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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 NTRS1935

Calculations of the Effect of Wing Twist on the Air Forces Acting on a Monoplane Wing

A method is presented for calculating the aerodynamic forces on a moncylane wing, taking into account the elastic twisting of the wing due to these forces. The lift distribution along the span is calculated by the formulas of Amstutz as a function of the geometrical characteristics of the wing and of the twist at stations 60 and 90 percent of the semispan. The twist for a given lift distribution is calculated by means of influence lines. As a numerical example, the forces on a Swiss military D.2V airplane are calculated. Comparisons with the strip method and with the ordinary stress-analysis method are also given.

FORMULAS-LIFT DISTRIBUTION-AMSTUTZ↗
NASA NTRS1958

Comparison of Calculated and Experimental Temperatures and Coolant Pressure Losses for a Cascade of Small Air-Cooled Turbine Rotor Blades

Average spanwise blade temperatures and cooling-air pressure losses through a small (1.4-in, span, 0.7-in, chord) air-cooled turbine blade were calculated and are compared with experimental nonrotating cascade data. Two methods of calculating the blade spanwise metal temperature distributions are presented. The method which considered the effect of the length-to-diameter ratio of the coolant passage on the blade-to-coolant heat-transfer coefficient and assumed constant coolant properties based on the coolant bulk temperature gave the best agreement with experimental data. The agreement obtained was within 3 percent at the midspan and tip regions of the blade. At the root region of the blade, the agreement was within 3 percent for coolant flows within the turbulent flow regime and within 10 percent for coolant flows in the laminar regime. The calculated and measured cooling-air pressure losses through the blade agreed within 5 percent. Calculated spanwise blade temperatures for assumed turboprop engine operating conditions of 2000 F turbine-inlet gas temperature and flight conditions of 300 knots at a 30,000-foot altitude agreed well with those obtained by the extrapolation of correlated experimental data of a static cascade investigation of these blades.

Stepka, Francis S↗
NASA NTRS1954

Method for calculating the rolling and yawing moments due to rolling for unswept wings with or without flaps or ailerons by use of nonlinear section lift data

The methods of NACA reports 865 and 1090 have been applied to the calculation of the rolling-moment and yawing-moment coefficients due to rolling for unswept wings with or without flaps or ailerons. The methods are based on lifting-line theory and allow the use of nonlinear section lift data. The method presented in this report permits calculations to be made somewhat beyond maximum lift for wings having no twist or continuous twist and employing airfoil sections which do not display large discontinuities in the lift curves. Calculations can be made up to maximum lift for wings with discontinuous twist such as that produced by partial-span flaps or ailerons, or both. Two calculated examples are presented in simplified computing forms in order to illustrate the procedures involve.

Martina, Albert P↗
NASA NTRS1955

Calculated spanwise lift distributions, influence functions, and influence coefficients for unswept wings in subsonic flow

Spanwise lift distributions have been calculated for nineteen unswept wings with various aspect ratios and taper ratios and with a variety of angle-of-attack or twist distributions, including flap and aileron deflections, by means of the Weissinger method with eight control points on the semispan. Also calculated were aerodynamic influence coefficients which pertain to a certain definite set of stations along the span, and several methods are presented for calculating aerodynamic influence functions and coefficients for stations other than those stipulated. The information presented in this report can be used in the analysis of untwisted wings or wings with known twist distributions, as well as in aeroelastic calculations involving initially unknown twist distributions.

Diederich, Franklin W↗
NASA NTRS1994

Use of Navier-Stokes methods for the calculation of high-speed nozzle flow fields

Flows through three reference nozzles have been calculated to determine the capabilities and limitations of the widely used Navier-Stokes solver, PARC. The nozzles examined have similar dominant flow characteristics as those considered for supersonic transport programs. Flows from an inverted velocity profile (IVP) nozzle, an under expanded nozzle, and an ejector nozzle were examined. PARC calculations were obtained with its standard algebraic turbulence model, Thomas, and the two-equation turbulence model, Chien k-epsilon. The Thomas model was run with the default coefficient of mixing set at both 0.09 and a larger value of 0.13 to improve the mixing prediction. Calculations using the default value substantially underpredicted the mixing for all three flows. The calculations obtained with the higher mixing coefficient better predicted mixing in the IVP and underexpanded nozzle flows but adversely affected PARC's convergence characteristics for the IVP nozzle case. The ejector nozzle case did not converge with the Thomas model and the higher mixing coefficient. The Chien k-epsilon results were in better agreement with the experimental data overall than were those of the Thomas run with the default mixing coefficient, but the default boundary conditions for k and epsilon underestimated the levels of mixing near the nozzle exits.

