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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Ion-neutral momentum coupling near discrete high-latitude ionospheric features

A two-dimensional numerical model is developed to study the momentum coupling between the ionosphere and neutral atmosphere in the vicinity of discrete high-latitude features, such as convection channels and plasma density troughs. Based on generalized magnetohydrodynamic equations the model takes account of global pressure gradients, viscous dissipation, ion drag, the Coriolis force, and electrodynamic drifts. Among the findings of an initial steady state investigation are the following: (1) in convection channels, significant shears and rotations of the thermospheric flow can occur below 200 km if a minimum in the electron density profile is present between the E and F regions; (2) in convection channels, the thermospheric wind decreases with height in the F region owing to the effects of horizontal viscosity; and (3) at low altitudes, the boundaries of convection channels may produce Ekman spirals.

St-Maurice, J.-P.↗
NASA NTRS1985

Numerical simulation in three space dimensions of time-dependent thermal convection in a rotating fluid

Three-dimensional time-dependent convection in a plane layer of fluid, uniformly heated from below and subject to vertical shear and to rotation about an axis tilted from the vertical, was simulated by the numerical solution of the Boussinesq equations, including all Coriolis terms. Rotation about a vertical axis produces smaller convection cells with diminished heat fluxes and considerable vorticity. When the rotation axis is tilted from the vertical to represent tropical latitudes, the convection cells become elongated in a N-S direction. Imposed flows with constant vertical shear produce convective rolls aligned with the mean flow. When the rotation vector is tilted from the vertical, the competing effects due to rotation and shear can stabilize the convective motions.

Hathaway, D. H.↗
NASA NTRS2018

The Turbolift: Linear Sled Hybrid Artificial Gravity Concept

Future crewed space exploration missions into deep space will require enhanced countermeasure technologies to ensure astronaut health. One such hazard is extended exposure to reduced gravity levels (i.e., microgravity, lunar gravity, or Martian gravity). Reduced gravity negatively impacts many physiological systems, leading to hydrostatic intolerance, musculoskeletal atrophy, sensorimotor impairment, bone demineralization, cardiovascular deconditioning, and visual alterations. Various countermeasures have been employed for mitigating these effects, such as exercise, pharmaceuticals, diet, and fluid loading. However, these approaches treat individual symptoms, such that each physiological system is addressed with typically one countermeasure. An alternative to this approach is artificial gravity (AG), which promises to be a holistic, comprehensive countermeasure. The traditional approach to creating AG is through centrifugation. However, centrifugation is not a "pure" form of AG and typically includes the drawbacks of Coriolis forces, gravity gradients, and vestibular cross-coupled illusions.As an alternative, we have proposed a Linear Sled Hybrid (LSH) AG system to mitigate astronauts' physiological deconditioning. This system functions by applying pure linear acceleration to produce footward loading. There is a half rotation (180_) to reorient the rider between acceleration and deceleration phases, such that the loading remains footward, as when standing on Earth. The rotation also provides some footward acceleration to the lower body through centripetal acceleration; hence the "hybrid" aspect of the design. At the end of the deceleration, the rider than accelerates back in the opposite direction and the sequence repeats.This proposed system could be integrated with future crewed space vehicles in a variety of manners.

Gruber, Jason↗
NASA NTRS2003

Use of GTE, Mozaic, Sonex, and UARS-MLS Data in Understanding Tropospheric Processes Critical to Model Development

During the first year we focused on the analysis of data collected on over 7600 commercial aircraft flights (the MOZAIC program). The aim was to further our understanding of the fundamental dynamical processes that drive mesoscale phenomena in the upper troposphere and lower stratosphere, and their effects on the advection of passive scalars. Through these studies we made the following findings. 2001]: We derived the Kolmogorov equation for the third-order velocity structure function on an f-plane. We showed how the sign of the function yields the direction of the energy cascade. The remarkable linearity of the measured off diagonal third-order structure function was studied. We suggested that the Coriolis term, which appears explicitly in this equation, may be crucial in understanding the observed kinetic energy spectra at scales larger than 100 km, instead of the nonlinear advection term as previously assumed. Also, we showed that decreases with latitude for mid- to high-latitudes, and tabulated the values. Ozone concentration structure functions were calculated by restricting the data points to approximately isentropic pairings. In this way we were able to make comparisons with scalar advection theories. We found that, at even the largest scales, there was no evidence for the simple scaling predicted for smooth advection/diffusion.

