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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Comparison of three methods for calculation of helicopter rotor blade loading and stresses due to stall

A comparison is made of the results of three methods for calculating the effects of dynamic stall on the performance, airloads, and blade stresses of a helicopter rotor at high loading. The three dynamic-stall methods considered predict essentially the same performance and trim for the rotor. They give roughly the same mean bending moments, but the peak-to-peak torsion and bending moments differ by 25 to 40 percent, and there are differences in the details of the predicted blade motion and stresses. The latter are due to significant differences in the dynamic stall aerodynamic loads, particularly the aerodynamic pitch moment, predicted by the three methods.

Johnson, W.↗
NASA NTRS1979

A marching method for calculating line and continuum radiation in high energy flow fields

A method is presented for calculating nongrey radiative fluxes and intensities in a highly ionized, low temperature plasma with extreme line broadening. The method was developed to study radiative heating phenomena in the mass-injected hypersonic shock-layer environments characteristic of outer planet atmospheric entry, although it is not limited to such studies. The radiative properties model assumed local thermodynamic equilibrium and used standard continuum and molecular band models. The atomic line model, however, used a frequency-marching method for the frequency integration, which not only accounted completely for line overlapping (reabsorption) effects, but compared favorably in economy with the best equivalent-width methods. An assessment of hydrogen line-far-wing treatments, with recommendations for engineering models, is also presented.

Bolz, C. W., Jr.↗
NASA NTRS1959

Modified Matrix Method for Calculating Steady-State Span Loading on Flexible Wings in Subsonic Flight

A method is presented for shortening the computations required to determine the steady-state span loading on flexible wings in subsonic flight. The method makes use of tables of downwash factors to find the necessary aerodynamic-influence coefficients for the application of lifting-line theory. Explicit matrix equations of equilibrium are converted into a matrix power series with a finite number of terms by utilizing certain characteristic properties of matrices. The number of terms in the series is determined by a trial-and-error process dependent upon the required accuracy of the solution. Spanwise distributions of angle of attack, airload, shear, bending moment, and pitching moment are readily obtained as functions of qm(sub R) where q denotes the dynamic pressure and mR denotes the lift-curve slope of a rigid wing. This method is intended primarily to make it practical to solve steady-state aeroelastic problems on the ordinary manually operated desk calculators, but the method is also readily adaptable to automatic computing equipment.

Gainer, Patrick A.↗
NASA NTRS1975

Analytical method for calculation of navigational data for the position of a satellite

A method is described for calculating the position of a satellite at the instants when measurements are made on board. The initial conditions used were the mean orbital elements of the satellite and their time derivatives in one orbit. The results of the calculation are compared with those obtained by numerical integration, and it is found that results are identical at the beginning of an orbit, but change as the orbit progresses. The advantages and disadvantages of the analytical method are presented.

Lala, P.↗
NASA NTRS1981

A new method for calculating time-dependent atomic level populations

A method is described for reducing the number of levels to be dealt with in calculating time-dependent populations of atoms or ions in plasmas. The procedure effectively extends the collisional-radiative model to consecutive stages of ionization, treating ground and metastable levels explicitly and excited levels implicitly. Direct comparisons of full and simulated systems are carried out for five-level models.

Kastner, S. O.↗
NASA NTRS1933

Comparison of Three Methods for Calculating the Compressive Strength of Flat and Slightly Curved Sheet and Stiffener Combinations

This report gives a comparison of the accuracy of the three methods for calculating the compressive strength of flat sheet and stiffener combinations such as occur in stressed-skin or monocoque structures for aircraft. Of the three methods based upon various assumptions with regard to the interaction of sheet and stiffener, the method based upon mutual action of the stiffener and an effective width as a column gave the best agreement with the results of the tests. An investigation of the effect of small curvature resulted in the conclusion that the compressive strength of the curved panels is, for all practical purposes, equal to the strength of flat panels except for thick sheet where non-uniform curvature throughout the length may cause the strength of the curved panel to be 10 to 15 percent less than that of a corresponding flat panel.

STRESSED SKIN↗
NASA NTRS1931

A method of calculating the ultimate strength of continuous beams

The purpose of this study was to investigate the strength of continuous beams after the elastic limit has been passed. As a result, a method of calculation, which is applicable to maximum load conditions, has been developed. The method is simpler than the methods now in use and it applies properly to conditions where the present methods fail to apply.

