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NASA NTRS1988

Conduction-driven chromospheric evaporation in a solar flare

Observations of gentle chromospheric evaporation during the cooling phase of a solar flare are presented. Line profiles of the low-temperature (T of about 6 x 10 to the 6th K) coronal Mg XI line, observed with the X-Ray Polychromator on the Solar Maximum Mission, show a blueshift that persisted for several minutes after the impulsive heating phase. This result represents the first detection of an evaporation signature in a soft X-ray line formed at this low temperature. By combining the Mg XI blueshift velocity data with simultaneous measurements of the flare temperature derived from Ca XIX observations, it is demonstrated that the upward flux of enthalpy transported by this gently evaporating plasma varies linearly with the downward flux of thermal energy conducted from the corona. This relationship is consistent with models of solar flares in which thermal conduction drives chromospheric evaporation during the early part of the cooling phase.

Zarro, Dominic M.↗

NASA NTRS1988

Development and experimental test of an analytical model of the orifice pulse tube refrigerator

An analytical model for the orifice pulse tube is developed, in which the system is described in terms of average enthalpy flow with such simplifying assumptions as an ideal gas and sinusoidal pressure variation. Phasor analysis is used to represent temperature, pressure, and mass-flow rate waves in vector form. The model predictions, namely, that the refrigeration power of a pulse-tube refrigerator is proportional to the average pressure, the pulse frequency, the mass-flow ratio, and the square of the dynamic pressure ratio, were verified by experimental measurements. It was found that, as a result of the simplifying assumptions, the magnitudes of the refrigeration power predicted by the model were between three and five times greater than experimental values.

Storch, Peter J.↗

NASA NTRS1989

Laser Rayleigh-Scattering During Space Shuttle Entry

Report presents detailed study of capabilities and requirements for equipment of proposed ultraviolet Rayleigh-scattering instrument to be carried aboard Space Shuttle. Density of atmosphere around flightpath measured. With accuracy and resolution, measurements adequate for detection of small-scale meteorological structure affecting analysis of flight dynamic data of reentering spacecraft. Also discusses extensions of concept to measurements of location of, and density as function of position in, shock wave of Space Shuttle. Measurements provide baseline data for verification of computer models of high-enthalpy hypersonic, nonequilibrium, and viscous conditions.

Mckenzie, Robert L.↗

NASA NTRS1989

Algorithm For Hypersonic Flow In Chemical Equilibrium

Implicit, finite-difference, shock-capturing algorithm calculates inviscid, hypersonic flows in chemical equilibrium. Implicit formulation chosen because overcomes limitation on mathematical stability encountered in explicit formulations. For dynamical portion of problem, Euler equations written in conservation-law form in Cartesian coordinate system for two-dimensional or axisymmetric flow. For chemical portion of problem, equilibrium state of gas at each point in computational grid determined by minimizing local Gibbs free energy, subject to local conservation of molecules, atoms, ions, and total enthalpy. Major advantage: resulting algorithm naturally stable and captures strong shocks without help of artificial-dissipation terms to damp out spurious numerical oscillations.

Palmer, Grant↗

NASA NTRS1988

A high heat flux experiment for verification of thermostructural analysis

A major concern in advancing the state of the art technologies for hypersonic vehicles is the development of an aeropropulsion system capable of handling the high heat fluxes during flight. The leading edges of such systems must not only tolerate the maximum heating rates, but must also minimize distortions to the flow field due to excessive blunting and/or thermal warping of the compression surface to achieve the high inlet performance required. A combined analytical and experimental effort to study the aerothermodynamic loads on actively cooled structures for hypersonic applications was established. A hydrogen/oxygen rocket engine was modified to establish a high enthalpy high heat flux environment. The facility provides heat flux levels from about 200 up to 10000 Btu/sq ft/sec. Cross flow and parallel flow regeneratively cooled model can be tested and analyzed by using cooling fluids of water and hydrogen. Results are presented of the experiment and the characteristics of the Hot Gas Test Facility. The predicted temperature results of the cross flow model are compared with the experimental data on the first monolithic specimens and are found to be in good agreement. Thermal stress analysis results are also presented.

Gladden, Herbert J.↗

NASA NTRS1988

A comparison of numerical methods for the prediction of two-dimensional heat transfer in an electrothermal deicer pad

Transient, numerical simulations of the deicing of composite aircraft components by electrothermal heating have been performed in a 2-D rectangular geometry. Seven numerical schemes and four solution methods were used to find the most efficient numerical procedure for this problem. The phase change in the ice was simulated using the Enthalpy method along with the Method for Assumed States. Numerical solutions illustrating deicer performance for various conditions are presented. Comparisons are made with previous numerical models and with experimental data. The simulation can also be used to solve a variety of other heat conduction problems involving composite bodies.

