles and a similar approach is applied for aeroperformance improvement of a supersonic inlet. In addition, a classic gas dynamics problem of a similar supersonic flow into a plate has been analyzed. In some particular cases, new exact analytical solutions are obtained for a flow into a wedge with an oblique shock wave. Numerical simulations were conducted for supersonic flow into a divergent portion of a 2D or axisymmetric nozzle with several plane or conical designs as well as into a 2D or axisymmetric supersonic inlet with a forebody. The 1st order Kryko-Godunov marching numerical scheme for inviscid supersonic flows was used. Several cases were tested using the NASA CFL3d code based on full Navier-Stokes equations. Numerical simulation results have confirmed essential benefits of Telescope design applications in propulsion systems.

Gilinsky, M.↗

NASA NTRS2000

Internal Designs Application for Inlet and Nozzle Aeroperformance Improvement

The following research results are based on development of an approach previously proposed by the authors for optimum nozzle design to obtain maximum thrust. The design was denoted a Telescope nozzle. A Telescope nozzle contains one or several internal designs of certain location, which are inserted at certain locations into a divergent conical or planar main nozzle near its exit. Such a design provides additional thrust augmentation over 20% by comparison with the optimum single nozzle of equivalent lateral area. What is more, recent experimental acoustic tests have discovered an essential noise reduction due to Telescope nozzles application. In this paper, some additional theoretical results are presented for Telescope nozzles and a similar approach is applied for aeroperformance improvement of a supersonic inlet. In addition, a classic gas dynamics problem of a similar supersonic flow into a plate has been analyzed. In some particular cases, new exact analytical solutions are obtained for a flow into a wedge with an oblique shock wave. Numerical simulations were conducted for supersonic flow into a divergent portion of a 2D or axisymmetric nozzle with several plane or conical designs as well as into a 2D or axisymmetric supersonic inlet with a forebody. The 1st order Kryko-Godunov march- ing numerical scheme for inviscid supersonic flows was used. Several cases were tested using the NASA CFL3d code based on full Navier-Stokes equations. Numerical simulation results have confirmed essential benefits of Telescope design applications in propulsion systems.

Gilinsky, M.↗

NASA NTRS1976

Wing shielding of high velocity jet and shock-associated noise with cold and hot flow jets

Jet exhaust noise shielding data are presented for cold and hot flows (ambient to 1,100 K) and pressure ratios from 1.7 to 2.75. A nominal 9.5-cm diameter conical nozzle was used with simple shielding surfaces that were varied in length from 28.8 to 114.3 cm. The nozzle was located 8.8 cm above the surfaces. The acoustic data with the various sheilding lengths are compared to each other and to that for the nozzle alone. In general, short shielding surfaces that provided shielding for subsonic jets did not provide as much shielding for jets with shock noise, however, long shielding surfaces did shield shock noise effectively.

Vonglahn, U.↗

NASA NTRS1980

A unique coannular plug nozzle jet noise prediction procedure

The work presents a method for predicting jet mixing and shock noise spectra from coannular plug nozzles operated in the inverted velocity profile mode. It is shown that the jet mixing noise prediction method is based on the physics of the flow and its noise radiating characteristics, modeling the source spectrum, eddy convection, and fluid shrouding in a simplistic fashion. Further, the shock noise prediction procedure is described, noting that it is an extension of the Fisher-Harper-Bourne method for conical nozzles. Finally, it is concluded that the method has the potential of being extended to suppressors of complex geometries.

Bhutiani, P. K.↗

NASA NTRS1986

Plasma processes driven by current sheets and their relevance to the auroral plasma

Plasma processes dealing with ac and dc electric fields, the formation of ion beams and conics, and electron acceleration are considered, and similarities between simulation results and satellite-based observations are discussed. Electrostatic shock-type electric fields are found to occur near the current sheet edges, and double layers having upward electric fields form inside the sheet and are distinguishable from the large perpendicular electric fields only in wide sheets with thicknesses much greater than the ion Larmor radius. It is found that the most energetic ions have pitch angles near 90 deg, indicating a large perpendicular acceleration of the ions, and that the downward accelerating electrons inside the sheet are neither monoenergetic nor perfectly field aligned.

Singh, Nagendra↗

NASA NTRS2012

Lunar Precursor Effects in the Solar Wind and Terrestrial Magnetosphere

The two ARTEMIS probes observe significant precursor activity upstream from the Moon, when magnetically connected to the dayside lunar surface. The most common signature consists of high levels of whistler wave activity near half of the electron cyclotron frequency. This precursor activity extends to distances of many thousands of km, in both the solar wind and terrestrial magnetosphere. In the magnetosphere, electrons reflect from a combination of magnetic and electrostatic fields above the lunar surface, forming loss cone distributions. In the solar wind they generally form conics, as a result of reflection from an obstacle moving with respect to the plasma frame (just as at a shock). The anisotropy associated with these reflected electrons provides the free energy source for the whistlers, with cyclotron resonance conditions met between the reflected source population and Moonward-propagating waves. These waves can in turn affect incoming plasma, and we observe significant perpendicular electron heating and plasma density depletions in some cases. In the magnetosphere, we also observe broadband electrostatic modes driven by beams of secondary electrons and/or photoelectrons accelerated outward from the surface. We also occasionally see waves near the ion cyclotron frequency in the magnetosphere. These lower frequency waves, which may result from the presence of ions of lunar origin, modulate the whistlers described above, as well as the electrons. Taken together, our observations suggest that the presence of the Moon leads to the formation of an upstream region analogous in many ways to the terrestrial electron foreshock.

