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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Interactions between Coronal Mass Ejections Viewed in Coordinated Imaging and In Situ Observations

The successive coronal mass ejections (CMEs) from 2010 July 30 - August 1 present us the first opportunity to study CME-CME interactions with unprecedented heliospheric imaging and in situ observations from multiple vantage points. We describe two cases of CME interactions: merging of two CMEs launched close in time and overtaking of a preceding CME by a shock wave. The first two CMEs on August 1 interact close to the Sun and form a merged front, which then overtakes the July 30 CME near 1 AU, as revealed by wide-angle imaging observations. Connections between imaging observations and in situ signatures at 1 AU suggest that the merged front is a shock wave, followed by two ejecta observed at Wind which seem to have already merged. In situ measurements show that the CME from July 30 is being overtaken by the shock at 1 AU and is significantly compressed, accelerated and heated. The interaction between the preceding ejecta and shock also results in variations in the shock strength and structure on a global scale, as shown by widely separated in situ measurements from Wind and STEREO B. These results indicate important implications of CME-CME interactions for shock propagation, particle acceleration and space weather forecasting.

Liu, Ying D.↗
NASA NTRS1979

Computations of unsteady transonic flow governed by the conservative full potential equation using an alternating direction implicit algorithm

A development was the time linearization of the density function. This linearization reduces the solution process from solving just a single equation. Two sample cases were computed. First, a one dimensional traveling shock wave was computed and compared with the analytic solution. Second, a two dimensional case was calculated for a flow field which resulted from a thickening and subsequently, thinning airfoil. The resulting flow field, which included a traveling shock wave, was compared to the flow field obtained from the low frequency, small disturbance, transonic equation.

Goorjian, P. M.↗
DOE OSTI2021

The LISE package: solvers for static and time-dependent superfluid local density approximation equations in three dimensions

Nuclear implementation of the density functional theory (DFT) is at present the only microscopic framework applicable to the whole nuclear landscape. The extension of DFT to superfluid systems in the spirit of the Kohn-Sham approach, the superfluid local density approximation (SLDA) and its extension to time-dependent situations, time-dependent superfluid local density ap- proximation (TDSLDA), have been extensively used to describe various static and dynamical problems in nuclear physics, neutron star crust, and cold atom systems. In this paper, we present the codes that solve the static and time-dependent SLDA equations in three-dimensional coordinate space without any symmetry restriction. These codes are fully parallelized with the message passing interface (MPI) library and take advantage of graphic processing units (GPU) for accelerating execution. The dynamic codes have checkpoint/restart capabilities and for initial conditions one can use any generalized Slater determinant type of wave function. The code can describe a large number of physical problems: nuclear fission, collisions of heavy ions, the interaction of quantized vor- tices with nuclei in the nuclear star crust, excitation of superfluid fermion systems by time dependent external fields, quantum shock waves, domain wall generation and propagation, the dynamics of the Anderson-Bogoliubov-Higgs mode, dynamics of fragmented condensates, vortex rings dynamics, generation and dynamics of quantized vortices, their crossing and recombinations and the incipient phases of quantum turbulence.

Jin, Shi↗
NASA NTRS1980

Implicit computations of unsteady transonic flow governed by the full-potential equation in conservation form

An alternating-direction implicit algorithm is presented for solving the conservative, full-potential equation for unsteady, transonic flow. A new development is the time-linearization of the density function. This linearization reduces the solution process from one of solving a system of two equations at each mesh point to one of solving a single equation. Two sample cases are computed. First, a one-dimensional traveling shock wave is computed and compared with the analytic solution. Second, a two-dimensional case is computed of a flow field that results from a thickening and subsequently thinning airfoil. The resulting flow field, which includes a traveling shock wave, is compared to the flow field obtained from the low-frequency, small-disturbance, transonic equation.

Goorjian, P. M.↗
NASA NTRS1969

Aerodynamic Characteristics of an 11-Percent-Thick Symmetrical Supercritical Airfoil at Mach Numbers Between 0.30 and 0.85

The aerodynamic characteristics of an 11 percent thick symmetrical supercritical airfoil were determined in an 8 foot transonic pressure tunnel over a Mach number range of 0.30 to 0.85. The Reynolds number of the tests, based on the airfoil chord, varied with Mach number over a range of 360 million to 774 million. The geometric angle of attack varied from -0.5 to 10.5 deg. The abrupt drag rise for the supercritical airfoil at zero normal force conditions occurs at a Mach number just above 0.82. The corresponding drag rise Mach number for a conventional NACA 0012 airfoil is approximately 0.70. At zero normal force conditions, the level of supervelocity over the supercritical airfoil is considerably reduced from that for the NACA 0012 airfoil. Also, the shock wave for the supercritical airfoil is substantially weaker than that for the NACA 0012 airfoil. For a Mach number of 0.82 and zero normal force, the flow over the present airfoil is supercritical; however, there is no discernible shock wave in the flow, indicating near isentropic recompression.