Deicer↗

NASA NTRS1988

A numerical simulation of the full two-dimensional electrothermal de-icer pad

The ability to predict the time-temperature history of electrothermal de-icer pads is important in the subsequent design of improved and more efficient versions. These de-icer pads are installed near the surface of aircraft components, for the specific purpose of removing accreted ice. The proposed numerical model can incorporate the full 2-D geometry through a section of a region (i.e., section of an airfoil), that current 1-D numerical codes are unable to do. Thus, the effects of irregular layers, curvature, etc., can now be accounted for in the thermal transients. Each layer in the actual geometry is mapped via a body-fitted coordinate transformation into uniform, rectangular computational grids. The relevant heat transfer equations are transformed and discretized. To model the phase change that might occur in any accreted ice, in an enthalpy formulation the phase change equations are likewise transformed and discretized. The code developed was tested against numerous classical numerical solutions, as well as against experimental de-icing data on a UH1H rotor blade obtained from the NASA Lewis Research Center. The excellent comparisons obtained show that this code can be a useful tool in predicting the performance of current de-icer models, as well as in the designing of future models.

Masiulaniec, Konstanty C.↗

NASA NTRS1989

Contamination of liquid oxygen by pressurized gaseous nitrogen

The penetration of pressurized gaseous nitrogen (GN2) into liquid oxygen (LOX) was investigated experimentally in the 7-inch High Temperature Tunnel, the pilot tunnel for the 8-foot High Temperature Tunnel (8'HTT) at Langley Research Center. A preliminary test using a nuclear monitor revealed the extent of the liquid nitrogen (LN2) build-up at the LOX interface as a function of GN2 pressure. Then an adaptation of the differential flash vaporization technique was used to determine the binary diffusivity of the LOX-LN2 system at a temperature of 90.2 K. The measured value D equals 0.000086 sq cm/s + or - 25 percent together with two prior measurements at lower temperatures revealed an excellent fit to the Arrhenius equation, yielding a pre-exponential factor D sub 0 equals 0.0452 sq cm/s and an activation enthalpy H equals 1.08 kcal/mol. At a pressure of 1700 psi and holding time of 15 min, the penetration of LN2 into LOX (to a 1 percent contamination level) was found to be 0.9 cm, indicating but minimal impact upon 8'HTT operations.

Zuckerwar, Allan J.↗

NASA NTRS1988

High speed inlet calculations with real gas effects

A 2-D steady-state Navier-Stokes solver has been upgraded to include the effects of frozen and equilibrium air chemistry for applications to high speed flight vehicles. To provide a computationally economical first order approximation to the high temperature physics, variable thermodynamic data is used for the chemically frozen mode to allow for a variation with temperature of the air specific heats and enthalpy. For calculations involving air in chemical equilibrium, a specially modified version of the NASA Lewis Chemical Equilibrium Code, CEC, is used to compute the chemical composition and resultant thermochemical properties. The upgraded solver is demonstrated by comparing results from calorically perfect (C sub p=constant), thermally perfect (frozen) and equilibrium air calculations for a variety of geometries, and flight Mach numbers.

Coirier, William J.↗

NASA NTRS1988

Electron heating and the potential jump across fast mode shocks

Two different methods were applied to determine the cross-shock potential jump in the de Hoffmann-Teller reference frame, using a data set that represented 66 crossings of the terrestrial bow shock and 14 interplanetary shocks observed by various ISEE spacecraft, and one crossing each of the Jovian bow shock and the Uranian bow shock made by the Voyager spacecraft. Results for estimates of the electrostatic potential based on an estimate of the jump in electron enthalpy correlated well with estimates based on Liouville's theorem, although the Liouville-determined values were systematically the higher of the two, suggesting that significant irreversible processes contribute to the shape of the downstream distribution. The potential jump corresponds to approximately 12-15 percent of the incident ion ram kinetic energy, and was found not to be controlled by the Mach number, plasma beta, shock geometry, or electron to ion temperature ratios.

Schwartz, Steven J.↗

NASA NTRS1988

Dendritic solidification in binary alloys

Alloys generally solidify dendritically, and associated with that is the microsegregation of impurities. Pure metals also solidify in dendritic form as 'thermal' dendrites, which actually segregate the system's enthalpy. In this investigation, small additions of solute to succinonitrile have been studied and dendritic growth observed in a supercooled melt. This free dendritic growth-mode is similar to that experienced by equiaxed dendrites found in alloy castings. Observations of these free dendrites include measurement of velocity and tip radius of the dendrites at different supercoolings and solute concentrations.

Chopra, M. A.↗

NASA NTRS1989

Turbulent compressible convection in a deep atmosphere. IV - Results of three-dimensional computations

The behavior of turbulent convection in deep atmospheres is studied by numerically solving the three-dimensional Navier Stokes equations. It is found that the mean vertical velocity is an important link between the buoyancy work and the heat flux. In regions with efficient convection, the total flux is composed of the enthalpy flux and the flux of kinetic energy. The characteristics of these components of the total flux are examined. It is shown that the production of kinetic energy depends on the local variables and the flux. However, the dissipation of kinetic energy is nonlocal. A substantial amount of kinetic energy is carried away from the location of production to be dissipated in lower regions.

