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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Thermal environment around the Space Shuttle with hot-gas jets for ice suppression

To prevent prelaunch ice formation on the external tank of the Space Shuttle, the final selected approach is to heat the surrounding air with vertical hot-gas jets located at the launch pad. This approach was considerably more cost-effective than other ice suppression methods considered, although its feasibility was not easily discernible due to the complex flowfield interactions. This paper describes how the use of vertical jets was first evaluated with the aid of a computational fluid dynamics (CFD) technique. An existing general-purpose CFD program (PHOENICS) was used to predict the thermal environment around the Shuttle under various jet configurations and wind conditions. The program accounts for effects of buoyancy, turbulence, and structural obstructions in the flowfield. The computed results showed physically plausible and consistent trends. The wind wake effects were found to be significant, and normally resulted in higher temperatures on the leeward side of the tank. High wind conditions were found to be more severe than calm wind conditions. The use of four jets with two different temperatures was identified as a promising option in which the air temperatures were raised sufficiently to prevent ice formation on the external tank, without excessive increase in Orbiter surface temperature. The use of the numerical model also facilitated the selection of test configurations and a test matrix for verifying the approach. Selected results of an experimental verification (by using a 2 percent scale model in a wind tunnel) are also presented.

Singhal, A. K.↗
NASA NTRS1992

Studies of turbulent shear flows and their control

The intent of the original proposal and the work carried out under the grant was to explore the instabilities of turbulent free shear flows of an incompressible fluid. The purpose for doing so was that coherent instabilities are susceptible to control via upstream forcing and because at sufficient finite amplitudes, the coherent modes enter into nonlinear interactions with the mean motion and thus, through such nonlinear interactions, the control of mixing and of mean flow spreading can be effected through the control of the coherent structures.

Liu, Joseph T. C.↗
NASA NTRS1995

Tracking a turbulent spot in an immersive environment

We describe an interactive, immersive 3D system called Tracktur, which allows a viewer to track the development of a turbulent flow. Tracktur displays time-varying vortex structures extracted from a numerical flow simulation. The user navigates the space and probes the data within a windy 3D landscape. In order to sustain a constant frame rate, we enforce a fixed polygon budget on the geometry. We supplement the interactive system with interactive, hypertext documentation available on the World Wide Web. In actual use by a fluid dynamicist, the system has yielded new insights into the transition to turbulence in a laminar flow.

Banks, David C.↗
NASA NTRS1993

A new approach to the study of the turbulence layer

Turbulent thermal convection is of considerable importance in fluid dynamical transport phenomena occurring, for example, in the planetary boundary layer of the Earth, the interiors of stars, and accretion disks. In particular, during a significant portion of the evolutionary phase of many stars having convectively unstable cores or outer envelopes, a substantial fraction of energy is transported from the central layers to the outer layers by thermal convection. Moreover, as much of the interior of a star is in highly turbulent motion, a complete theory of stellar structure and evolution requires the explicit consideration of turbulence in order to have expressions for the turbulent quantities arising in the stellar structure equations, and particularly, the turbulent fluxes that appear in the total flux conservation equation, such as the convective flux, kinetic energy flux, etc. A reliable quantification of these fluxes continues to present a challenge in astrophysical fluid dynamics, primarily because astrophysical turbulence is almost always fully-developed and nearly inviscid, and therefore governed by strong nonlinear interactions that distribute the energy among a very wide spectrum of eddies with scales ranging from the characteristic dimension of the flow to those sufficiently small to be affected by viscous dissipation. Furthermore, astrophysical flows are invariably compressible, anisotropic, and inhomogeneous, which requires the consideration of the dynamics of longitudinal modes and their interaction with the transverse modes, as well as complicated boundary conditions. In order to reach a compromise between analytical and numerical tractability and the basic physics of turbulent convection, we have constructed a model of stationary turbulent convection that yields various turbulence statistics, including the convective flux, that are required in stellar evolution models.

