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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The local dispersion relation for magneto-atmospheric waves

The local dispersion relation for magneto-atmospheric waves is discussed in terms of the linearized theory of waves in a plane-stratified, inviscid, perfectly conducting atmosphere under uniform gravity. The normally used local dispersion relation is demonstrated to not be unique, depending instead on the order of derivation from the fundamental first-order perturbation equations of continuity, momentum, energy, and induction. Furthermore, it is shown that the local dispersion relation predicts that the cutoff frequency decreases with increasing magnetic field strength, while the WKB approximation method projects an increase in the cutoff frequency with increasing magnetic field strength. A new form of the local dispersion relation is developed, and consideration is given to the special case of a global dispersion relation in conditions of an isothermal atmosphere with a horizontal magnetic field.

Thomas, J. H.↗
NASA NTRS1983

A study of non-unique solutions of the two-dimensional boundary layer equations at laminar separation and reattachment points

Nonunique laminar boundary layer equation solutions in direct problem calculations are identified for the case of accelerating flow. As a separation or reattachment point is approached, the multiple solutions approach each other and become identical. The computer code used to generate these results was developed for the solution of compressible, laminar or turbulent boundary layer, and free wake problems, in either direct or inverse mode. Similarity solutions in either a primitive variable or a stream function form are possible, and the resulting equations are solved by means of a modified Keller's Box scheme in which the energy equation and turbulence modeling equations are solved simultaneously with the continuity and momentum equations. Examples illustrating the nature of the solutions at the separation and reattachment points are presented.

Drela, M.↗
NASA NTRS1984

The mechanisms of flame holding in the wake of a bluff body

The flame holding mechanism for lean methane and lean propane air flames is examined under conditions where the recirculation zone is absent. The holding process is studied in detail in an attempt to determine the mechanism of flame holding and also the conditions where this mechanism is viable and when it fails and blow off occurs. Inverted flames held in the wake of a flat strip are studied. The velocity flow field is determined using a Laser Doppler Velocimetry technique. Equation of continuity is used to calculate the flame temperature from the change in area of flow streamlines before and after the flame. For methane air flame the controlling factor for blow off is incomplete reaction due to higher blowing rate leading to reduced residence time in the reaction zone.

Strehlow, R. A.↗
NASA NTRS1985

The mechanisms of flame holding in the wake of a bluff body

The flame holding mechanism for lean methane- and lean propane-air flames is examined under conditions where the recirculation zone is absent. The main objective of this work is to study the holding process in detail in an attempt to determine the mechanism of flame holding and also the conditions where this mechanism is viable and when it fails and blow-off occurs. Inverted flames held in the wake of a flat strip were studied. Experiments with different sizes of flame holders were performed. The velocity flow field was determined using a laser Doppler velocimetry technique. Equation of continuity was used to calculate the flame temperature from the change in area of flow streamlines before and after the flame. Observations of the inverted flame itself were obtained using schlieren and direct photography. Results show that there are different mechanisms operative at the time of blow-off for lean propane and methane flames. Blow-off or extinction occurs for lean propane-air flame in spite of the reaction going to completion and the disparity between the heat loss and the gain in mass diffusion in the reaction zone i.e., Le 1.0 causes the flame to blow-off. For methane-air flame the controlling factor or blow-off is incomplete reaction due to higher blowing rate leading to reduced residence time in the reaction zone.

Strehlow, R. A.↗
NASA NTRS1984

Development of a three-phrase combustion code for modeling liquid rocket engines

A two-dimensional/axisymmetric program for the simulation of three-phase reactive flows is presented. The three phases are: a multiple-species gaseous phase, a single-species liquid phase, and a particulate droplet phase. The liquid and gaseous phases are described with continuous Eulerian equations, while the droplets are described in a discrete Lagrangian fashion. The three phases are fully coupled together. An atomization model, a multireaction chemical kinetics model, and a subgrid scale turbulence model completes the description of a general liquid/gas bipropellant combustion process. The code development criteria and qualitative features are highlighted.

