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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Computation of steady axisymmetric flow using a one-dimensional time-dependent method

An iterative numerical method for computing steady, three dimensional, viscous, compressible flow fields, about aerodynamic bodies was studied. In order to develop the iterative method economically, the primary emphasis was directed towards supersonic, axisymmetric flow. However, the technique readily extends to three spatial dimensions. The viscous flow field about a cone-cylinder-flare body was calculated and compared to existing experimental data. Numerical predictions of the cone boundary layer and the flow field shock wave structure agreed with corresponding measurements. A separation was calculated at the cylinder-flare junction in six iterations; however, the size of the vortex did not correspond to the measured size. It was estimated that fifty iterations would be required to properly define the vortex. It was concluded that the iteration technique is of limited value for plane two dimensional and axisymmetrix flows, but of great value for three-dimensional flows.

Walitt, L.↗
NASA NTRS1984

Calculation of steady and oscillating airfoil flow fields via the Navier Stokes equations

A Navier-Stokes calculation procedure is applied to high Reynolds number flow about steady and unsteady airfoils. The procedure solves the ensemble averaged governing equations via a linearized block implicit (LBI) technique which in general converges to a nominal steady flow within 120 time steps. The grid used in the computation is highly stretched thus resolving the turbulent boundary layers. Calculations have been compared with data for both NACA 4412 airfoil at high incidence and an NACA 0012 airfoil oscillating in dynamic stall. In both cases, good agreement is noted between measured and calculated surface pressure distributions.

Shamroth, S. J.↗
NASA NTRS1939

Intermittent-flow coefficients of a poppet valve

Flow coefficients were determined for the inlet valve of a modern air-cooled cylinder during operation of the valve. The cylinder head with valves was mounted on a large tank that could be evacuated. Operating the valve with a rotating cam allowed air to flow through the valve into the evacuated tank. The change of pressure in the tank was a measure of the amount of air flowing though the valve in a given number of cycles. The flow coefficients were determined from the pressure across the valve, the quantity of air flowing, and the valve-lift curve. Coefficients were measured with lifts of 0.1 to 0.6 inch and speeds of 130 to 1,200 r.p.m. The results obtained with intermittent flow were compared with the results of tests made with steady flow through this cylinder head. This comparison indicated that steady-flow coefficients can be used for intermittent flow.

Waldron, C D↗
NASA NTRS1994

Comments regarding two upwind methods for solving two-dimensional external flows using unstructured grids

Steady flow over the leading portion of a multicomponent airfoil section is studied using computational fluid dynamics (CFD) employing an unstructured grid. To simplify the problem, only the inviscid terms are retained from the Reynolds-averaged Navier-Stokes equations - leaving the Euler equations. The algorithm is derived using the finite-volume approach, incorporating explicit time-marching of the unsteady Euler equations to a time-asymptotic, steady-state solution. The inviscid fluxes are obtained through either of two approximate Riemann solvers: Roe's flux difference splitting or van Leer's flux vector splitting. Results are presented which contrast the solutions given by the two flux functions as a function of Mach number and grid resolution. Additional information is presented concerning code verification techniques, flow recirculation regions, convergence histories, and computational resources.

Kleb, W. L.↗
NASA NTRS1982

Nozzle Modification Suppresses Flow Transients

Proposal for steadying flow from rocket nozzle on Space Shuttle main engine could be applied to other large-area-ratio contoured nozzles. Oscillations and pulsations in boundary-layer flow would be reduced by flaring nozzle exit. Transient side loads on nozzle would be suppressed. Large pressure gradients and eddies that can lead to fluctuations are suppressed. Exact radius of curvature of corner would depend on shear-layer thickness.

Rao, G. V. R.↗
NASA NTRS1986

Turbulent Boundary Layers in Oscillating Flows. Part 1: an Experimental and Computational Study

