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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

An experimental study of a three-dimensional shock wave/turbulent boundary-layer interaction at a hypersonic Mach number

Experimental data for a series of three-dimensional shock-wave/turbulent-boundary-layer interaction flows at Mach 8.2 are presented. The test bodies, composed of sharp fins fastened to a flat-plate test surface, were designed to generate flows with varying degrees of pressure gradient, boundary-layer separation, and turning angle. The data include surface-pressure, heat-transfer, and skin-friction distributions, as well as limited mean flowfield surveys both in the undisturbed and interaction regimes. The data were obtained for the purpose of validating computational models of these hypersonic interactions.

Kussoy, M. I.↗
NASA NTRS1992

Pressure drop in fully developed, turbulent, liquid-vapor annular flows in zero gravity

The prediction of frictional pressure drop in fully developed, turbulent, annular liquid-vapor flows in zero gravity using simulation experiments conducted on earth is described. The scheme extends the authors' earlier work on dispersed flows. The simulation experiments used two immiscible liquids of identical density, namely, water and n-butyl benzoate. Because of the lack of rigorous analytical models for turbulent, annular flows, the proposed scheme resorts to existing semiempirical correlations. Results based on two different correlations are presented and compared. Others may be used. It was shown that, for both dispersed and annular flow regimes, the predicted frictional pressure gradients in 0-g are lower than those in 1-g under otherwise identical conditions. The physical basis for this finding is given.

Sridhar, K. R.↗
NASA NTRS1993

Evaluation of Baldwin-Barth turbulence model with thin-layer Navier-Stokes computation of an axisymmetric afterbody-exhaust jet flowfield

Axisymmetric steady flowfield over a steep circular arc afterbody with a choked exhaust jet in a subsonic freestream is numerically investigated using overflow code, developed by NASA Ames. The accuracy of Baldwin-Barth one-equation turbulence model for the computation of separated flow and plume shear layers is assessed by a comparison of predictions with available measurements from NASA Langley. The results show that the Baldwin-Barth turbulence model performs better than the Baldwin-Lomax algebraic model in predicting the surface pressure distribution in the separated flow region of the afterbody. In the jet mixing layer, the Baldwin-Barth model considerably unpredicts the growth of the shear layer, as does the Baldwin-Lomax model. It is shown that the one-equation turbulence model needs improvement for the prediction of separated flow due to smooth adverse pressure gradient, and mixing layer growth.

Kandula, M.↗
NASA NTRS1993

Three-dimensional hypersonic shock wave/turbulent boundary-layer interactions

Experimental data for a series of three-dimensional shock wave/turbulent boundary-layer interaction flows at Mach 8.2 are presented. The test bodies, composed of sharp fins fastened to a flat plate test surface, were designed to generate flows with varying degrees of pressure gradient, boundary-layer separation, and turning angle. The data include surface pressure, heat transfer, and skin friction distributions as well as limited mean flowfield surveys in both the undisturbed and interaction regimes. The data were obtained for the purpose of validating computational models of these hypersonic interactions.

Kussoy, M. I.↗
NASA NTRS1993

Features of a SINDA/FLUINT model of a liquid oxygen supply line

The modeling features used in a steady-state heat transfer problem using SINDA/FLUINT are described. The problem modeled is a 125 feet long, 3 inch diameter pipe, filled with liquid oxygen flow driven by a given pressure gradient. The pipe is fully insulated in five sections. Three sections of 1 inch thick spray-on foam and two sections of vacuum jacket. The model evaluates friction, turns losses and convection heat transfer between the fluid and the pipe wall. There is conduction through the foam insulation with temperature dependent thermal conductivity. The vacuum space is modeled with radiation and gas molecular conduction, if present, in the annular gap. Heat is transferred between the outer surface and surrounding ambient by natural convection and radiation; and, by axial conduction along the pipe and through the vacuum jacket spacers and welded seal flanges. The model makes extensive use of SINDA/FLUINT basic capabilities such as the GEN option for nodes and conductors (to generate groups of nodes or conductors), the SIV option (to generate single, temperature varying conductors), the SIM option (for multiple, temperature varying conductors) and the M HX macros for fluids (to generate strings of lumps, paths, and ties representing a diabatic duct). It calls subroutine CONTRN (returns the relative location in the G-array of a network conductor, given an actual conductor number) enabling an extensive manipulation of conductor (calculates an assignment of their values) with DO loops. Models like this illustrate to the new and even to the old SINDA/FLUINT user, features of the program that are not so obvious or known, and that are extremely handy when trying to take advantage of both, the automation of the DATA headers and make surgical modifications to specific parameters of the thermal or fluid elements in the OPERATIONS portion of the model.