Newell, Reginald E.↗
NASA NTRS1979

The effect of cumulus friction on the simulation of the January Hadley Circulation by the GLAS model of the general circulation

A method of parameterizing the vertical mixing of horizontal momentum by cumulus convection was added to the GLAS model of the general circulation of the tropics. Addition of the cumulus friction term strengthened the winter Hadley circulation and smoothed the mean meridional wind field, with a slight increase in the eddy kinetic energy. The results showed that the intensity of the meridional circulation is regulated by the atmosphere's angular momentum budget, changes in the zonally-averaged Coriolis force correlate with the new cumulus friction term, and the intensification of Hadley circulation is a response of the mean meridional flow field to the downward cumulus field of relative angular momentum in the winter hemisphere.

Helfand, H. M.↗
NASA NTRS1974

Cyclonic disturbances and their consequences in the thermosphere

We draw attention to the possible existence of cyclonic type of disturbances in the thermosphere which are created by localized energy sources in the vicinity of the nightside (and possibly the dayside) auroral oval. Due to the Coriolis force and the character of F-region ion motions, cyclonic disturbance cells of limited extent (3000 to 5000 km) may appear in conjunction with auroral substorms or more prolonged geomagnetic activity. Owing to prevailing thermospheric winds, these disturbances can be expected to drift equatorwards to midlatitude regions. The disturbance zone can be characterized in terms of a cyclonic wind pattern and significant changes in thermospheric neutral gas composition. This latter effect results in decreased plasma densities in the F-region for the lifetime of the disturbance.

Banks, P. M.↗
NASA NTRS1993

Phenytoin as a countermeasure for motion sickness in NASA maritime operations

Seasickness is the most prevalent form of motion sickness and is an operational problem during Space Shuttle Solid-fueled Rocket Booster (SRB) retrieval. Phenytoin has been shown to protect against motion sickness induced by Coriolis stress. We exposed SRB recovery personnel to off-vertical rotation and sea motion after phenytoin or placebo. Phenytoin blood levels of at least 9 micrograms/ml were protective against motion sickness at sea. No change in susceptibility to nitrogen narcosis was seen in divers in chamber tests at 460 KPa. Phenytoin was used during the performance of critical and hazardous tasks during training and actual SRB recovery operations. Phenytoin is an effective operational countermeasure for motion sickness for selected SRB crew members.

Woodard, Daniel↗
NASA NTRS1986

Nonlinear interactions between convection, rotation and flows with vertical shear

The effects of a mean flow with vertical shear on the convective motions in a rotating layer are examined using a three-dimensional and time-dependent numerical model. In the absence of rotation, the convective motions are shown to be dominated by the shear flow when the Richardson number becomes greater than about -1.0. Both heat and momentum are carried down their respective gradients. For rotating cases with vertical rotation vectors, the Coriolis force turns the flow induced by the convection to produce a more complicated shear that changes direction with height. For rotating cases with tilted rotation vectors, the results depend on the direction of the shear. When the imposed flow is in the opposite direction, the convection motions are less energetic and are even suppressed entirely when the shear is strong. When the imposed flow is in the same direction, as that produced by the rotation, the convective motions are enhanced and a countergradient flux of momentum can be produced.

Hathaway, D. H.↗
NASA NTRS2020

Exploring the Limits of the Data-Model-Theory Synergy: “Hot” MW Transitions for Rovibrational IR Studies

In order to further improve the accuracy of rovibrational IR line lists generated from the “Best Theory +Reliable High-resolution Experiment” (BTRHE) strategy from 0.01-0.05 cm-1, or 300-1500 MHz, to ~10 MHz, we explore the current limits of the Data-Model-Theory synergy by examining the accuracy and consistency of existing data, then propose that “hot” bands in microwave (MW) spectra is the solution we need for future enhancements. The Ames SO2 J=0-20 rovibrational energy levels computed on the semi-empirically refined Ames-2 potential energy surface (PES) are fit to the Effective Hamiltonian (EH) model regularly used in the experimental infrared (IR) analysis for SO2 isotopologues. In the fitted EH(Ames) model, the rotational constants A/B/C and all 5 quartic centrifugal distortion constants display clear, systematic, and consistent patterns along the vibrational state energy or quanta. Such consistent patterns may facilitate the vibrational assignments for MW hot bands and extract more information from high temperature MW spectra. Some EH(Expt) analyses were carried out with the lowest order Coriolis Coupling term, C1. Their constants should not be directly compared with other EH(Expt) and EH(Ames) results. After excluding them, our  = EH(Ames)- EH(Expt) analyses for 5 isotopologues (626, 636, 646, 628 and 828) indicates some loss of accuracy and consistency starting from vibrational states as low as 22 or 1000 cm-1. Some EH parameters, e.g. K, may have relative deviations as large as 50-100% and totally lose any recognizable patterns. This simply means that current EH(Expt) models do not have the system-wide consistency we need to further refine the EH(Ames) and Ames rovibrational IR line lists. A large part of such defects are probably inherited from the limited precision of experimental line positions, i.e. 1E-3 ~ 1E-4 cm-1, or 3-30 MHz. This is confirmed in a series of truncation tests using the Ames data. Although the EH(Ames) consistency may help identify unreliable rovibrational EH(Expt) parameters, and make reliable predictions for minor isotopologues and unobserved vibrational bands, we believe only the highly accurate “hot” MW transitions can provide real enhancements for EH(Expt) accuracy and consistency. “Hot” MW spectra should play a more significant role in the future synergy of Data, Model, and Theory in the field of rovibrational IR studies.