Magnetosphere↗

NASA NTRS1977

Supersonic flow about circular cones at large angles of attack - A floating discontinuity approach

The technique of floating shock fitting is adapted to the computation of the inviscid flowfield about circular cones in a supersonic free stream at angles of attack that exceed the cone half-angle. In those regions in which the governing conical equations are mixed elliptic-hyperbolic, the fully hyperbolic form is obtained by the addition of the temporal derivative. The resulting equations are applicable over the complete range of free-stream Mach numbers, angles of attack and cone half-angles for which the bow shock is attached. An explicit finite-difference algorithm is used to obtain the solution by an unsteady relaxation approach. The bow shock, embedded crossflow shock, and vortical singularity in the leeward symmetry plane are all treated as floating discontinuities in a fixed computational mesh. The method yields excellent results for the bow and embedded shocks, however, the solution in the leeward symmetry plane exhibits viscous-like effects and does not appear to adequately predict the behavior of the vortical singularity.

Daywitt, J.↗

NASA NTRS1985

Computation of three-dimensional shock-wave/turbulent boundary-layer interaction flows

Solutions of the Reynolds-averaged Navier-Stokes equations, employing a two-equation turbulence model, are presented and compared with measurements from a series of supersonic shock-wave/boundary-layer interaction experiments. The test flows include swept-compression corners and axisymmetric bodies with either skewed or segmented conical flares. The solutions correctly predict all major qualitative features of the flow field. However, for flow fields with large separated zones, significant quantitative differences are observed between the computed and experimental results. Possible reasons for these differences are discussed.

Horstman, C. C.↗

NASA NTRS1988

Particle acceleration and wave emissions associated with the formation of auroral cavities and enhancements

A unified model is presented which interrelates the various processes involved in auroral particle acceleration and the associated wave emissions, and it is shown how energy is coupled from the magnetosphere into the ionosphere. The phenomena in the magnetotail which can provide the source of free energy for the perpendicular electrostatic shocks are identified along with the associated potential structures in the nightside auroral region. The characteristics of the particle acceleration produced by the shock are described, including efficiency and energy transport between magnetospheric and ionospheric plasmas, the properties of the particle distributions throughout the shock region and return current regions, and the associated wave emissions. The source of free energy for the generation of ion conics is identified, as are the signatures for the formation of plasma cavities and/or enhancements.

Winglee, R. M.↗

NASA NTRS1987

An aerothermodynamic study of slender conical vehicles

A numerical study was performed to assess the applicability of some current techniques which can be used for aerothermal predictions over slender spherically blunted cones. Predictions using a viscous-shock-layer method and several engineering approaches were compared with experimental results from flight and ground-based tests, with each other, and with other detailed results. Good agreement was obtained in comparisons with laminar and turbulent heating data from the Reentry F flight vehicle and with the wind-tunnel data. In particular, the viscous-shock-layer method was shown to yield excellent comparisons and should be useful in providing detailed flowfield and surface values for slender blunted cones. Additional predictions were obtained with these methods for two 5-deg half-angle cones with different nose radii to illustrate the effects of nose bluntness and angle of attack on drag and heat transfer. These results demonstrate the benefit of nose blunting with respect to heating and drag for laminar and transitional flow at zero-lift conditions and the benefit of heating reduction at angle of attack. Detailed comparison of the engineering code predictions with the viscous-shock-layer results for these additional cases generally showed good agreement except for the laminar prodictions at angle of attack on the forward cone surface. Nonequilibrium calculations at 0-deg angle of attack showed that substantial benefits of low surface catalysis existed only in the nose-dominated region.

Thompson, R. A.↗

NASA NTRS1988

Solutions for hypersonic viscous flow over delta wings

A conical Navier-Stokes solver is developed to study hypersonic flow over delta wings. The differencing scheme used is van Leer flux vector splitting with MUSCL differencing. A flux limiter which involves a second difference in pressure was found to provide sharp, nonoscillatory shocks in windward and leeward flow regions. The governing equations are cast in finite-volume form and are solved using an explicit multistage method. A von Neumann stability analysis of a one-dimensional flux split model is used to predict the stability characteristics of the conical solver. The stability behavior of the scheme is found to strongly depend on the stage coefficients of the multistage scheme and on the order of accuracy of the upwind discretization.

Ruffin, Stephen M.↗