An experimental-computational study of the behavior of turbulent boundary layers for oscillating air flows over a plane surface with a small favorable mean pressure gradient is described. Experimental studies were conducted for boundary layers generated on the test section wall of a facility that produces a flow with a mean free stream velocity and a superposed nearly-pure sinusoidal component over a wide range of frequency. Flow at a nominal mean free stream velocity of 50 m/s were studied at atmospheric pressure and temperature at selected axial positions over a 2 m test length for frequencies ranging from 4 to 29 Hz. Quantitative experimental results are presented for unsteady velocity profiles and longitudinal turbulence levels obtained from hot wire anemometer measurements at three axial positions. Mean velocity profiles for oscillating flows were found to exhibit only small deviations from corresponding steady flow profiles, while amplitudes and phase relationships exhibited a strong dependence on axial position and frequency. Since sinusoidal flows could be generated over a wide range of frequency, studies at fixed values of reduced frequency at different axial positions were studied. Results show that there is some utility in the use of reduced frequency to correlate unsteady velocity results. The turbulence level u' sub rms was observed to vary essentially sinusoidally around values close to those measured in steady flow. However, the amplitude of oscillation and phase relations for turbulence level were found to be strongly frequency dependent. Numerical predictions were obtained using an unsteady boundary layer computational code and the Cebeci-Smith and Glushko turbulence models. Predicted quantities related to unsteady velocity profiles exhibit fair agreement with experiment when the Cebeci-Smith turbulence model is used.

Cook, W. J.↗
NASA NTRS1988

Computational methods for the problems of the tip vortex

The tip vortex problem for helicopter rotors in transonic flow was studied. The first model was that of potential flow past a single blade in parallel transonic flow. The incidence on the wing of a vortex sheet trailing from a blade in front was studied by modeling the incident sheet by a single vortex filament. A 3-D potential flow code was written to incorporate the usual boundary conditions at infinity together with the model of such a vortex filament and to analyze the resulting flow over the wing. The code was used to study the effect of the vortex filament on the production of shocks at the tip of the wing. Another problem studied within the framework of potential flow theory was the rollup of the vortex sheet behind the wing. A comparison was made of flow models described by the potential equation, by the Euler equations for steady flow, and by the Navier-Stokes equations. The question was also studied as to whether there is an advantage in solving the Navier-Stokes equations rather than the Euler equations for steady flow.

Garabedian, Paul R.↗
NASA NTRS1984

Steady internal flow and aerodynamic loads analysis of shuttle thermal protection system

An analytical model for calculation of ascent steady state tile loading was developed and validated with wind tunnel data. The analytical model is described and results are given. Results are given for loading due to shocks and skin friction. The analysis included calculation of internal flow (porous media flow and channel flow) to obtain pressures and integration of the pressures to obtain forces and moments on an insulation tile. A heat transfer program was modified by using analogies between heat transfer and fluid flow so that it could be used for internal flow calculation. The type of insulation tile considered was undensified reusable surface insulation (RSI) without gap fillers, and the location studied was the lower surface of the orbiter. Force and moment results are reported for parameter variations on surface pressure distribution, gap sizes, insulation permeability, and tile thickness.

Petley, D. H.↗
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 NTRS1977

Effects of inviscid parallel shear flows on steady and unsteady aerodynamics and flutter

A general theory of planar disturbances in inviscid parallel shear flows, analogous to thin-wing theory in potential flows, has been developed. Integral relations between surface pressure and deformation are obtained which are similar to, and can be solved by the same numerical methods as, those of potential flow. Computed results are shown which illustrate the effects of a model turbulent boundary layer on various lifting and nonlifting surfaces, including an elastic panel in low supersonic flow and an airfoil control surface in subsonic flow.

Williams, M. H.↗
NASA NTRS1993

Engineering approach to the prediction of shock patterns in bounded high-speed flows

A two-dimensional symmetric wedge configuration representative of a single high-speed intake in steady flow was investigated. The analysis presented here is intended as an engineering approach for estimating certain features of the internal shock system. The primary interest here is the prediction of the size and location of the almost-normal shock wave that develops when the leading-edge shocks intersect at angles above a certain critical value that is less than the wedge detachment angle. The almost-normal shock wave is frequently referred to as the 'Mach stem', Parametric studies enabled the sensitivity of the Mach stem height to various flowfield parameters to be examined, thus indicating how accurately these parameters must be measured in a given experiment. Results of these predictions were compared with those of a steady-flow experiment performed at nominal freestream Mach numbers from 2.8 to 5. The predicted stem heights were consistently lower than the mean experimental values, attributable both to experimental uncertainties and to certain simplifying assumptions used in the analysis. Modification of these assumptions to better represent the test environment improved the analytical results.

Azevedo, D. J.↗
NASA NTRS1974

A finite difference method for the solution of the transonic flow around harmonically oscillating wings

A finite difference method for the solution of the transonic flow about a harmonically oscillating wing is presented. The partial differential equation for the unsteady transonic flow was linearized by dividing the flow into separate steady and unsteady perturbation velocity potentials and by assuming small amplitudes of harmonic oscillation. The resulting linear differential equation is of mixed type, being elliptic or hyperbolic whereever the steady flow equation is elliptic or hyperbolic. Central differences were used for all derivatives except at supersonic points where backward differencing was used for the streamwise direction. Detailed formulas and procedures are described in sufficient detail for programming on high speed computers. To test the method, the problem of the oscillating flap on a NACA 64A006 airfoil was programmed. The numerical procedure was found to be stable and convergent even in regions of local supersonic flow with shocks.