Xinchuan Huang↗
NASA NTRS1991

Enhanced winds and tidal streams in massive X-ray binaries

The tidal effects created by the presence of a compact companion are expected to induce a stream of enhanced wind from the early-type primary star in massive X-ray binary systems. In this paper, two-dimensional gasdynamical simulations of such streams are presented. It is found that the wind enhancement is a sensitive function of the binary separation, and develops into a tidal stream as the primary approaches its critical surface. For typical system parameters, the Coriolis force deflects the stream sufficiently that it does not impact directly on the compact companion but passes behind it. The density in the stream can reach values of 20-30 times the ambient wind density, leading to strong attenuation of the X-ray flux that passes through the tidal stream, providing a possible explanation of the enhanced absorption events seen at later phases in the X-ray observations of massive X-ray binary systems such as Vela X-1. In contrast to the time-variable accretion wake, the tidal stream is relatively stationary, producing absorption features that should remain fixed from orbit to orbit. For systems with a strong tidal stream, the large asymmetry in the accreting wind results in the accretion of angular momentum of constant sign, as opposed to systems without streams, where the sign of the accreted angular momentum can change.

Blondin, John M.↗
NASA NTRS1992

Mixed convective-dynamic roll vortices and their effects on initial wind and temperature profiles

A new nonlinear 14-coefficient spectral model of two-dimensional shallow Boussinesq flow is developed and used to investigate the onset and development of both dynamically and convectively forced boundary-layer rolls. The model is developed to accept arbitrary basic-state wind profiles as dynamic forcing, using an Ekman profile to provide a means for easy comparison with other studies. The results are qualitatively compared with those of previous theoretical and observational investigations. The rolls are shown to significantly alter the initial wind profile in the sense found by Faller and Kaylor (1967) and Brown (1970), but via a mechanism independent of the Coriolis force.

Haack, Tracy↗
NASA NTRS1993

Computation of incompressible viscous flows through turbopump components

Flow through pump components, such as an inducer and an impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. the equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use a one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside a generic rocket engine pump inducer, a fuel pump impeller, and SSME high pressure fuel turbopump impeller. Numerical results of inducer flow are compared with experimental measurements. In the fuel pump impeller, the effect of downstream boundary conditions is investigated. Flow analyses at 80 percent, 100 percent, and 120 percent of design conditions are presented.

Kiris, Cetin↗
NASA NTRS1993

Incompressible Navier-Stokes Calculations in Pump Flows

Flow through pump components, such as the SSME-HPFTP Impeller and an advanced rocket pump impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside an 11-inch SSME High Pressure Fuel Turbopump impeller, and an advanced rocket pump impeller. Numerical results of SSME-HPFTP impeller flow are compared with experimental measurements. In the advanced pump impeller, the effects of exit and shroud cavities are investigated. Flow analyses at design conditions will be presented.

Kiris, Cetin↗
NASA NTRS1989

Computation of three dimensional turbulent boundary layers in internal flows, including turbomachinery rotor blades

A method is developed for predicting three-dimensional turbulent boundary layers occurring in internal flows, including rotor blades of turbomachinery. These boundary layers are complex, turbulent, and are subject to Coriolis and centrifugal forces. The algebraic Reynolds stress model (ARSM) developed in this paper satisfies the realizability conditions exactly and captures the changes in turbulenet structure arising from curvature and rotation. The prediction of pressure driven secondary flow agrees well with the data and all the three turbulent models (k-e, algebraic eddy viscosity, and ARSM) show the same level of agreement. The prediction of boundary layer on rotor blades shows much better agreement with the ARSM. It is essential to employ the higher order models to capture the effects of rotation and curvature and three-dimensional boundary layers in turbomachinery.