Blackwell, J. A., Jr.↗
NASA NTRS1992

Time dependent heat transfer rates in high Reynolds number hypersonic flowfields

Time dependent heat transfer rates have been calculated from time dependent temperature measurements in the vicinity of shock-wave boundary-layer interactions due to conical compression ramps on an axisymmetric body. The basic model is a cylindrical body with a 10 degree conical nose. Four conical ramps, 20, 25, 30, and 35 degrees serve as shock wave generators. Flowfield surveys have been made in the vicinity of the conical ramp vertex, the separation point, and the reattachment point. A significant effort was made to characterize the natural frequencies and relative powers of the resulting fluctuations in heat transfer rates. This research effort, sponsored jointly by NASA and the Air Force, was conducted in the Air Force Flight Dynamics Directorate High Reynolds Facility. The nominal freestream Mach number was 6, and the freestream Reynolds numbers ranged from 2.2 million/ft to 30.0 million/ft. Experimental results quantify temperature response and the resulting heat transfer rates as a function of ramp angle and Reynolds number. The temperature response within the flowfield appears to be steady-state for all compression ramp angles and all Reynolds numbers, and hence, the heat transfer rates appear to be steady-state.

Flanagan, Michael J.↗
NASA NTRS1973

A composite model for a class of electric-discharge shock tubes

A gasdynamic model is presented and analyzed for a class of shock tubes that utilize both Joule heating and electromagnetic forces to produce high-speed shock waves. The model consists of several stages of acceleration in which acceleration to sonic conditions is achieved principally through heating, and further acceleration of the supersonic flow is obtained principally through use of electromagnetic forces. The utility of the model results from the fact that it predicts a quasi-steady flow process, mathematical analysis is straightforward, and it is even possible to remove one or more component stages and still have the model related to a possible shock-tube flow. Initial experiments have been performed where the electrical discharge configuration and current level were such that Joule heating was the dominant form of energy addition present. These experiments indicate that the predictions of the model dealing with heat addition correspond quite closely to reality. The experimental data together with the theory show that heat addition to the flowing driver gas after diaphragm rupture (approach used in the model) is much more effective in producing high-speed shock waves than heating the gas in the driver before diaphragm rupture, as in the case of the arc-driven shock tube.

Elkins, R. T.↗
DOE OSTI2024

The Computational Analysis of a Generic Hypersonic Store Separation

Many current hypersonic vehicles involve a main vehicle from which components separate during flight and presents simulation challenges such as shock-shock interactions, highly nonlinear interactions, and shock wave boundary layer interactions. These aerodynamic phenomena influence the attitude and trajectory of each object, which needs to be understood before large-scale experiments can be run. To gain a generic understanding of the process, high-fidelity Reynolds-averaged Navier-Stokes solutions are performed on a conical vehicle geometry passing through an oblique shock wave that is representative of different configurations and scenarios. Trajectory and applied forces are tracked and show the vehicle’s dynamics are predominantly the result of differential flow incidence angles causing a strong shock; this leads to a large pressure increase over a fraction of the vehicle, which influences pitch. The vehicle appears to follow conventional stability theory with detached eddy simulation and small disturbances in initial attitude shown to have minimal influence on the scenario.

Savery, Ryan↗
NASA NTRS1983

Finite difference solutions to shocked acoustic waves

The MacCormack, Lambda and split flux finite differencing schemes are used to solve a one dimensional acoustics problem. Two duct configurations were considered, a uniform duct and a converging-diverging nozzle. Asymptotic solutions for these two ducts are compared with the numerical solutions. When the acoustic amplitude and frequency are sufficiently high the acoustic signal shocks. This condition leads to a deterioration of the numerical solutions since viscous terms may be required if the shock is to be resolved. A continuous uniform duct solution is considered to demonstrate how the viscous terms modify the solution. These results are then compared with a shocked solution with and without viscous terms. Generally it is found that the most accurate solutions are those obtained using the minimum possible viscosity coefficients. All of the schemes considered give results accurate enough for acoustic power calculations with no one scheme performing significantly better than the others.

