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At least 1,027 records · Page 57

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NASA NTRS1978

Kinetic model of turbulence in an incompressible fluid

A statistical description of turbulence in an incompressible fluid obeying the Navier-Stokes equations is proposed, where pressure is regarded as a potential for the interaction between fluid elements. A scaling procedure divides a fluctuation into three ranks representing the three transport processes of macroscopic evolution, transport property, and relaxation. Closure is obtained by relaxation, and a kinetic equation is obtained for the fluctuation of the macroscopic rank of the distribution function. The solution gives the transfer function and eddy viscosity. When applied to the inertia subrange of the energy spectrum the analysis recovers the Kolmogorov law and its numerical coefficient.

Tchen, C. M.↗

NASA NTRS1978

Small amplitude waves in a hot relativistic two-fluid plasma

The dispersion relation for small amplitude waves in a hot relativistic plasma embedded in a uniform magnetic field is derived. Four plasma modes exist for propagation oblique to the magnetic field, and the mode properties are summarized in a hot relativistic generalization of the cold plasma pond diagram of Stix (1962). The two-fluid approximation is considered, and two-fluid equations are applied in this procedure which summarizes properties of linear waves in an unbounded magnetized relativistic plasma by means of a parameter-space diagram of wave phase velocity.

Hyun, S.↗

NASA NTRS1979

Magnetohydroelectric waves in a fluid dielectric

An electromagnetic disturbance in a fluid dielectric substance placed in a uniform magnetic field in the positive z direction of a rectangular Cartesian coordinate system with an electric field that increases with time applied in the positive z direction is analyzed. A simultaneous solution to a set of four equations is obtained which indicates a propagating 'magnetohydroelectric' wave that corresponds to oscillations in magnetic, kinetic, and electrostatic energies. It is noted that this wave bears a superficial resemblance to Alfven waves in a magnetized conducting fluid.

De, B. R.↗

NASA NTRS1979

Hydromagnetic interaction in a fluid dielectric

It is shown that a dielectric fluid is capable of hydromagnetic interaction, much like a conducting fluid. The physical principle of this interaction is outlined and the criteria for dominance of the interaction are derived.

De, B. R.↗

NASA NTRS1981

Removing freon gas from hydraulic fluid

Dissolved freon gas is removed from hydraulic fluid by raising temperature to 150 F and bubbling dry nitrogen gas through it, even while fluid circulates through hydraulic system. Procedure reduces parts corrosion, sludge formation, and contamination.

Williams, B. B.↗

NASA NTRS1979

Potential heat exchange fluids for use in sulfuric acid vaporizers

A series of perhalocarbons are proposed as candidate heat exchange fluids for service in thermochemical cycles for hydrogen production that involve direct contact of the fluid with sulfuric acid and vaporization of the acid. The required chemical and physical criteria of the liquids are described and the results of some preliminary high temperature test data are presented.

Lawson, D. D.↗

NASA NTRS1979

Flow and Force Equations for a Body Revolving in a Fluid

A general method for finding the steady flow velocity relative to a body in plane curvilinear motion, whence the pressure is found by Bernoulli's energy principle is described. Integration of the pressure supplies basic formulas for the zonal forces and moments on the revolving body. The application of the steady flow method for calculating the velocity and pressure at all points of the flow inside and outside an ellipsoid and some of its limiting forms is presented and graphs those quantities for the latter forms. In some useful cases experimental pressures are plotted for comparison with theoretical. The pressure, and thence the zonal force and moment, on hulls in plane curvilinear flight are calculated. General equations for the resultant fluid forces and moments on trisymmetrical bodies moving through a perfect fluid are derived. Formulas for potential coefficients and inertia coefficients for an ellipsoid and its limiting forms are presented.

Zahm, A. F.↗

NASA NTRS1979

Potential performance improvement using a reacting gas (nitrogin tetroxide) as the working fluid in a closed Brayton cycle

The results of an analysis to estimate the performance that could be obtained by using a chemically reacting gas (nitrogen tetroxide) as the working fluid in a closed Brayton cycle are presented. Compared with data for helium as the working fluid, these results indicate efficiency improvements from 4 to 90 percent, depending on turbine inlet temperature, pressures, and gas residence time in heat transfer equipment.

Stochl, R. J.↗

NASA NTRS1980

Damping in tapered annular seals for an incompressible fluid

Damping in annular seals is calculated for an incompressible fluid. Results show that damping in tapered seals optimized for stiffness is considerably less than that in straight seals for the same minimum clearance. Damping in rotating seals can promote fractional frequency whirl. Neglecting fluid acceleration makes solution much easier, but leads to errors in calculated damping of up to 16 percent.

Fleming, D. P.↗

NASA NTRS1980

Conceptual design of two-phase fluid mechanics and heat transfer facility for spacelab

Five specific experiments were analyzed to provide definition of experiments designed to evaluate two phase fluid behavior in low gravity. The conceptual design represents a fluid mechanics and heat transfer facility for a double rack in Spacelab. The five experiments are two phase flow patterns and pressure drop, flow boiling, liquid reorientation, and interface bubble dynamics. Hardware was sized, instrumentation and data recording requirements defined, and the five experiments were installed as an integrated experimental package. Applicable available hardware was selected in the experiment design and total experiment program costs were defined.