Simmonds, Boris G.↗
NASA NTRS1995

USML-1 Glovebox experiments

This report covers the development of and results from three experiments that were flown in the Materials Science Glovebox on USML-1: Marangoni convection in Closed Containers (MCCC), Double Float Zone (DFZ), and Fiber Pulling in Microgravity (FPM). The Glovebox provided a convenient, low cost method for doing simple 'try and see' experiments that could test new concepts or elucidate microgravity phenomena. Since the Glovebox provided essentially one (or possibly two levels of confinement, many of the stringent verification and test requirements on the experiment apparatus could be relaxed and a streamlined test and verification plan for flight qualification could be implemented. Furthermore, the experiments were contained in their own carrying cases whose external configurations could be identified early in the integration sequence for stowage considerations while delivery of the actual experiment apparatus could be postponed until only a few months before flight. This minimized the time fluids must be contained and reduced the possibility of corrosive reactions that could ruin the experiment. In many respects, this exercise was as much about developing a simpler, cheaper way of doing crew-assisted science as it was about the actual scientific accomplishments of the individual experiments. The Marangoni Convection in Closed Containers experiment was designed to study the effects of a void space in a simulated Bridgman crystal growth configuration and to determine if surface tension driven convective flows that may result from thermal gradients along any free surfaces could affect the solidification process. The Fiber Pulling in Microgravity experiment sought to separate the role of gravity drainage from capillarity effects in the break-up of slender cylindrical liquid columns. The Stability of a Double Float Zone experiment explored the feasibility of a quasi-containerless process in which a solidifying material is suspended by two liquid bridges of its own melt.

Naumann, Robert J.↗
NASA NTRS1995

Early time evolution of a chemically produced electron depletion

The early time evolution of an ionospheric electron depletion produced by a radially expanding electron attachment chemical release is studied with a two-dimensional simulation model. The model includes electron attachment chemistry, incorporates fluid electrons, particle ions and neutrals, and considers the evolution in a plane perpendicular to the geomagnetic field for a low beta plasma. Timescales considered are of the order of or less than the cyclotron period of the negative ions that result as a by-product of the electron attacment reaction. This corresponds to time periods of tenths of seconds during recent experiemts. Simulation results show that a highly sheared azimuthal electron flow velocity develops in the radially expanding depletion boundary. This sheared electron flow velocity and the steep density gradients in the boundary give rise to small-scale irregulatities in the form of electron density cavities and spikes. The nonlinear evolution of these irregularities results in trapping and ultimately turbulent heating of the negative ions.

Scales, W. A.↗
NASA NTRS1996

Magnetothermal Convection in Nonconducting Diamagnetic and Paramagnetic Fluids

Nonuniform magnetic fields exert a magnetic body force on electrically nonconducting classical fluids. These include paramagnetic fluids such as gaseous and liquid oxygen and diamagnetic fluids such as helium. Recent experiments show that this force can overwhelm the force of gravity even at the surface of the earth; it can levitate liquids and gases, quench candle flames, block gas flows, and suppress heat transport. Thermal gradients render the magnetic force nonuniform through the temperature-dependent magnetic susceptibility. These thermal gradients can therefore drive magnetic convection analogous to buoyancy-driven convection. This magnetothermal convection can overwhelm convection driven by gravitational buoyancy in terrestrial experiments. The objectives of the proposed ground-based theoretical study are (a) to supply the magnetothermohydrodynamic theory necessary to understand these recent experiments and (b) to explore the consequences of nonuniform magnetic fields in microgravity. Even the linear theory for the onset of magnetothermal convection is lacking in the literature. We intend to supply the linear and nonlinear theory based on the thermohydrodynamic equations supplemented by the magnetic body force. We intend to investigate the effect of magnetic fields on gas blockage and heat transport in microgravity. Since magnetic fields provide a means of creating arbitrary, controllable body force distributions, we intend to investigate the possibility of using magnetic fields to position and control fluids in microgravity. We also intend to investigate the possibility of creating stationary terrestrial microgravity environments by using the magnetic force to effectively cancel gravity. These investigations may aid in the design of space-based heat-transfer, combustion, and human-life-support equipment.