Levenson, Ruth A.↗
NASA NTRS1992

Role of shock dynamics in transonic flutter

A computational study of the influence of shock motion on flutter and divergence in transonic flow is presented. The numerical scheme models the entire fluid-structure system as a single continuum dynamics problem, by using a mixed Eulerian-Lagrangian formulation. No assumptions of small displacements are made, but the effect of viscosity is neglected. The results from this study indicate that the shock dynamics gives rise to limit cycles and highly nonlinear aeroelastic phenomena, such as weak divergence and flutter-divergence interactions. Although the shocks typically are destabilizing at the linear flutter boundary, they often have a strongly stabilizing effect for moderate-amplitude motions. The shocks are thus capable of quenching an emerging bending-torsion flutter motion and turning it into limit cycle flutter. The usefulness of classical flutter and divergence boundary diagrams is severely limited in transonic flow, because much of the global dynamic stability information is lost in such a presentation.

Bendiksen, Oddvar O.↗
NASA NTRS1987

A preliminary study of extended magnetic field structures in the ionosphere

Several plasma phenomena which are to be expected around a magnet in LEO were identified and analyzed qualitatively. The ASTROMAG cusp magnet will create an extended field whose strength drops to the ambient level over a scale length of approx. 15 m; the combined field has a complex topology with ring nulls and open and closed field lines. The entire configuration is moving through the partially ionized F-layer of the ionosphere at a speed slow compared to the local Alfven speed but fast compared to the ion sound speed. The ambient plasma crosses the extended field structure in a time short compared to the ion Larmor period yet long relative to the electron Larmor period. Thus, electrons behave as a magnetized fluid while ions move ballistically until reflected from higher fields near the cusp. Since the Debye length is short compared to the field scale length, an electrostatic shock-like structure forms to equilibrate the flows and achieve quasi-neutrality. The ambient plasma will be excluded from a cavity near the magnet. The size and nature of the strong interaction region in which the magnet significantly perturbs the ambient flow were determined by studying ion orbits numerically. Lecture viewgraphs summarizing these results are presented.

Sullivan, James D.↗
NASA NTRS2015

Structural-Thermal-Optical-Performance (STOP) Analysis

The presentation will be given at the 26th Annual Thermal Fluids Analysis Workshop (TFAWS 2015) hosted by the Goddard Spaceflight Center (GSFC) Thermal Engineering Branch (Code 545). A STOP analysis is a multidiscipline analysis, consisting of Structural, Thermal and Optical Performance Analyses, that is performed for all space flight instruments and satellites. This course will explain the different parts of performing this analysis. The student will learn how to effectively interact with each discipline in order to accurately obtain the system analysis results.

Optical↗
NASA NTRS1998

The bearable lightness of being: bones, muscles, and spaceflight

Bones and muscles support and move the body. Tendons link the two tissues and serve as a mechanism for transfer of forces from muscle to bone. These three tissues interact and respond to periods of activity or inactivity with appropriate alterations in structure and strength. There is substantial evidence that an environment devoid of mechanical stress on the skeleton (such as reduced gravitational forces during spaceflight, a "microgravity environment") produces direct effects on bone structure and function. There is little agreement concerning the biologic mechanisms for these atrophic changes. Changes in fluid balance and distribution coincident to spaceflight also affect muscles and bones by an unknown mechanism. Tendon-bone junctions are presumed to be spared from the effects of spaceflight. However, recent evidence from rodents suggests that spaceflight profoundly effects both the skeleton and the tendon-bone junctions. These effects include cortical bone resorption, which undermines the Sharpey's fibers that anchor the tendon to the bone matrix. The challenge to biomedical scientists is to devise methods for protecting spaceflight crews from these atrophic changes; such protection would allow for longer and more extensive spaceflights.

manned↗
NASA NTRS1993

Numerical simulation of steady and unsteady viscous flow in turbomachinery using pressure based algorithm

The objective of this research is to simulate steady and unsteady viscous flows, including rotor/stator interaction and tip clearance effects in turbomachinery. The numerical formulation for steady flow developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbomachinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation, and is applicable to both viscous and inviscid flows. The values of these artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure of tip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities of leakage mass flow, vortex strength, losses, dominant leakage flow regions and the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately. The above numerical formulation was modified to incorporate time accurate solutions. An inner loop iteration scheme is used at each time step to account for the non-linear effects. The computation of unsteady flow through a flat plate cascade subjected to a transverse gust reveals that the choice of grid spacing and the amount of artificial dissipation is critical for accurate prediction of unsteady phenomena. The rotor-stator interaction problem is simulated by starting the computation upstream of the stator, and the upstream rotor wake is specified from the experimental data. The results show that the stator potential effects have appreciable influence on the upstream rotor wake. The predicted unsteady wake profiles are compared with the available experimental data and the agreement is good. The numerical results are interpreted to draw conclusions on the unsteady wake transport mechanism in the blade passage.