Walkington, N. J.↗
DOE OSTI2022

Planar, longitudinal, compressive waves in solids: Thermodynamics and uniaxial strain restrictions

A new tri-axial pressure-based constitutive expression has been found using Cauchy's stress tensor. This stress state emphasizes pressure and shear stress. The description is a pressure plus an effective shear stress allowing for a constitutive law based on atomic solid-state phase changes in crystalline cells due to pressure plus shear-based dislocation motion commonly associated with plasticity. Pressure has a new role in the material's constitutive response as it is separated from plasticity. The thermo-mechanical system describes third-order Gibbs’ expressions without specific volume restrictions placed upon the material. Isothermally, the ratio of heat to shear work in elastic copper is shown to approach zero at a very low temperature and become larger than one as temperature approaches melting. Wave compression models investigated are elastic and plastic: in fully elastic materials, the planar wave is restricted by Poisson's effect although plastic shear changes this constraint. Plastic deformation, dominated by dissipative shear stresses in uniaxial strain, heats the material while excluding phase changes from hydrostatic pressures. The material properties per se across Hugoniot shocks are described with entropy concepts. Shock waves are exceedingly complex since the constitutive laws are linked at extreme temperatures, pressures, and shear stresses. Isothermal, isentropic, isochoric, and iso-shear conditions are used throughout with Jacobian algebra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1974

Recent theories of cavitation damage including non-symmetrical bubble collapse effects

Theories of cavitation damage mechanisms are discussed. Photographic evidence has shown that the actual collapse of bubbles near a symmetry-destroying feature such as a nearby wall results in a toroidal-like collapse, with the final generation of a liquid microjet oriented toward the wall. Numerical analyses indicate that the shock wave intensity emitted during collapse is not likely to be strong enough to be damaging to most materials. It has been determined that actual damage is usually a result of a combination of impact effect of the microjet and the shock wave pressures generated by bubble rebounds.

Hammitt, F. G.↗
NASA NTRS1993

Chondrule formation by clumpy accretion onto the solar nebula

Chondrule textures and compositions appear to require rapid heating of precursor grain aggregates to temperatures in the range 1500 K to 2100 K, cooling times on the order of hours, and episodic and variable intensity events in order to produce chondrule rims and chemically distinct groups. Nebula shock waves have been proposed by Hood and Horanyi as a physical mechanism that may be capable of meeting the meteoritical constraints. Motivated by astronomical observations of the close environments of young stars, we suggest that the source of the nebula shock waves may be clumpy accretion onto the solar nebula - that is, episodic impacts onto the nebula by discrete cloud clumps with masses of at least 10(exp 22) g. If the cloud clumps are massive enough (10(exp 26) g), the resulting shockwave may be able to propagate to the midplane and process precursor aggregates residing in a dust sub-disk.

Boss, A. P.↗
NASA NTRS1976

Numerical analysis of a two-dimensional nonsteady detonations

In the present work a system of two-dimensional nonsteady hydrodynamic and chemical kinetic equations was numerically integrated for an exothermic system. Assumed two-step reaction model simulates practically an oxyhydrogen mixture. The calculation starts from a plane Chapman-Jouguet detonation as an initial condition. Two-dimensional disturbances are generated by artificially placing nonuniformities ahead of the detonation front. Regardless of the difference of the given initial disturbances, a fixed number of triple shock waves were produced for a fixed combination of mixture model and geometry when the transition period was over. This shows that for a given detonation tube geometry any exothermic system has its own characteristic multidimensional structure. The obtained number of triple shock waves contained in the detonation front was in agreement with existing experimental observations under the same condition.

Taki, S.↗
NASA NTRS1978

A technique for scale model rocket base heating tests in a very large vacuum chamber

A series of tests was performed with a 0.040 scale Shuttle Orbiter Base Heating Model in a large vacuum chamber to determine the thermal effects of engine plume recirculation and direct engine plume impingement. The oxygen- and hydrogen-fueled model was fired through a range of simulated altitudes and configurations with varied engine gimbal angles and 'engine-out' combinations. Some of the special problems associated with conducting tests of this type related primarily to obtaining valid temperature and pressure data in the extremely short run times available. Run time is limited by the reflection of shock waves from the chamber wall, propellant charge-tube wave times, the time required to reach steady-state conditions for the engines, and model heating limitations. The 'data window' for potentially valid data usually begins with stabilized engine conditions and terminates with pressure perturbations from either of the aforementioned shock waves. The general approach for coping with these limitations and the method used to obtain valid data during the short data window (of the order of thirty milliseconds) are discussed.