Edwards, Boyd F.↗
NASA NTRS1981

Application of a Laser Interferometer Skin-Friction Meter in Complex Flows

A nonintrusive skin-friction meter has been found useful for a variety of complex wind-tunnel flows. This meter measures skin friction with a remotely located laser interferometer that monitors the thickness change of a thin oil film. Its accuracy has been proven in a low-speed flat-plate flow. The wind-tunnel flows described here include sub-sonic separated and reattached flow over a rearward-facing step, supersonic flow over a flat plate at high Reynolds numbers, and supersonic three - dimensional vortical flow over the lee of a delta wing at angle of attack. The data-reduction analysis was extended to apply to three-dimensional flows with unknown flow direction, large pressure and shear gradients, and large oil viscosity changes with time. The skin friction measurements were verified, where possible, with results from more conventional techniques and also from theoretical computations.

Monson, D. J.↗
NASA NTRS1980

Mach and Reynolds Number Effects on a Shock-Wave/Boundary-Layer Interaction

The present investigation was undertaken as part of a continuing experimental/numerical program to evaluate and improve turbulence models for use in Navier-Stokes (N-S) codes. The normal shock-wave/turbulent boundary-layer interaction is a good test for such computations because it contains strong adverse pressure gradients and the possibility of local flow separation. Since constraints must be included in any computational scheme, methods employing the N-S equations are attractive because simultaneous treatment of both the viscous and inviscid flowfields is possible. The evolution of N-S codes is based primarily upon the development of models for the turbulence terms in these equations.

Mateer, G. G.↗
NASA NTRS1999

Lean Premixed Combustion Stabilized by Low Swirl a Promising Concept for Practical Applications

Since its inception, the low-swirl burner (LSB) has shown to be a useful laboratory apparatus for fundamental studies of premixed turbulent flames. The LSB operates under wide ranges of equivalence ratios, flow rates, and turbulence intensities. Its flame is lifted and detached from the burner and allows easy access for laser diagnostics. The flame brush is axisymmetric and propagates normal to the incident reactants. Therefore, the LSB is well suited for investigating detailed flame structures and empirical coefficients such as flame speed, turbulence transport, and flame generated turbulence. Due to its capability to stabilize ultra-lean premixed turbulent flames (phi approx. = 0.55), the LSB has generated interest from the gas appliance industry for use as an economical low-NO(x) burner. Lean premixed combustion emits low levels of NO(x), due primarily to the low flame temperature. Therefore, it is a very effective NO(x) prevention method without involving selective catalytic reduction (SCR), fuel-air staging, or flue gas recirculation (FGR). En the gas turbine industry, substantial research efforts have already been undertaken and engines with lean premixed combustors are already in use. For commercial and residential applications, premixed pulsed combustors and premixed ceramic matrix burners are commercially available. These lean premixed combustion technologies, however, tend to be elaborate but have relatively limited operational flexibility, and higher capital, operating and maintenance costs. Consequently, these industries are continuing the development of lean premixed combustion technologies as well as exploring new concepts. This paper summarizes the research effects we have undertaken in the past few years to demonstrate the feasibility of applying the low-swirl flame stabilization method for a wide range of heating and power generation systems. The principle of flame stabilization by low-swirl is counter to the conventional high-swirl methods that rely on a recirculation zone to anchor the flame. In LSBS, flow recirculation is not promoted to allow the premixed turbulent flames to propagate freely. A LSB with an air-jet swirler is essentially an open tube with the swirler at its mid section. The small air-jets generate swirling motion only in the annular region and leaving the central core of the flow undisturbed, When this flow exits the burner tube, the angular momentum generates radial mean pressure gradient to diverge the non-swirling reactants stream. Consequently, the mean flow velocity decreases linearly. Propagating against this decelerating flow, the flame self-sustains at the position where the local flow velocity equals the flame speed, S(sub f). The LSB operates with a swirl number, S, between 0.02 to 0.1. This is much lower than the minimum S of 0.6 required for the high-swirl burners. We found that the swirl number needed for flame stabilization varies only slightly with fuel type, flow velocity, turbulent conditions and burner dimensions (i.e. throat diameter and swirl injection angle).