Lakshminarayana, B.↗
NASA NTRS1983

SPAR improved structure/fluid dynamic analysis capability

The capability of analyzing a coupled dynamic system of flowing fluid and elastic structure was added to the SPAR computer code. A method, developed and adopted for use in SPAR utilizes the existing assumed stress hybrid plan element in SPAR. An operational mode was incorporated in SPAR which provides the capability for analyzing the flaw of a two dimensional, incompressible, viscous fluid within rigid boundaries. Equations were developed to provide for the eventual analysis of the interaction of such fluids with an elastic solid.

Oden, J. T.↗
NASA NTRS1989

Calculations of inlet distortion induced compressor flow field instability

Calculations of the onset of flow instability are carried out for low-speed multistage axial compressors operating with asymmetric inlet flow. The modeling of the fluid dynamic interaction between the spoiled and unspoiled sectors of the compressor is the most important feature of the calculation procedure. The calculations show that annulus average slope of the compressor pressure rise characteristic equal to zero is a useful approximate stability criterion for situations where the dynamics of the compressor flow field do not couple strongly to the compression system or the structure of the imposed distortion is not similar to that of the eigenmodes of the flow in the compressor annulus. This criterion is employed to investigate the relationship between the present model and the 'parallel compressor' model. Calculations are also presented for cases when compressor and compressor system are closely coupled, and situations in which the compressor is subjected to a rotating distortion. These first-of-a-kind computations, and the accompanying description of the physical mechanisms, show that the stability of the flow in the compressor can be adversely affected if the temporal or spatial structure of the distortion is such that resonant type responses can be evoked either from the compressor or from compressor/compression system interactions.

Chue, R.↗
NASA NTRS1989

Group-kinetic theory and modeling of atmospheric turbulence

A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.

Tchen, C. M.↗
NASA NTRS1997

Turbine blade tip/outer airseal/platform flow analysis

The interaction between the main passage flow through a high pressure turbine and the secondary flows due to leakage through the wheelspace rim seals is reviewed. Various experimental and analytical studies of these interactions are outlined and a numerical investigation of the interaction between the main passage flow and a wheelspace cavity seal flow is described. The numerical investigation uses a structured grid method to study the overall interaction between the turbine stage components and the wheelspace seal flow, and an unstructured grid method to resolve the detailed flow features within the geometrically complex cavity seal. The numerical results agree with various observations from experimental studies under similar flow conditions. As the flow rate through the rim cavity seal is increased, the ingestion of fluid from the main passage flow into the rim seal area decreases rapidly. A small amount of main flow gas is ingested into the rim seal area, even at high seal flow rates.

Hah, C.↗
NASA NTRS1995

Mechanotransduction and the functional response of bone to mechanical strain

Mechanotransduction plays a crucial role in the physiology of many tissues including bone. Mechanical loading can inhibit bone resorption and increase bone formation in vivo. In bone, the process of mechanotransduction can be divided into four distinct steps: (1) mechanocoupling, (2) biochemical coupling, (3) transmission of signal, and (4) effector cell response. In mechanocoupling, mechanical loads in vivo cause deformations in bone that stretch bone cells within and lining the bone matrix and create fluid movement within the canaliculae of bone. Dynamic loading, which is associated with extracellular fluid flow and the creation of streaming potentials within bone, is most effective for stimulating new bone formation in vivo. Bone cells in vitro are stimulated to produce second messengers when exposed to fluid flow or mechanical stretch. In biochemical coupling, the possible mechanisms for the coupling of cell-level mechanical signals into intracellular biochemical signals include force transduction through the integrin-cytoskeleton-nuclear matrix structure, stretch-activated cation channels within the cell membrane, G protein-dependent pathways, and linkage between the cytoskeleton and the phospholipase C or phospholipase A pathways. The tight interaction of each of these pathways would suggest that the entire cell is a mechanosensor and there are many different pathways available for the transduction of a mechanical signal. In the transmission of signal, osteoblasts, osteocytes, and bone lining cells may act as sensors of mechanical signals and may communicate the signal through cell processes connected by gap junctions. These cells also produce paracrine factors that may signal osteoprogenitors to differentiate into osteoblasts and attach to the bone surface. Insulin-like growth factors and prostaglandins are possible candidates for intermediaries in signal transduction. In the effector cell response, the effects of mechanical loading are dependent upon the magnitude, duration, and rate of the applied load. Longer duration, lower amplitude loading has the same effect on bone formation as loads with short duration and high amplitude. Loading must be cyclic to stimulate new bone formation. Aging greatly reduces the osteogenic effects of mechanical loading in vivo. Also, some hormones may interact with local mechanical signals to change the sensitivity of the sensor or effector cells to mechanical load.