Georgiadis, Nicholas J.↗
NASA NTRS1994

Use of the sampling theorem to speed up near-field physical optics scattering calculations

Physical optics scattering calculations performed on the DSN 34-m beam-waveguide antennas at Ka-band (32 GHz) require approximately 12 hr of central processing unit time on a Cray Y-MP2 computer. This is excessive in terms of resource utilization and turnaround time. Typically, the calculations involve five surfaces, and the calculations are done two surfaces at a time. The sampling theorem is used to reduce the number of current values that must be calculated over the second surface by performing a physical optics integration over the first surface. The additional number of current values required on the second surface by subsequent physical optics integrations is obtained by interpolation over the original current values. Time improvements on the order of a factor of 2 to 4 were obtained for typical scattering pairs.

Cramer, P. W.↗
NASA NTRS1995

Theoretical calculations of pressure broadening coefficients for H2O perturbed by hydrogen or helium gas

Halfwidths were calculated for H2O with H2 as a broadening gas and were estimated for He as the broadening species. The calculations used the model of Robert and Bonamy with parabolic trajectories and all relevant terms in the interaction potential. The calculations investigated the dependence of the halfwidth on the order of the atom-atom expansion, the rotational states, and the temperature in the range 200 to 400K. Finally, calculations were performed for many transitions of interest in the 5 micrometer window region of the spectrum. The resulting data will be supplied to Dr. R. Freedman for extracting accurate water mixing ratios from the analysis of the thermal channels for the Net Flux experiment on the Galileo probe.

Gamache, Robert R.↗
NASA NTRS1995

Calculation of three-dimensional (3-D) internal flow by means of the velocity-vorticity formulation on a staggered grid

A method has been developed to accurately compute the viscous flow in three-dimensional (3-D) enclosures. This method is the 3-D extension of a two-dimensional (2-D) method developed for the calculation of flow over airfoils. The 2-D method has been tested extensively and has been shown to accurately reproduce experimental results. As in the 2-D method, the 3-D method provides for the non-iterative solution of the incompressible Navier-Stokes equations by means of a fully coupled implicit technique. The solution is calculated on a body fitted computational mesh incorporating a staggered grid methodology. In the staggered grid method, the three components of vorticity are defined at the centers of the computational cell sides, while the velocity components are defined as normal vectors at the centers of the computational cell faces. The staggered grid orientation provides for the accurate definition of the vorticity components at the vorticity locations, the divergence of vorticity at the mesh cell nodes and the conservation of mass at the mesh cell centers. The solution is obtained by utilizing a fractional step solution technique in the three coordinate directions. The boundary conditions for the vorticity and velocity are calculated implicitly as part of the solution. The method provides for the non-iterative solution of the flow field and satisfies the conservation of mass and divergence of vorticity to machine zero at each time step. To test the method, the calculation of simple driven cavity flows have been computed. The driven cavity flow is defined as the flow in an enclosure driven by a moving upper plate at the top of the enclosure. To demonstrate the ability of the method to predict the flow in arbitrary cavities, results will he shown for both cubic and curved cavities.

Stremel, Paul M.↗
NASA NTRS1995

Calculated coupling efficiency between an elliptical-core optical fiber and an optical waveguide over temperature

To determine the feasibility of coupling the output of a single-mode optical fiber into a single-mode rib waveguide in a temperature varying environment, a theoretical calculation of the coupling efficiency between the two was investigated. Due to the complex geometry of the rib guide, there is no analytical solution to the wave equation for the guided modes, thus, approximation and/or numerical techniques must be utilized to determine the field patterns of the guide. In this study, three solution methods were used for both the fiber and guide fields; the effective-index method (EIM), Marcatili's approximation, and a Fourier method. These methods were utilized independently to calculate the electric field profile of each component at two temperatures, 20 C and 300 C, representing a nominal and high temperature. Using the electric field profile calculated from each method, the theoretical coupling efficiency between an elliptical-core optical fiber and a rib waveguide was calculated using the overlap integral and the results were compared. It was determined that a high coupling efficiency can be achieved when the two components are aligned. The coupling efficiency was more sensitive to alignment offsets in the y direction than the x, due to the elliptical modal field profile of both components. Changes in the coupling efficiency over temperature were found to be minimal.

Tuma, Margaret L.↗
NASA NTRS1995

Calculated quantum yield of photosynthesis of phytoplankton in the Marine Light-Mixed Layers (59 deg N, 21 deg W)

The quantum yield of photosynthesis (mol C/mol photons) was calculated at six depths for the waters of the Marine Light-Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating phi. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of phi calculated using the nonlinear regreesion method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.