Cheng, R. K.↗
NASA NTRS1997

Analysis, Repair, and Management of the Total Ozone Mapping Spectrometer Database

In the ensuing period we were able to demonstrate that the origin of these filamentous patterns resulted from the action of synoptic-scale vortical velocity field on the global-scale background gradient of ozone concentration in the meridional direction. Hyperbolic flow patterns between long-lived atmospheric vortices bring together air parcels from different latitudes, thus creating large gradients along the separatrices leaving the hyperbolic (stagnation) point. This result is further confirmed by the KL analysis of the ozone field in the equatorial region, where the background concentration gradient vanishes. The spectral slope in this region has been found to lie close to -1, in agreement with Batchelor's prediction. Another outcome of this result is that it at least provides indirect evidence about the kinetic energy spectrum of the atmospheric turbulence in the range of scales approximately 200 to 2000 km. Namely, Batchelor's analysis is based on the assumption that the velocity field is large-scale, that is the kinetic energy spectrum decays as O(k(sup -3)) or steeper. Since the scalar spectrum is confirmed, this also supports this form of the kinetic energy spectrum. The study of equatorial regions of TOMS data revealed the efficiency of the KL method is in detecting and separating a wave-like measurement artifact inherently present in the dataset due to the non-perfect correction for cross-track bias. Just two to three eigenfunctions represent the error, which makes it possible to enhance the data by reconstituting it from the data by eliminating the subspace of artifactual eigenfunctions. This represents a highly efficient means for achieving an improved rendering of the data. This has been implemented on the database. A wide range of techniques and algorithms have been developed for the repair and extension of the TOMS database.

Sirovich, Lawrence↗
NASA NTRS2002

Steady State Sedimentation in a Liquid Fluidized Bed

The velocity fluctuations and the local particle concentration of a particle suspension exhibiting steady state sedimentation in a fluidized bed are determined as a function of height along the particle column. Both the velocity fluctuations and the particle volume fraction are found to strongly depend on height. We account for the stability of the bed by a simple model evoking a flux balance. Velocity fluctuations driving a downward particle flux are compensated by an upward particle flux stemming from an excess flow velocity due to the concentration gradient of the system.

Segre, P. N.↗
NASA NTRS2004

Computation of Sensitivity Derivatives of Navier-Stokes Equations using Complex Variables

Accurate computation of sensitivity derivatives is becoming an important item in Computational Fluid Dynamics (CFD) because of recent emphasis on using nonlinear CFD methods in aerodynamic design, optimization, stability and control related problems. Several techniques are available to compute gradients or sensitivity derivatives of desired flow quantities or cost functions with respect to selected independent (design) variables. Perhaps the most common and oldest method is to use straightforward finite-differences for the evaluation of sensitivity derivatives. Although very simple, this method is prone to errors associated with choice of step sizes and can be cumbersome for geometric variables. The cost per design variable for computing sensitivity derivatives with central differencing is at least equal to the cost of three full analyses, but is usually much larger in practice due to difficulty in choosing step sizes. Another approach gaining popularity is the use of Automatic Differentiation software (such as ADIFOR) to process the source code, which in turn can be used to evaluate the sensitivity derivatives of preselected functions with respect to chosen design variables. In principle, this approach is also very straightforward and quite promising. The main drawback is the large memory requirement because memory use increases linearly with the number of design variables. ADIFOR software can also be cumber-some for large CFD codes and has not yet reached a full maturity level for production codes, especially in parallel computing environments.

