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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.

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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Conical diffuser for fuel cells

Diffuser is inserted into inlet manifold, producing smooth transition of flow from pipe diameter to manifold diameter. Expected pressure gradient and resulting cell-to-cell temperature gradient are reduced. Outlet manifold has nozzle insert that reduces exit losses.

Craft, D. W.↗
NASA NTRS1978

A systems approach to theoretical fluid mechanics: Fundamentals

A preliminary application of the underlying principles of the investigator's general system theory to the description and analyses of the fluid flow system is presented. An attempt is made to establish practical models, or elements of the general fluid flow system from the point of view of the general system theory fundamental principles. Results obtained are applied to a simple experimental fluid flow system, as test case, with particular emphasis on the understanding of fluid flow instability, transition and turbulence.

Anyiwo, J. C.↗
NASA NTRS1979

Fundamental mechanisms that influence the estimate of heat transfer to gas turbine blades

Heat tranfer problems in aircraft gas turbines required for improved prediction of turbine blade or vane gas-side heat transfer are examined. Estimates of the heat transfer from the gas to vanes or rotating blades are uncertain due to the complexity of the heat transfer processes, since the gas flow is three dimensional with complex secondary viscous flow patterns that interact with the endwalls and blade surfaces. In addition, upstream disturbances, stagnation flow, curvature effects, and flow acceleration complicate the thermal transport mechanisms in the boundary layers. The thermal state and flow characteristics of the hot gases that enter the turbine blade row, analytical methods for calculating the gas-side heat transfer to turbine blades, and flow phenomena such as stagnation, curvature effects, acceleration, secondary flows, and transition that influences local heat transfer rates are discussed.

Graham, R. W.↗
NASA NTRS1982

Cool luminous stars

The consequences of magnetic fields for the atmospheres of cool stars are addressed based on IUE and Einstein Observatory observations. Gross atmospheric structure data for cool luminous stars are discussed, and the relevance of the observations for the energy balance and nonradiative heating rates is considered. Data from X-ray fluxes, low dispersion UV spectra, and high dispersion spectra in the region of the Mg II resonance lines are presented. New results on cool star atmospheres provided by high dispersion UV spectra are considered, including those pertaining to spectral line identification, identification of emission components in close binary systems, densities and atmospheric extension, emission line widths, properties of stellar winds as derived from IUE data, and systematic flows of transition region plasma. An explanation for the observed spectra of cool giants and supergiants is proposed in terms of active, quiet, and hybrid stars.

Linsky, J. L.↗
NASA NTRS1983

Fluid motions in the solar chromosphere-corona transition region. III - Active region flows from wide slit Dopplergrams

Large-scale velocity patterns observed in C IV in active regions show close correspondence with photospheric magnetic field patterns. In a large majority of cases, magnetic neutral lines show blueshift on their sun center side and redshift on their limbward side. The large-scale flow is consistent with widespread loop structure having downflow in both legs of the loops. Studies of individual bright loops, confirm that the flow is downward in most cases. However, an important subset of loops show flow from one end of the loop to the other.

Athay, R. G.↗
NASA NTRS1985

Wave-mean flow interaction during the winter to summer transition in the Southern Hemisphere stratosphere

The evolution of the flow and wave-mean flow interactions in the Southern Hemisphere during the period when the final stratospheric warming and the associated reversal of the flow in the upper stratosphere occurred is described. The spring is the most interesting season as far as the wave mean flow interaction in the Southern Hemisphere is concerned. The data for this study are NMC analysis of temperature and geopotential fields between 1000 and 0.45 mb for the period August 31 to November 10, 1979.

Yamazaki, K.↗
NASA NTRS1986

Navier-Stokes computations of lee-side flows over delta wings

Solutions to the Navier-Stokes equations for the flow over delta wings are computed with emphasis on the separated vortical flows developing on the lee side at high angles of attack. A recently developed implicit algorithm is used which employs upwind differencing for the pressure and convection terms and central differencing for the shear stress and heat transfer terms. Solutions to both the three-dimensional equations and the approximate conical flow equations are compared parametrically with an extensive experimental data base at supersonic speeds. The computations indicate that the conical flow approximation provides results in close agreement with the three-dimensional equations, even to angles of attack as high as 20 degrees. Good agreement with experimentally measured pressures and vapor screen photographs is obtained for the conditions investigated. The method predicts the classical pattern of vortical flow over a delta wing and transition to other flow patterns as the leading edge sweep angle and leading edge normal Mach number are varied.