Non-NASA Center↗
NASA NTRS2011

Overview of the Helios Version 2.0 Computational Platform for Rotorcraft Simulations

This article summarizes the capabilities and development of the Helios version 2.0, or Shasta, software for rotary wing simulations. Specific capabilities enabled by Shasta include off-body adaptive mesh refinement and the ability to handle multiple interacting rotorcraft components such as the fuselage, rotors, flaps and stores. In addition, a new run-mode to handle maneuvering flight has been added. Fundamental changes of the Helios interfaces have been introduced to streamline the integration of these capabilities. Various modifications have also been carried out in the underlying modules for near-body solution, off-body solution, domain connectivity, rotor fluid structure interface and comprehensive analysis to accommodate these interfaces and to enhance operational robustness and efficiency. Results are presented to demonstrate the mesh adaptation features of the software for the NACA0015 wing, TRAM rotor in hover and the UH-60A in forward flight.

Sankaran, Venkateswaran↗
NASA NTRS2016

Cold Flow Propulsion Test Complex Pulse Testing

When the propellants in a liquid rocket engine burn, the rocket not only launches and moves in space, it causes forces that interact with the vehicle itself. When these interactions occur under specific conditions, the vehicle's structures and components can become unstable. One instability of primary concern is termed pogo (named after the movement of a pogo stick), in which the oscillations (cycling movements) cause large loads, or pressure, against the vehicle, tanks, feedlines, and engine. Marshall Space Flight Center (MSFC) has developed a unique test technology to understand and quantify the complex fluid movements and forces in a liquid rocket engine that contribute strongly to both engine and integrated vehicle performance and stability. This new test technology was established in the MSFC Cold Flow Propulsion Test Complex to allow injection and measurement of scaled propellant flows and measurement of the resulting forces at multiple locations throughout the engine.

McDougal, Kris↗
NASA NTRS2020

Formation and Topology of Foreshock Bubbles

We use global and local hybrid (kinetic ions and fluid electrons) simulations to investigate the conditions under which foreshock bubbles (FBs) form and how their topology changes with solar wind conditions. FBs form as a result of the interaction between solar wind discontinuities and backstreaming ion beams in the foreshock. They consist of an outer shock and its associated sheath plasma and a low density high temperature core with low magnetic field strength. The structure of FBs is determined by the angle between the interplanetary magnetic field and the normal to the solar wind discontinuity. We show that interaction of rotational discontinuities with the foreshock during small angles between the interplanetary magnetic field and discontinuity normal results in the formation of a nearly spherical bubble with a radius that scales with the width of the foreshock. As this angle increases, FBs become more elongated and eventually become nearly planar structures with dimensions that scale with the length of the foreshock. Despite this transformation, the signatures of FBs in spacecraft time series data remain the same in agreement with the observations. Global simulation results show that FBs form when the solar wind flow speed corresponds to high or intermediate Alfvén Mach numbers (approximately >7 MA). In general, this is tied to the relative speed between the solar wind and ion beams and drop in density of the back streaming ions.

Nick Omidi↗
NASA NTRSDate not supplied

Computational Evaluation of an OML-based Heat Exchanger Concept for HEATheR

Feasibility of outer mold line (OML) heat exchangers for electrified aircraft is computationally explored for three different aircraft concepts within The High-efficiency Electrified Aircraft Thermal Research (HEATheR) project. OML surface temperature limits were selected based on aluminum-alloy and carbon-fiber composite materials commonly used in transport aircraft. Heat flux distribution over the aircraft OML at the surface temperature limit was evaluated with computational fluid dynamics (CFD) analysis. The candidate OML locations and the size for the implementation of the OML-based heat exchanger is down-selected using this initial analysis and other considerations including the concern for structural integrity and proximity to heat-generating electrical components. The sensitivity of the heat transfer analysis to the computational grid, aircraft angle of attack, surface temperature, and the interaction of individual OML heat exchanger patches were investigated.

CAS↗