Carder, K. L.↗
NASA NTRS1995

Accelerated line-by-line calculation of spectral absorption coefficients with high numerical accuracy

To model radiative transfer through the atmosphere with high accuracy, one must resort to the calculation of spectral absorption coefficients on a line-by-line basis. The calculation of these coefficients is computationally expensive for three reasons: (1) thousands of spectral lines can contribute to absorption at a single frequency; (2) the tails of spectral line profiles are long (i.e., a given line can contribute to absorption over a wide range of frequencies); and (3) the sampling frequencies at which monochromatic radiances are to be calculated must be spaced sufficiently close together to resolve the thinnest lines of interest (e.g., those that arise in the stratosphere). We have developed a new algorithm to accelerate the calculation of spectral absorption coefficients while retaining high numerical accuracy.

Sparks, L.↗
NASA NTRS1998

Design and Performance Calculations of a Propeller for Very High Altitude Flight

Reported here is a design study of a propeller for a vehicle capable of subsonic flight in Earth's stratosphere. All propellers presented were required to absorb 63.4 kW (85 hp) at 25.9 km (85,000 ft) while aircraft cruise velocity was maintained at Mach 0.40. To produce the final design, classic momentum and blade-element theories were combined with two and three-dimensional results from the Advanced Ducted Propfan Analysis Code (ADPAC), a numerical Navier-Stokes analysis code. The Eppler 387 airfoil was used for each of the constant section propeller designs compared. Experimental data from the Langley Low-Turbulence Pressure Tunnel was used in the strip theory design and analysis programs written. The experimental data was also used to validate ADPAC at a Reynolds numbers of 60,000 and a Mach number of 0.20. Experimental and calculated surface pressure coefficients are compared for a range of angles of attack. Since low Reynolds number transonic experimental data was unavailable, ADPAC was used to generate two-dimensional section performance predictions for Reynolds numbers of 60,000 and 100,000 and Mach numbers ranging from 0.45 to 0.75. Surface pressure coefficients are presented for selected angles of attack. in addition to the variation of lift and drag coefficients at each flow condition. A three-dimensional model of the final design was made which ADPAC used to calculated propeller performance. ADPAC performance predictions were compared with strip-theory calculations at design point. Propeller efficiency predicted by ADPAC was within 1.5% of that calculated by strip theory methods, although ADPAC predictions of thrust, power, and torque coefficients were approximately 5% lower than the strip theory results. Simplifying assumptions made in the strip theory account for the differences seen.

Koch, L. Danielle↗
NASA NTRS1959

Comparison of Calculated and Experimental Total-Pressure Loss and Airflow Distribution in Tubular Turbojet Combustors with Tapered Liners

Incompressible-flow calculations were performed to determine the effects of combustor geometric and operating variables on pressure loss and airflow distribution in a tubular combustor with a tapered liner. The calculations include the effects of momentum transfer between annulus and liner gas streams, annulus wall friction, heat release, and discharge coefficients of liner air-entry holes. Generalized curves are presented which show the effects of liner-wall inclination, liner open hole area, and temperature rise across the combustor on pressure loss and airflow distribution for a representative parabolic liner hole distribution. A comparison of the experimental data from 12 tapered liners with the theoretical calculations indicates that reasonable design estimates can be made from the generalized curves. The calculated pressure losses of the tapered liners are compared with those previously reported for tubular liners.

Grobman, Jack S.↗
NASA NTRS1959

A Numerical Method for Calculating the Wave Drag of a Configuration from the Second Derivative of the Area Distribution of a Series of Equivalent Bodies of Revolution

A method based on linearized and slender-body theories, which is easily adapted to electronic-machine computing equipment, is developed for calculating the zero-lift wave drag of single- and multiple-component configurations from a knowledge of the second derivative of the area distribution of a series of equivalent bodies of revolution. The accuracy and computational time required of the method to calculate zero-lift wave drag is evaluated relative to another numerical method which employs the Tchebichef form of harmonic analysis of the area distribution of a series of equivalent bodies of revolution. The results of the evaluation indicate that the total zero-lift wave drag of a multiple-component configuration can generally be calculated most accurately as the sum of the zero-lift wave drag of each component alone plus the zero-lift interference wave drag between all pairs of components. The accuracy and computational time required of both methods to calculate total zero-lift wave drag at supersonic Mach numbers is comparable for airplane-type configurations. For systems of bodies of revolution both methods yield similar results with comparable accuracy; however, the present method only requires up to 60 percent of the computing time required of the harmonic-analysis method for two bodies of revolution and less time for a larger number of bodies.