Liang, P. Y.↗
NASA NTRS1986

Heat and mass transfer in a dissociated laminar boundary layer of air with consideration of the finite rate of chemical reaction

A numerical investigation of heat and mass transfer in a dissociated laminar boundary layer of air on an isothermal flat plate is carried out for different degrees of cooling of the wall. A finite-difference chemical model is used to study elementary reactions involving NO2 and N2O. The analysis is based on equations of continuity, momentum, energy, conservation and state for the two-dimensional viscous flow of a reacting multicomponent mixtures. Attention is given to the effects of both catalyticity and noncatalyticity of the wall.

Oyegbesan, A. O.↗
NASA NTRS1985

The photochemistry of the early atmosphere

The composition of the earth's present atmosphere is described. The formation of the earth from the coalescence and accretion of the refractory elements of the solar nebula is examined. Two possible compositions of the prebiological paleoatmosphere, which are a reducing atmosphere of CH4, NH3, and H2 or a mildly reducing atmosphere of H2O, CO2, and N2, and their photochemistry are analyzed. General photochemical and chemical processes are reviewed. The use of the coupled continuity-transport equation to calculate the vertical distribution of each species is discussed. A study of the photochemical process of CH4 and NH3 reveals that the reducing atmosphere could not possibly exist. An analysis of the photochemistry and chemistry of the H2O, CO2, and N2 atmosphere reveals that the photodissociation of H2O and CO2 results in a prebiotic source of O2, H2CO, and HCN, which are the components for the evolution of photosynthetic organisms and a strongly oxidizing atmosphere. The reactions which produce O2 and H2CO from H2O and CO2, and the relation between H2O and CO2 concentrations and O2 levels are investigated. The formation of O3 photochemically from O2 is explained.

Levine, J. S.↗
NASA NTRS1986

Helium and minor ions in the corona and solar wind - Dynamics and charge states

A theoretical model of the acceleration region of the solar wind with major species (p, alpha, e) and minor ions (e.g., He-3, C, O, Mg, Si) is presented. Observed n(e)-profiles and the equations of continuity and momentum are used to calculate profiles of T, n, and u for all species, as well as charge states of minor ions. The disagreement of the results of a pure p-e model with observations is discussed in some detail, and it is shown that a model consistent with observations both in the corona and at 1 AU requires a finite abundance of He(2+). This model predicts a strong enhancement of He/H in the lower corona. The results for the frozen-in charge states in the p-alpha-e model are in agreement with measurements in the low speed solar wind, especially for the well determined pair O(6+)/O(7+). Finally, a model for a coronal hole is investigated and it is found that wave pressure is necessary to model successfully the observed solar wind speeds and abundances. Although various simplifying assumptions had to be introduced, care was taken to ensure that the model remains physically consistent, i.e., that the same physics is used for the major species as well as the minor ions.

Buergi, A.↗
NASA NTRS1990

Effects of turbulence mixing, variable properties, and vaporization on spray droplet combustion

Combustion of liquid fuels in the form of spray droplets is simulated numerically. Various vaporization models are examined as to their performance in finite element calculations involving a turbulent flow field. The Eulerian coordinate for the gas and Lagrangian coordinate for the liquid spray droplets are coupled through source terms being updated in the equations of continuity, momentum, and energy. The k-epsilon and modified eddy breakup models are used for simulating turbulent spray combustion flow field. Numerical results for the droplet trajectories, droplet heating, recirculation characteristics, and effects of evaporation models are evaluated. It is also shown that the finite element method is advantageous in dealing with complex geometries, complex boundary conditions, adaptive unstructured grids.

Kim, Y. M.↗
NASA NTRS1989

Six-degree-of-freedom aircraft simulation with mixed-data structure using the applied dynamics simulation language, ADSIM

A realistic simulation of an aircraft in the flight using the AD 100 digital computer is presented. The implementation of three model features is specifically discussed: (1) a large aerodynamic data base (130,00 function values) which is evaluated using function interpolation to obtain the aerodynamic coefficients; (2) an option to trim the aircraft in longitudinal flight; and (3) a flight control system which includes a digital controller. Since the model includes a digital controller the simulation implements not only continuous time equations but also discrete time equations, thus the model has a mixed-data structure.