Ehlers, E. F.↗
NASA NTRS2002

Centrifugal Compressor Surge Margin Improved With Diffuser Hub Surface Air Injection

Aerodynamic stability is an important parameter in the design of compressors for aircraft gas turbine engines. Compression system instabilities can cause compressor surge, which may lead to the loss of an aircraft. As a result, engine designers include a margin of safety between the operating line of the engine and the stability limit line of the compressor. The margin of safety is typically referred to as "surge margin." Achieving the highest possible level of surge margin while meeting design point performance objectives is the goal of the compressor designer. However, performance goals often must be compromised in order to achieve adequate levels of surge margin. Techniques to improve surge margin will permit more aggressive compressor designs. Centrifugal compressor surge margin improvement was demonstrated at the NASA Glenn Research Center by injecting air into the vaned diffuser of a 4:1-pressure-ratio centrifugal compressor. Tests were performed using injector nozzles located on the diffuser hub surface of a vane-island diffuser in the vaneless region between the impeller trailing edge and the diffuser-vane leading edge. The nozzle flow path and discharge shape were designed to produce an air stream that remained tangent to the hub surface as it traveled into the diffuser passage. Injector nozzles were located near the leading edge of 23 of the 24 diffuser vanes. One passage did not contain an injector so that instrumentation located in that passage would be preserved. Several orientations of the injected stream relative to the diffuser vane leading edge were tested over a range of injected flow rates. Only steady flow (nonpulsed) air injection was tested. At 100 percent of the design speed, a 15-percent improvement in the baseline surge margin was achieved with a nozzle orientation that produced a jet that was bisected by the diffuser vane leading edge. Other orientations also improved the baseline surge margin. Tests were conducted at speeds below the design speed, and similar results were obtained. In most cases, the greatest improvement in surge margin occurred at fairly low levels of injected flow rate. Externally supplied injection air was used in these experiments. However, the injected flow rates that provided the greatest benefit could be produced using injection air that is recirculating between the diffuser discharge and nozzles located in the diffuser vaneless region. Future experiments will evaluate the effectiveness of recirculating air injection.

Skoch, Gary J.↗
NASA NTRS2013

Current Flow and Pair Creation at Low Altitude in Rotation-Powered Pulsars' Force-Free Magnetospheres: Space Charge Limited Flow

We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs.We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 < j/j(sub GJ) < 1), space charge limited acceleration of the current carrying beam is mild, with the full Goldreich-Julian charge density comprising the charge densities of the beam and a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are of the order of mc(sup 2)/e, and pair creation is absent. (b) When the current density exceeds the Goldreich-Julian value (j/j(sub GJ) > 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/j(sub GJ) < 0, the system develops similar bursts of pair creation. These discharges are similar to those encountered in previous calculations by Timokhin of pair creation when the surface has a high work function and cannot freely emit charge. In cases (b) and (c), the intermittently generated pairs allow the system to simultaneously carry the magnetospherically prescribed currents and adjust the charge density and average electric field to force-free conditions. We also elucidate the conditions for pair creating beam flow to be steady (stationary with small fluctuations in the rotating frame), finding that such steady flows can occupy only a small fraction of the current density parameter space exhibited by the force-free magnetospheric model. The generic polar flow dynamics and pair creation are strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage (with pair creation, when the voltage drops are sufficiently large; without, when they are small) as a function of the applied current.

Timokhin, A. N.↗
NASA NTRS1930

Flow and Force Equations for a Body Revolving in a Fluid

Part I gives 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. Integration of the pressure supplies basic formulas for the zonal forces and moments on the revolving body. Part II, applying this steady-flow method, finds the velocity and pressure at all points of the flow inside and outside an ellipsoid and some of its limiting forms, and graphs those quantities for the latter forms. Part III finds the pressure, and thence the zonal force and moment, on hulls in plane curvilinear flight. Part IV derives general equations for the resultant fluid forces and moments on trisymmetrical bodies moving through a perfect fluid, and in some cases compares the moment values with those found for bodies moving in air. Part V furnishes ready formulas for potential coefficients and inertia coefficients for an ellipsoid and its limiting forms. Thence are derived tables giving numerical values of those coefficients for a comprehensive range of shapes.