Vatsa, Veer N.↗
NASA NTRS2006

Real-Time Feedback Control of Flow-Induced Cavity Tones: Adaptive Control - Part 2

An adaptive generalized predictive control (GPC) algorithm was formulated and applied to the cavity flow-tone problem. The algorithm employs gradient descent to update the GPC coefficients at each time step. Past input-output data and an estimate of the open-loop pulse response sequence are all that is needed to implement the algorithm for application at fixed Mach numbers. Transient measurements made during controller adaptation revealed that the controller coefficients converged to a steady state in the mean, and this implies that adaptation can be turned off at some point with no degradation in control performance. When converged, the control algorithm demonstrated multiple Rossiter mode suppression at fixed Mach numbers ranging from 0.275 to 0.38. However, as in the case of fixed-gain GPC, the adaptive GPC performance was limited by spillover in sidebands around the suppressed Rossiter modes. The algorithm was also able to maintain suppression of multiple cavity tones as the freestream Mach number was varied over a modest range (0.275 to 0.29). Beyond this range, stable operation of the control algorithm was not possible due to the fixed plant model in the algorithm.

Kegerise, M. A.↗
DOE OSTI2024

Retrofittable Thermal Switches for Dynamic Building Envelopes Integrated with Thermal Energy Storage: Preprint

Buildings in the United States consume about 40 quadrillion BTU of primary energy annually, which accounts for the nation's 40% of total energy use, 75% of all electricity use, and 35% of the net carbon emissions. Deploying thermal energy storage in the form of phase change material (PCM) in building envelopes is an effective method to reduce space heating/cooling loads, provide load shedding, and shift demand to periods of lower energy cost. However, the full potential of PCM-integrated envelopes can only be realized if the PCM undergoes complete phase change using free ambient heating/cooling, and the stored energy is effectively transferred between the exterior and the interior environments. Conventional thermal insulation (with a fixed thermal resistance) limits PCM utilization, particularly with the increasing emphasis on higher R-value in building envelopes, which negatively affects the energy-saving potential of a PCM-integrated envelope. In contrast, dynamic building envelopes integrated with PCMs provide the option of varying the thermal resistance based on the indoor and outdoor conditions, thereby enhancing utilization of free ambient cooling and heating to charge/discharge the PCM thermal storage, reducing the buildings' heating and cooling load, and shifting the peak energy demand. In this study, we demonstrate innovative retrofittable thermal switches in the form of the insertable plugs inside an insulation to provide variable thermal resistance depending on the operating temperature and direction of temperature gradient, thus allowing preferential directional heat flow. Notably, they are passive in nature, requiring no external power, and work solely based on the ambient temperature.

buildings↗
NASA NTRS1984

Computational-experimental pressure distributions on a transonic, low-aspect-ratio wing

A generic, transonic, supercritical, low aspect-ratio wing was tested at design incidence of 5 deg at Mach numbers from 0.25 to 0.96. Oil-flow studies at the design Mach number of 0.85 showed local-flow separation, which, in retrospect, might have been avoided. At Mach 0.82 with unseparated flow, the surface-flow angles were less than 10 deg. Predictions with the FLO22 transonic potential code are good. Lift interference is strong without tunnel-wall suction. Evidence from this study shows that wings that are optimized for mild shock waves and pressure-recovery gradients generally have small, three-dimensional flow at conditions for unseparated flow.

Keener, E. R.↗
NASA NTRS1990

Three-dimensional potential flows from functions of a 3D complex variable

Potential, or ideal, flow velocities can be found from the gradient of an harmonic function. An ordinary complex valued analytic function can be written as the sum of two real valued functions, both of which are harmonic. Thus, 2D complex valued functions serve as a source of functions that describe two-dimensional potential flows. However, this use of complex variables has been limited to two-dimensions. Recently, a new system of three-dimensional complex variables has been developed at the NASA Ames Research Center. As a step toward application of this theory to the analysis of 3D potential flow, several functions of a three-dimensional complex variable have been investigated. The results for two such functions, the 3D exponential and 3D logarithm, are presented in this paper. Potential flows found from these functions are investigated. Important characteristics of these flows fields are noted.

Kelly, Patrick↗