Savaglio, Clare↗
NASA NTRS1990

A time-dependent dusty gas dynamic model of axisymmetric cometary jets

The present time-dependent, axisymmetric dusty gas dynamical model of inner cometary atmospheres solves the coupled and time-dependent equations of continuity, momentum, and energy for a gas-dust mixture between the surface of the nucleus and 100 km, using an axisymmetric 40 x 40 grid structure. A novel numerical method employing a second-order accurate Godunov-type scheme with dimensional splitting is used to solve the time-dependent pde system. It is established that a subsolar dust spike not predicted by previous calculations is generated by narrow axisymmetric jets, together with a jet cone whose opening angle depends on the jet length.

Korosmezey, A.↗
NASA NTRS1993

The 3-D CFD modeling of gas turbine combustor-integral bleed flow interaction

An advanced 3-D Computational Fluid Dynamics (CFD) model was developed to analyze the flow interaction between a gas turbine combustor and an integral bleed plenum. In this model, the elliptic governing equations of continuity, momentum and the k-e turbulence model were solved on a boundary-fitted, curvilinear, orthogonal grid system. The model was first validated against test data from public literature and then applied to a gas turbine combustor with integral bleed. The model predictions agreed well with data from combustor rig testing. The model predictions also indicated strong flow interaction between the combustor and the integral bleed. Integral bleed flow distribution was found to have a great effect on the pressure distribution around the gas turbine combustor.

Chen, D. Y.↗
NASA NTRS1994

Linear and nonlinear dynamic analysis of redundant load path bearingless rotor systems

The goal of this research is to develop the transfer matrix method to treat nonlinear autonomous boundary value problems with multiple branches. The application is the complete nonlinear aeroelastic analysis of multiple-branched rotor blades. Once the development is complete, it can be incorporated into the existing transfer matrix analyses. There are several difficulties to be overcome in reaching this objective. The conventional transfer matrix method is limited in that it is applicable only to linear branch chain-like structures, but consideration of multiple branch modeling is important for bearingless rotors. Also, hingeless and bearingless rotor blade dynamic characteristics (particularly their aeroelasticity problems) are inherently nonlinear. The nonlinear equations of motion and the multiple-branched boundary value problem are treated together using a direct transfer matrix method. First, the formulation is applied to a nonlinear single-branch blade to validate the nonlinear portion of the formulation. The nonlinear system of equations is iteratively solved using a form of Newton-Raphson iteration scheme developed for differential equations of continuous systems. The formulation is then applied to determine the nonlinear steady state trim and aeroelastic stability of a rotor blade in hover with two branches at the root. A comprehensive computer program is developed and is used to obtain numerical results for the (1) free vibration, (2) nonlinearly deformed steady state, (3) free vibration about the nonlinearly deformed steady state, and (4) aeroelastic stability tasks. The numerical results obtained by the present method agree with results from other methods.

Murthy, V. R.↗
NASA NTRS2002

Geostrophic balance with a full Coriolis Force: implications for low latitutde studies

In its standard form, geostrophic balance uses a partial representation of the Coriolis force. The resulting formation has a singularity at the equator, and violates mass and momentum conservation. When the horizontal projection of the planetary rotation vector is considered, the singularity at the equator disappears, continuity can be preserved, and quasigeostrophy can be formulated at planetary scale.

balance atmosphere geostrophy remote sensing wind↗
NASA NTRS2010

Turbofan Volume Dynamics Model for Investigations of Aero-Propulso-Servo-Elastic Effects in a Supersonic Commercial Transport