North, B. F.↗

NASA NTRS1980

Non-Synchronous Whirling Due to Fluid-Dynamic Forces in Axial Turbo-Machinery Rotors

The role of fluid forces acting on the blades of an axial turborotor with regards to whirling was analyzed. The dynamic equations were formulated for the coning mode of an overhung rotor. The exciting forces due to the motion were defined through a set of rotor stability derivatives, and analytical expressions of the aerodynamic contributions were found for the case of small mean stream deflection, high solidity and equivalent flat plate cascade. For a typical case, only backward whirl was indicated when the phase shifting of the rotor wake effect was ignored. A parametric study of the dynamic stability boundary reveals that a reduction in blade stagger angle, mass flow rate, fluid density and an increase in stiffness and external damping are all inductive for improved stability.

Shen, S. F.↗

NASA NTRS1979

Phase change in liquid face seals. II - Isothermal and adiabatic bounds with real fluids

Analytical studies of phase change effects in parallel and tapered liquid face seals are presented. An isothermal and adiabatic model of low Reynolds number flow are considered by numerical integration of the descriptive equations for a real fluid, and its thermodynamic properties are calculated for each step, using a computer program for the steam tables or fluid thermodynamic properties. It was shown that for low leakage rate the isothermal model is more accurate and for high leakage rates the adiabatic model is more accurate; that both models yield the same conclusions regarding stability; and that the transient of collapse is described by the adiabatic model which predicts a catastrophic collapse and then either failure or explosive return to a larger film thickness value. Finally, it is shown that converging seals may become unstable and the mass leakage rate is reduced significantly below the all liquid value when boiling occurs.

Hughes, W. F.↗

NASA NTRS1979

Laminar boundary-layer flow of non-Newtonian fluid

A solution for the two-dimensional and axisymmetric laminar boundary-layer momentum equation of power-law non-Newtonian fluid is presented. The analysis makes use of the Merk-Chao series solution method originally devised for the flow of Newtonian fluid. The universal functions for the leading term in the series are tabulated for n from 0.2 to 2. Equations governing the universal functions associated with the second and the third terms are provided. The solution together with either Lighthill's formula or Chao's formula constitutes a simple yet general procedure for the calculation of wall shear and surface heat transfer rate. The theory was applied to flows over a circular cylinder and a sphere and the results compared with published data.

Lin, F. N.↗

NASA NTRS1980

Measurements of fluid oscillations in isochronous containers

An experiment was designed to measure the fluid oscillations in planar isochronous containers. Measurements of the resonant fluid response to forced oscillations provide direct experimental confirmation of the existence of these special containers.

Weidman, P. D.↗

NASA NTRS1980

Fluid shifts and endocrine responses during chair rest and water immersion in man

The effects of external water pressure on intercompartmental fluid volume shifts and endocrine responses in man are investigated. Extracellular fluid volumes and plasma and urine electrolyte and endocrine responses of four male subjects were measured during eight hours of head-out water immersion and 16 hours of recovery bed rest and compared to responses obtained during eight hours of chair rest and 16 hours of bed rest without external hydrostatic pressure obtained in the same subjects five months later. Immersion is found to result in a substantial diuresis with respect to chair rest, accounted for by decreases in extracellular volume. A negative water balance during immersion and a positive water balance during chair rest were observed to be accompanied by a shift of extracellular volume to the intracellular compartment, as well as the suppression of plasma arginine vasopressin and renin activities in both regimes. The vasopressin and renin activity decreases are attributed to the increased central blood volume, and half of the plasma loss in immersed subjects is attributed to the effects of external water pressure.

Greenleaf, J. E.↗

NASA NTRS1980

Modern fluid dynamics of supersonic and hypersonic flight

Many aspects of fluid dynamics impacting supersonic and hypersonic flight are examined. Progress, current problem areas, and prognostications for the future are discussed, with special emphasis on those fluid dynamics facets which can be more directly tied to a potential end-product vehicle. Numerous illustrative examples are included.

Trimpi, R. L.↗

NASA NTRS1980

A simple numerical orthogonal coordinate generator for fluid dynamic applications

An application of a simple numerical technique which allows for the rapid construction of orthogonal coordinate systems about two dimensional and axisymmetric bodies is presented. The technique is based on a predictor corrector numerical method. It can be used to generate orthogonal meshes which have unequally spaced points in two directions. These orthogonal meshes in their transformed computational plane are, however, equally spaced so that the differencing for the metric coefficients and the fluid dynamic equation terms can be easily determined using equally spaced central finite differences. Solutions to the Navier-Stokes equations for flow over blunt bodies with reverse curvature are presented. The coupling of the time dependent fluid dynamic equations and the coordinate generator worked well with no undesirable effects noted.

Graves, R. A., Jr.↗

NASA NTRS1981

Representative equations for the thermodynamic and transport properties of fluids near the gas-liquid critical point

A survey is presented of representative equations for various thermophysical properties of fluids in the critical region. Representative equations for the transport properties are included. Semi-empirical modifications of the theoretically predicted asymtotic critical behavior that yield simple and practical representations of the fluid properties in the critical region are emphasized.

Sengers, J. V.↗