Zahm, A F↗
NASA NTRS2002

Temporal gradients in shear stimulate osteoblastic proliferation via ERK1/2 and retinoblastoma protein

Bone cells are subject to interstitial fluid flow (IFF) driven by venous pressure and mechanical loading. Rapid dynamic changes in mechanical loading cause transient gradients in IFF. The effects of pulsatile flow (temporal gradients in fluid shear) on rat UMR106 cells and rat primary osteoblastic cells were studied. Pulsatile flow induced a 95% increase in S-phase UMR106 cells compared with static controls. In contrast, ramped steady flow stimulated only a 3% increase. Similar patterns of S-phase induction were also observed in rat primary osteoblastic cells. Pulsatile flow significantly increased relative UMR106 cell number by 37 and 62% at 1.5 and 24 h, respectively. Pulsatile flow also significantly increased extracellular signal-regulated kinase (ERK1/2) phosphorylation by 418%, whereas ramped steady flow reduced ERK1/2 activation to 17% of control. Correspondingly, retinoblastoma protein was significantly phosphorylated by pulsatile fluid flow. Inhibition of mitogen-activated protein (MAP)/ERK kinase (MEK)1/2 by U0126 (a specific MEK1/2 inhibitor) reduced shear-induced ERK1/2 phosphorylation and cell proliferation. These findings suggest that temporal gradients in fluid shear stress are potent stimuli of bone cell proliferation.

NASA Discipline Cell Biology↗
NASA NTRS1986

On the Lagrangian Method for Steady and Unsteady Flow

A new and general Lagrangian formulation of fluid motion is given in which the independent variables are three material functions and a Lagrangian time, which differs for different fluid particles and is distinct from the Eulerian time. For steady flow it requires only three independent variables - the Lagrangian time and two stream functions - in contrast with the conventional Lagrangian formulation which apparently still requires four independent variables for describing a steady flow. This places the Lagrangian formulation for steady flow on the same footing as the Eulerian. For unsteady flow, the new formulation includes the conventional formulation as a special case when the Lagrangian time is identified with the Eulerian time and when the material functions are taken to be the fluid particle's position at some given time. The distinction between the Lagrangian and Eulerian time, however, is found useful in applications, e.g., to problems involving a free boundary.

Hui, W. H.↗
NASA NTRS1993

Unsteady Flow Simulations in Support of the SSME HEX Turning Vane Cracking Investigation with the ATD HPOTP

Unsteady flow computations are being performed with the P&W (ATD) and the Rocketdyne baseline configurations of the SSME LO2 turbine turnaround duct (TAD) and heat exchanger (HEX). The work is in support of the HEX inner turning vane cracking investigation. Fatigue cracking has occurred during hot firings with the P&W configuration on the HEX inner vane, and it appears the fix will involve changes to the TAD splitter vane position and to the TAD inner wall curvature to reduce the dynamic loading on the inner vane. Unsteady flow computations on the P&W baseline and fix and on the Rocketdyne baseline reference follow steady-flow screening computations done by MSFC/ED32 on several trial configurations arriving at the fix. The P&W TAD inlet velocity profile has a strong radial velocity component that directs the flow toward the inner wall and raises the local velocity a factor of two and the dynamic pressure a factor, of four. The fix is intended to redistribute the flow more evenly across the HEX inner and outer vanes like the Rocketdyne baseline reference. Vane buffeting at frequencies around 4,000 Hz is the leading suspected cause of the problem. Our simulations (work in progress) are being done with the USA 2D axisymmetric code approximating the flow as axisymmetric u+v 2D (axial, u, and radial, v, components only). The HEX coils are included in the model to make sure the fix does not adversely affect the HEX environment. Turbulent kinetic energy, k, levels where k = 1/2 v' rms2 are locally as high as 10,000 ft2/sec2 for the P&W baseline at the engine interface (between the TAD and HEX) at the HEX inner vane location. However, k is less than 8,000 on the HEX outer vane and only about 4,500 on the HEX inner vane for the Rocketdyne baseline. Unsteady turbulence intensity, v'rms/v, and pressure, p', are being computed in the present computations to compare with steady-flow Reynolds-averaged computations where p'rms = const (pk) for overall rms random turbulence from 0.1 to 12,000 Hz frequency. Random overall static, p'rms fluctuations as large as 1.7 psi are estimated from k on the HEX inner vane for the P&W baseline configuration but only about 0.7 psi for the Rocketdyne configuration.

Dougherty, N. S.↗