Zhang, J.↗
NASA NTRS1993

Lee waves: Benign and malignant

The flow of an incompressible fluid over an obstacle will produce an oscillation in which buoyancy is the restoring force, called a gravity wave. For disturbances of this scale, the atmosphere may be treated as dynamically incompressible, even though there exists a mean static upward density gradient. Even in the linear approximation - i.e., for small disturbances - this model explains a great many of the flow phenomena observed in the lee of mountains. However, nonlinearities do arise importantly, in three ways: (1) through amplification due to the decrease of mean density with height; (2) through the large (scaled) size of the obstacle, such as a mountain range; and (3) from dynamically singular levels in the fluid field. These effects produce a complicated array of phenomena - large departure of the streamlines from their equilibrium levels, high winds, generation of small scales, turbulence, etc. - that present hazards to aircraft and to lee surface areas. The nonlinear disturbances also interact with the larger-scale flow in such a manner as to impact global weather forecasts and the climatological momentum balance. If there is no dynamic barrier, these waves can penetrate vertically into the middle atmosphere (30-100 km), where recent observations show them to be of a length scale that must involve the coriolis force in any modeling. At these altitudes, the amplitude of the waves is very large, and the phenomena associated with these wave dynamics are being studied with a view to their potential impact on high performance aircraft, including the projected National Aerospace Plane (NASP). The presentation shows the results of analysis and of state-of-the-art numerical simulations, validated where possible by observational data, and illustrated with photographs from nature.

Wurtele, M. G.↗
NASA NTRS1992

Materials processing in a centrifuge - Numerical modeling of macrogravity effects

The fluid mechanics associated with crystal growth processes on a centrifuge is investigated. A simple scaling analysis is used to examine the relative magnitudes of the forces acting on the system and good agreement is obtained with previous studies. A two-dimensional model of crystal growth on a centrifuge is proposed and calculations are undertaken to help in understanding the fundamental transport processes within the crystal growth cell. Results from three-dimensional calculations of actual centrifuge-based crystal growth systems are presented both for the thermodynamically stable and unstable configurations. The calculations show the existence of flow bifurcations in certain configurations but not in all instances. The numerical simulations also show that the centrifugal force is the dominant stabilizing force on fluid convection in the stable configuration. The stabilizing influence of the Coriolis force is found to be only secondary in nature. No significant impact of gravity gradient is found in the calculations. Simulations of unstable configurations show that the Coriolis force has a stabilizing influence on fluid motion by delaying the onset of unsteady convection. Detailed flow and thermal field characteristics are presented for all the different cases that are simulated.

Ramachandran, N.↗
NASA NTRS1998

The relative roles of the otolith organs and semicircular canals in producing space motion sickness

Inflight and post-landing "immunity" to the "coriolis sickness susceptibility test", observed during the Skylab M131 experiment, suggests that the otolith organs play a major role in space motion sickness (SMS). This view is supported by the report that ocular counter-torsion asymmetries correlate with SMS incidence and severity. Further data indicate that sensory-motor adaptation to microgravity includes a process whereby central interpretation of otolith signals is biased from "tilt" toward translation. However, unexpected responses to linear acceleration suggest the importance of graviceptors distributed throughout the body in addition to the vestibular otolith organs. Research is needed to assess distributed graviceptor effects.

Non-NASA Center↗
NASA NTRS1990

Computation and turbulence modeling for three-dimensional boundary layers including turbomachinery rotor flows

A method is developed for predicting the behavior of three-dimensional, turbulent boundary layers occurring in internal flows, including those on turbomachinery rotor blades. These boundary layers are complex, turbulent, and subject to Coriolis and centrifugal forces. The major thrust of this paper is the development and use of an algebraic Reynolds stress model (ARSM) that captures the changes in turbulent flow structure arising from curvature, rotation, and three dimensionality. The prediction of pressure-driven secondary flow agrees well with the measured data, and all three turbulence models (k-epsilon, algebraic eddy viscosity, and ARSM) show the same level of agreement. The prediction of boundary-layer development on rotor blades shows much better agreement with measurements with the ARSM. It is essential to employ higher-order turbulence models to capture the effects of rotation, curvature, and three dimensionality on boundary layers in turbomachinery.

Zhang, J.↗