A turbofan simulation has been developed for use in aero-propulso-servo-elastic coupling studies, on supersonic vehicles. A one-dimensional lumped volume approach is used whereby each component (fan, high-pressure compressor, combustor, etc.) is represented as a single volume using characteristic performance maps and conservation equations for continuity, momentum and energy. The simulation is developed in the MATLAB/SIMULINK (The MathWorks, Inc.) environment in order to facilitate controls development, and ease of integration with a future aero-servo-elastic vehicle model being developed at NASA Langley. The complete simulation demonstrated steady state results that closely match a proposed engine suitable for a supersonic business jet at the cruise condition. Preliminary investigation of the transient simulation revealed expected trends for fuel flow disturbances as well as upstream pressure disturbances. A framework for system identification enables development of linear models for controller design. Utilizing this framework, a transfer function modeling an upstream pressure disturbance s impacts on the engine speed is developed as an illustrative case of the system identification. This work will eventually enable an overall vehicle aero-propulso-servo-elastic model

Connolly, Joseph W.↗
NASA NTRS2012

Dual-Doppler Feasibility Study

When two or more Doppler weather radar systems are monitoring the same region, the Doppler velocities can be combined to form a three-dimensional (3-D) wind vector field thus providing for a more intuitive analysis of the wind field. A real-time display of the 3-D winds can assist forecasters in predicting the onset of convection and severe weather. The data can also be used to initialize local numerical weather prediction models. Two operational Doppler Radar systems are in the vicinity of Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS); these systems are operated by the 45th Space Wing (45 SW) and the National Weather Service Melbourne, Fla. (NWS MLB). Dual-Doppler applications were considered by the 45 SW in choosing the site for the new radar. Accordingly, the 45th Weather Squadron (45 WS), NWS MLB and the National Aeronautics and Space Administration tasked the Applied Meteorology Unit (AMU) to investigate the feasibility of establishing dual-Doppler capability using the two existing systems. This study investigated technical, hardware, and software requirements necessary to enable the establishment of a dual-Doppler capability. Review of the available literature pertaining to the dual-Doppler technique and consultation with experts revealed that the physical locations and resulting beam crossing angles of the 45 SW and NWS MLB radars make them ideally suited for a dual-Doppler capability. The dual-Doppler equations were derived to facilitate complete understanding of dual-Doppler synthesis; to determine the technical information requirements; and to determine the components of wind velocity from the equation of continuity and radial velocity data collected by the two Doppler radars. Analysis confirmed the suitability of the existing systems to provide the desired capability. In addition, it is possible that both 45 SW radar data and Terminal Doppler Weather Radar data from Orlando International Airport could be used to alleviate any radar geometry issues at the NWS MLB radar, such as the "cone of silence" or beam blockage. In the event of a radar outage at one of the sites, the multi-radar algorithms would provide continuing coverage of the area through use of the data from the remaining operational radar sites. There are several options to collect, edit, synthesize and display dual-Doppler data sets. These options include commercial packages available for purchase and a variety of freeware packages available from the National Center for Atmospheric Research (NCAR) for processing raw radar data. However, evaluation of the freeware packages revealed that they do not have sufficient documentation and configuration control to be certified for 45 SW use. Additionally, a TI data line must be installed/leased from the NWS MLB office and CCAFS to enable the receipt of NWS MLB raw radar data to use in the dual-Doppler synthesis. Integration of the TI data line into the Eastern Range infrastructure that will meet the security requirements necessary for 45 SW use is time-consuming and costly. Overall evaluation indicates that establishment of the dual-Doppler capability using the existing operational radar systems is desirable and feasible with no technical concerns. Installation of such a system represents a significant enhancement to forecasting capabilities at the 45 WS and at NWS MLB. However, data security and cost considerations must be evaluated in light of current budgetary constraints. In any case, gaining the dual-Doppler capability will provide opportunities for better visualization of the wind field and better forecasting of the onset of convection and severe weather events to support space launch operations at KSC and CCAFS.

Huddleston, Lisa L.↗
NASA NTRS1994

Pseudomaster equation for the no-count process in a continuous photodetection

The detection of cavity radiation with the detector placed outside the cavity is studied. Each leaked photon has a certain probability of propagating away without being detected. It is viewed as a continuous quantum measurement in which the density matrix is continuously revised according to the readout of the detector. The concept of pseudomaster equation for the no-count process is introduced; its solution leads to the discovery of the superoperator for the same process. It has the potential to become the key equation for continuous measurement process.

Lee, Ching-Tsung↗