Chan, Kwing L.↗

NASA NTRS1989

Calculation of convective heat transfer on highly blunt bodies at flow incidence

An implicit finite-difference code is used to study three-dimensional viscous heat-conducting flows over the forebody of hypersonic vehicles. In the method, adaptive grids are generated to the shock and body contour, and local flow gradients and total enthalpy are used to control numerical dissipation. Typical axisymmetric configurations of a sphere, ellipsoid, and flat-face disk are considered, along with the cases of a blunt 70-deg cone at 0 and 20 deg flow incidences and an asymmetric 60-deg cone raked off at a 73-deg angle.

Li, C. P.↗

NASA NTRS1989

Calculations of rotational flows using stream function

The stream function equation is solved for steady two-dimensional (and axisymmetric) rotational flows. Both finite differences and finite volumes discretization techniques are studied, using generalized body fitted coordinates and unstructured staggered grids, respectively. For inviscid transonic flows, a new artificial viscosity scheme which does not produce any artificial vorticity is introduced, for the stability of the mixed flow calculations and for capturing shocks. The solution of Euler equations, in primitive variables, are also considered. The effects of the artificial viscosity and numerical boundary conditions on the total enthalpy and the vorticity distributions are demonstrated.

Hafez, M.↗

NASA NTRS1989

A finite element solution algorithm for nonlinear thermal problems with severe gradients

An implicit enthalpy - flux component finite element algorithm is presented for nonlinear thermal problems with severe gradients. The algorithm is formulated to permit efficient solution of nonlinear heat transfer problems for unstructured meshes with a large range of element sizes. Two transient conduction examples illustrate the effectiveness of the approach for problems with high temperatures and steep gradients.

Thornton, Earl A.↗

NASA NTRS1988

A high heat flux experiment for verification of thermostructural analysis

A major concern in advancing the state of the art technologies for hypersonic vehicles is the development of an aeropropulsion system capable of handling the high heat fluxes during flight. The leading edges of such systems must not only tolerate the maximum heating rates, but must also minimize distortions to the flow field due to excessive blunting and/or thermal warping of the conmpression surface to achieve the high inlet performance required. A combined analytical and experimental effort to study the aerothermodynamic loads on actively cooled structures for hypersonic applications was established. A hydrogen/oxygen rocket engine was modified to establish a high enthalpy high heat flux environment. The facility provides heat flux levels from about 200 up to 10000 Btu/sq ft/sec. Cross flow and parallel flow regeneratively cooled model can be tested and analyzed by using cooling fluids of water and hydrogen. Results are presented of the experiment and the characteristics of the Hot Gas Test Facility. The predicted temperature results of the cross flow model are compared with the experimental data on the first monolithic specimens and are found to be in good agreement. Thermal stress analysis results are also presented.

Gladden, H. J.↗

NASA NTRS1989

Nonequilibrium shock layer temperature profiles from arc jet radiation measurements

Shock layer temperature profiles are obtained through analysis of radiation from shock layers produced by a blunt body inserted in arc jet flow. Spectral measurements have been made in a nitrogen flow of 54.4 gm/s at an enthalpy of 8.72 MJ/kg. Vibrational temperatures for N2+ are obtained by matching spectral regions from arc jet spectra with spectra generated using the NEQAIR code. Temperature profiles obtained from the radiation layers show a vibrational temperature higher than the rotational temperature near the front of the shock and both temperatures decrease as the flow approaches the body. The spectral measurements are made and analysis completed for four distances, from the surface of the blunt body. The corresponding shock layer thickness is approximately 3.6 cm. Although the shock layer appears to be in thermal nonequilibrium, the measured rotational temperature approaches the single temperature results of viscous shock layer calculations at this test condition.

Blackwell, Harvel E.↗

NASA NTRS1989

Prediction of unsteady rotor-surface heat transfer from wake passings

Predictions using boundary-layer theory with a low-Reynolds number kinetic-energy/dissipation turbulence model are reported for the unsteady heat-flux distributions on the rotor blade surfaces. With an assumed sinusoidal variation for the unsteady surface pressure depicting the effects of convected wake segments, unsteady inviscid-freestream velocity and total enthalpy distributions are determined. Unsteady variations in freestream turbulence due to the wake passings are also considered. The unsteady boundary-layer equations, subject to these freestream conditions, are solved numerically. It was found that most of the unsteady variations in surface heat transfer are due to unsteady pressure changes and not variations in the freestream turbulence. Calculations are made for the Garrett TFE 731-2 HP turbine and the magnitudes of the heat-transfer variations are compared with the measurements of Dunn and Seymour.

Taulbee, Dale B.↗