Newlin, J A↗
NASA NTRS1989

An approximate viscous shock layer method for calculating the hypersonic flow over blunt-nosed bodies

The approximate axisymmetric method presented for accurately calculating the surface and flowfield properties of fully viscous hypersonic flow over blunt-nosed bodies incorporates the turbulence model of Cebeci-Smith (1970) and the equilibrium air tables of Hansen (1959). The method is faster than the parabolized Navier-Stokes or viscous shock layer solvers that it could replace for preliminary design determinations. Surface heat transfer and pressure predictions for the present method are comparable with the more accurate viscous shock layer method as well as flight test and wind tunnel data. A starting solution is not required.

Grantz, A. C.↗
NASA NTRS1991

A comparison of three time-dependent wave packet methods for calculating electron-atom elastic scattering cross sections

Three time-dependent wave packet methods for performing elastic scattering calculations from screened Coulomb potentials are compared. The three methods are the time-dependent amplitude density method (TDADM), a Cayley-transform method (CTM), and the Chebyshev propagation method of Tal-Ezer and Kosloff. Both the TDADM and the CTM are based on a time-dependent integral equation for the wave function. In the first, the time-dependent amplitude density is propagated, while in the other two, the wave function is propagated. As a numerical example, phase shifts and cross sections are calculated using a screened Coulomb, Yukawa type potential over the range 200-1000 eV. It is found that, in most cases, all three methods yield comparable accuracy and are about equally efficient computationally. However for l = 0, where the Coulomb well is not screened by the centrifugal potential, the TDADM requires smaller grid spacings to maintain accuracy.

Judson, Richard S.↗
NASA NTRS2009

Propellant Mass Fraction Calculation Methodology for Launch Vehicles and Application to Ares Vehicles

Propellant Mass Fraction (pmf) calculation methods vary throughout the aerospace industry. While typically used as a means of comparison between candidate launch vehicle designs, the actual pmf calculation method varies slightly from one entity to another. It is the purpose of this paper to present various methods used to calculate the pmf of launch vehicles. This includes fundamental methods of pmf calculation that consider only the total propellant mass and the dry mass of the vehicle; more involved methods that consider the residuals, reserves and any other unusable propellant remaining in the vehicle; and calculations excluding large mass quantities such as the installed engine mass. Finally, a historical comparison is made between launch vehicles on the basis of the differing calculation methodologies, while the unique mission and design requirements of the Ares V Earth Departure Stage (EDS) are examined in terms of impact to pmf.

Holt, James B.↗
NASA NTRS1987

A method for calculating turbulent boundary layers and losses in the flow channels of turbomachines

An interactive inviscid core flow-boundary layer method is presented for the calculation of turbomachine channel flows. For this method, a one-dimensional inviscid core flow is assumed. The end-wall and blade surface boundary layers are calculated using an integral entrainment method. The boundary layers are assumed to be collateral and thus are two-dimensional. The boundary layer equations are written in a streamline coordinate system. The streamwise velocity profiles are approximated by power law profiles. Compressibility is accounted for in the streamwise direction but not in the normal direction. Equations are derived for the special cases of conical and two-dimensional rectangular diffusers. For these cases, the assumptions of a one-dimensional core flow and collateral boundary layers are valid. Results using the method are compared with experiment and good quantitative agreement is obtained.

Schumann, Lawrence F.↗
NASA NTRS1987

A method for calculating turbulent boundary layers and losses in the flow channels of turbomachines

An interactive inviscid core flow-boundary layer method is presented for the calculation of turbomachine channel flows. For this method, a one-dimensional inviscid core flow is assumed. The end-wall and blade surface boundary layers are calculated using an integral entrainment method. The boundary layers are assumed to be collateral and thus are two-dimensional. The boundary layer equations are written in a streamline coordinate system. The streamwise velocity profiles are approximated by power law profiles. Compressibility is accounted for in the streamwise direction but not in the normal direction. Equations are derived for the special cases of conical and two-dimensional rectangular diffusers. For these cases, the assumptions of a one-dimensional core flow and collateral boundary layers are valid. Results using the method are compared with experiment and good quantitative agreement is obtained.

Schumann, Lawrence F.↗