Levy, Lionel L., Jr.↗
NASA NTRS1999

Ice Accretion Calculations for a Commercial Transport Using the LEWICE3D, ICEGRID3D and CMARC Programs

Collection efficiency and ice accretion calculations were made for a commercial transport using the NASA Lewis LEWICE3D ice accretion code, the ICEGRID3D grid code and the CMARC panel code. All of the calculations were made on a Windows 95 based personal computer. The ice accretion calculations were made for the nose, wing, horizontal tail and vertical tail surfaces. Ice shapes typifying those of a 30 minute hold were generated. Collection efficiencies were also generated for the entire aircraft using the newly developed unstructured collection efficiency method. The calculations highlight the flexibility and cost effectiveness of the LEWICE3D, ICEGRID3D, CMARC combination.

Bidwell, Colin S.↗
NASA NTRS2000

Aerosol-Induced Radiative Flux Changes Off the United States Mid-Atlantic Coast: Comparison of Values Calculated from Sunphotometer and In Situ Data with Those Measured by Airborne Pyranometer

The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) measured a variety of aerosol radiative effects (including flux changes) while simultaneously measuring the chemical, physical, and optical properties of the responsible aerosol particles. Here we use TARFOX-determined aerosol and surface properties to compute shortwave radiative flux changes for a variety of aerosol situations, with midvisible optical depths ranging from 0.06 to 0.55. We calculate flux changes by several techniques with varying degrees of sophistication, in part to investigate the sensitivity of results to computational approach. We then compare computed flux changes to those determined from aircraft measurements. Calculations using several approaches yield downward and upward flux changes that agree with measurements. The agreement demonstrates closure (i.e. consistency) among the TARFOX-derived aerosol properties, modeling techniques, and radiative flux measurements. Agreement between calculated and measured downward flux changes is best when the aerosols are modeled as moderately absorbing (midvisible single-scattering albedos between about 0.89 and 0.93), in accord with independent measurements of the TARPOX aerosol. The calculated values for instantaneous daytime upwelling flux changes are in the range +14 to +48 W/sq m for midvisible optical depths between 0.2 and 0.55. These values are about 30 to 100 times the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger flux changes in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce major aerosol radiative forcing events and contribute to any global-average climate effect.

Russell, P. B.↗
NASA NTRS2000

Actinic Flux Calculations: A Model Sensitivity Study

calculate direct and diffuse surface irradiance and actinic flux (downwelling (2p) and total (4p)) for the reference model. Sensitivity analysis has shown that the accuracy of the radiative transfer flux calculations for a unit ETS (i.e. atmospheric transmittance) together with a numerical interpolation technique for the constituents' vertical profiles is better than 1% for SZA less than 70(sub o) and wavelengths longer than 310 nm. The differences increase for shorter wavelengths and larger SZA, due to the differences in pseudo-spherical correction techniques and vertical discretetization among the codes. Our sensitivity study includes variation of ozone cross-sections, ETS spectra and the effects of wavelength shifts between vacuum and air scales. We also investigate the effects of aerosols on the spectral flux components in the UV and visible spectral regions. The "aerosol correction factors" (ACFs) were calculated at discrete wavelengths and different SZAs for each flux component (direct, diffuse, reflected) and prescribed IPMMI aerosol parameters. Finally, the sensitivity study was extended to calculation of selected photolysis rates coefficients.

Krotkov, Nickolay A.↗
NASA NTRS2000

Computer Programs for Calculating the Isentropic Flow Properties for Mixtures of R-134a and Air

Three computer programs for calculating the isentropic flow properties of R-134a/air mixtures which were developed in support of the heavy gas conversion of the Langley Transonic Dynamics Tunnel (TDT) from dichlorodifluoromethane (R-12) to 1,1,1,2 tetrafluoroethane (R-134a) are described. The first program calculates the Mach number and the corresponding flow properties when the total temperature, total pressure, static pressure, and mole fraction of R-134a in the mixture are given. The second program calculates tables of isentropic flow properties for a specified set of free-stream Mach numbers given the total pressure, total temperature, and mole fraction of R-134a. Real-gas effects are accounted for in these programs by treating the gases comprising the mixture as both thermally and calorically imperfect. The third program is a specialized version of the first program in which the gases are thermally perfect. It was written to provide a simpler computational alternative to the first program in those cases where real-gas effects are not important. The theory and computational procedures underlying the programs are summarized, the equations used to compute the flow quantities of interest are given, and sample calculated results that encompass the operating conditions of the TDT are shown.

Kvaternik, Raymond G.↗