Williams, F. U.↗
NASA NTRS1987

An adaptive grid, unsteady model for two-dimensional magnetohydrodynamic (MHD) flow

An adaptive grid finite difference method for solving multi-dimensional, time-dependent, magnetohydrodynamic (MHD) equations is developed. The method is capable of solving problems that include high gradients due to geometry, propagation of shock waves and unsteady boundary conditions. The grid generation technique is based on variational principles with direct control over grid concentration, smoothness and skewness. An example for a two-dimensional MHD simulation of the propagation of a solar-flare-generated shock wave in solar wind flow in the heliographic equatorial plane is selected for illustration of this method.

Panitchob, Supat↗
NASA NTRS1978

Feasibility of wing shielding of the airplane interior from the shock noise generated by supersonic tip speed propellers

A high tip speed turboprop is being considered as a future energy conservative airplane. The high tip speed of the propeller, combined with the speed of the airplane, results in supersonic relative flow on the propeller tips. These supersonic blade sections could generate noise that is a cabin environment problem. The feasibility of using wing shielding to lessen the impact of this supersonic propeller noise was investigated. An analytical model is chosen which considers that shock waves are associated with the propeller tip flow and indicates how they would be prevented from impinging on the airplane fuselage. An example calculation is performed where a swept wing is used to shield the fuselage from significant portions of the propeller shock waves.

Dittmar, J. H.↗
NASA NTRS2011

Turbulence Modeling for Shock Wave/Turbulent Boundary Layer Interactions

Accurate aerodynamic computational predictions are essential for the safety of space vehicles, but these computations are of limited accuracy when large pressure gradients are present in the flow. The goal of the current project is to improve the state of compressible turbulence modeling for high speed flows with shock wave / turbulent boundary layer interactions (SWTBLI). Emphasis will be placed on models that can accurately predict the separated region caused by the SWTBLI. These flows are classified as nonequilibrium boundary layers because of the very large and variable adverse pressure gradients caused by the shock waves. The lag model was designed to model these nonequilibrium flows by incorporating history effects. Standard one- and two-equation models (Spalart Allmaras and SST) and the lag model will be run and compared to a new lag model. This new model, the Reynolds stress tensor lag model (lagRST), will be assessed against multiple wind tunnel tests and correlations. The basis of the lag and lagRST models are to preserve the accuracy of the standard turbulence models in equilibrium turbulence, when the Reynolds stresses are linearly related to the mean strain rates, but create a lag between mean strain rate effects and turbulence when nonequilibrium effects become important, such as in large pressure gradients. The affect this lag has on the results for SWBLI and massively separated flows will be determined. These computations will be done with a modified version of the OVERFLOW code. This code solves the RANS equations on overset grids. It was used for this study for its ability to input very complex geometries into the flow solver, such as the Space Shuttle in the full stack configuration. The model was successfully implemented within two versions of the OVERFLOW code. Results show a substantial improvement over the baseline models for transonic separated flows. The results are mixed for the SWBLI assessed. Separation predictions are not as good as the baseline models, but the over prediction of the peak heat flux downstream of the reattachment shock that plagues many models is reduced.

Lillard, Randolph P.↗
NASA NTRS1973

Composition of the earth's atmosphere by shock-layer radiometry during the PAET entry probe experiment.

A determination of the composition of the earth's atmosphere obtained from onboard radiometer measurements of the spectra emitted from the bow shock layer of a high-speed entry probe is reported. The N2, O2, CO2, and noble gas concentrations in the earth's atmosphere were determined to good accuracy by this technique. The results demonstrate unequivocally the feasibility of determining the composition of an unknown planetary atmosphere by means of a multichannel radiometer viewing optical emission from the heated atmospheric gases in the region between the bow shock wave and the vehicle surface. The spectral locations in this experiment were preselected to enable the observation of CN violet, N2(+) first negative and atomic oxygen emission at 3870, 3910, and 7775 A, respectively. The atmospheric gases were heated and compressed by the shock wave to a peak temperature of about 6100 K and a corresponding pressure of 0.4 atm. Complete descriptions of the data analysis technique and the onboard radiometer and its calibration are given.

Whiting, E. E.↗