Thomas, J. L.↗
NASA NTRS1989

Coherent structures in transitional and turbulent free shear flows

The development of a quantitative understanding of large-scale coherent structures in shear flows has led to the recognition of their evolutionary features and 'rules' of nonlinear interaction among each other. These determinations, in conjunction with the study of fine-grained turbulence and mean motion, constitute a general view of hydrodynamical instabilities that has resulted in useful concepts for the achievement of shear-flow control. The dynamical role of longitudinal structures in free shear flows is presently exemplified by the axisymmetric and helical modes in a round jet, which resemble the two-dimensional and spanwise-periodic three-dimensional modes in a two-dimensional mean flow.

Liu, J. T. C.↗
NASA NTRS1989

Aerodynamic applications of infrared thermography

A series of wind tunnel experiments were conducted as part of a systematic study for evaluation of infrared thermography as a viable non-intrusive thermal measurement technique for aerodynamic applications. The experiments consisted of obtaining steady-state surface temperature and convective heat transfer rates for a uniformly heated cylinder in transverse flow with a Reynolds number range of 46,000 to 250,000. The calculated convective heat transfer rates were in general agreement with classical data. Furthermore, IR thermography provided valuable real-time fluid dynamic information such as visualization of flow separation, transition and vortices.

Daryabeigi, Kamran↗
NASA NTRS1992

Thermal stability during rotation in space - A scaling and numerical analysis

An analysis of thermal stability in a fluid during rotation is presented. The conditions resulting in thermal stability are examined and numerically verified. It is shown that at least one thermal field exists for any rotating fluid, with or without a gravitational background field, where convection does not occur. The numerical model used is fully nonlinear and 3D. Results are presented on the basis of both steady-state and fully transient models. The thermally stable condition is further investigated in the context of the average net acceleration and the inhomogeneous part of the acceleration field (gradient of acceleration). It is shown that in the thermally stable condition the flow that would result from the average net acceleration is equal and opposite to the flow that would result from the inhomogeneous part of the acceleration field. It is concluded that the thermally stable condition is actually a flow mode transition at Ad = 1.

Arnold, William A.↗
NASA NTRS1987

Research on complex turbulent flows at the UW (overall effort)

Development of a pressure-strain model, an algebraic stress model, and wall functions appropriate for flows with spanwise variations in the local wall shear stress are accomplished. Furthermore, a hot-wire measurement technique was also developed for determining the local mean velocity and Reynolds stresses in a complex flow. Experiments were performed on supersonic and subsonic turbulent flow in a square duct, flow about a strut-endwall, flow within a transition duct, and on co-flowing annular jets with swirl. All results are presented in a viewgraph format.

Gessner, F. B.↗
NASA NTRS1993

Prediction of gas-liquid two-phase flow regime in microgravity

An attempt is made to predict gas-liquid two-phase flow regime in a pipe in a microgravity environment through scaling analysis based on dominant physical mechanisms. Simple inlet geometry is adopted in the analysis to see the effect of inlet configuration on flow regime transitions. Comparison of the prediction with the existing experimental data shows good agreement, though more work is required to better define some physical parameters. The analysis clarifies much of the physics involved in this problem and can be applied to other configurations.

Lee, Jinho↗
NASA NTRS1993

Scaling analysis of gas-liquid two-phase flow pattern in microgravity

A scaling analysis of gas-liquid two-phase flow pattern in microgravity, based on the dominant physical mechanism, was carried out with the goal of predicting the gas-liquid two-phase flow regime in a pipe under conditions of microgravity. The results demonstrated the effect of inlet geometry on the flow regime transition. A comparison of the predictions with existing experimental data showed good agreement.

Lee, Jinho↗
NASA NTRS1993

Surface hot-film method for the measurement of transition, separation and reattachment points

A real-time method of determining positions of laminar-to-turbulent transition region, separation and reattachment points and stagnation points using an array of simultaneously operated surface-mounted hot-film sensors has been developed and applied to a wind-tunnel test of a multielement airfoil model. Determination of various types of transitions and flow directions in various regimes of flows seen on multielement airfoils are possible without precise sensor calibration or laborious post-test data analysis. The results agree with established method and theoretical methods, but determination of turbulent reattachment points are not yet satisfactory.

Nakayama, Akihiko↗