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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The prediction of normal force and rolling moment coefficients for a spinning wing

Nonlinear airfoil section data for angles of attack from 0 to 180 deg were used in a small computer code to numerically integrate the section normal force coefficients along the span as a function of the local velocity and angle of attack resulting from the combined spinning and descending motion. A correction was developed to account for the radial pressure gradient in the separated, rotating flow region above the wing. This correction was found to be necessary in order to obtain agreement, both in form and magnitude, with rotary balance test data.

Mccormick, B. W.↗
NASA NTRS1981

Numerical solution of transonic stream function equation

The stream function equation, in conservation form, looks similar to the full potential equation and existing methods (e.g. artificial compressibility) can be readily applied. Rotational flows can be calculated once the vorticity (due to shocks or nonuniformity) is evaluated. There are, however, two main difficulties: First, the density is not uniquely determined in terms of the flux (there are two solutions; the subsonic and the supersonic branch with a square root singularity at the sonic point). Methods to overcome this difficulty are studied and results are presented with some remarks on inviscid separation and closed stream lines. Second, the need of two stream functions for three dimensional calculations is briefly discussed.

Hafez, M.↗
NASA NTRS1982

An experimental study of the effect of tail configuration on the spinning characteristics of general aviation aircraft

The feasibility of using static wind tunnel tests to obtain information about spin damping characteristics of an isolated general aviation aircraft tail was investigated. A representative tail section was oriented to the tunnel free streamline at angles simulating an equilibrium spin. A full range of normally encountered spin conditions was employed. Results of parametric studies performed to determine the effect of spin damping on several tail design parameters show satisfactory agreement with NASA rotary balance tests. Wing and body interference effects are present in the NASA studies at steep spin attitudes, but agreement improves with increasing pitch angle and spin rate, suggesting that rotational flow effects are minimal. Vertical position of the horizontal stabilizer is found to be a primary parameter affecting yaw damping, and horizontal tail chordwise position induces a substantial effect on pitching moment.

Ballin, M. G.↗
NASA NTRS1982

An estimation of aerodynamic forces and moments on an airplane model under steady state spin conditions

The problem of estimating the aerodynamic characteristics of a wing body configuration of a spinning airplane at extreme angles of attack and spin rates is approached by the application of strip theory. Semiempirical methods are used to estimate the aerodynamic force distributions over each component using static, nonrotational wind-tunnel test data. To these predictions, corrections are applied to account for the primary rotational flow effects which are significant at large spin rates. The results of this modified strip theory are shown to be in good agreement with spin tunnel rotary balance test data.

Pamadi, B. N.↗
NASA NTRS1982

Planetary-scale characteristics of the atmospheric circulation during January and February 1979

The global scale mass and wind fields observed during FGGE special observing period (SOP) are studied, with attention given to the time variation and vertical structure of the ultralong waves. A spherical harmonic representation is developed for the global fields. The tropical circulation is found to imprint more amplitude on the lower-order components than the midlatitude circulation does. High amplitude oscillations are determined to be present in the divergent fields on all time scales, i.e., diurnal to monthly. The global scale wind was found to change on scales approaching a week. Good agreement with teleconnection predictions was demonstrated for the cross-equatorial divergent and zonal rotational flow changes. The global scale was concluded to resemble force modes of linear tidal theory, with important contributions from longitudinal heating gradients.

Paegle, J.↗
NASA NTRS1983

Influence of airplane components on rotational aerodynamic data for a typical single-engine airplane

The influence of airplane components, as well as wing location and tail length, on the rotational flow aerodynamics is discussed for a 1/6-scale general aviation airplane model. Examination of the individual component effects provides insight as to the source of the moment and forces that determine spin characteristics. For the subject airplane, it is seen that the presence of the horizontal tail adversely effects the yaw damping of the vertical tail such that at certain angles of attack the vertical actually becomes a propelling component in spinning motion. It is shown that the level of this adverse interaction is a function of the relative positions of the wing and the tail surfaces, e.g., relocating the wing to the high wing position or shortening the tail moment arm from the basic configuration both reduced or eliminated the adverse tail interference for certain angles of attack. The influence of wing location on the damping characteristics of the horizontal-vertical tail combination would not be addressed in any existing tail design criterion for spinning and could only be discerned through rotary balance testing.

Ralson, J.↗
NASA NTRS1983

A vortex venturi for reverting antimisting fuel properties

The level of degradation of antimisting fuel polymers such as FM-9 which must be accomplished in order to use antimisting fuel in existing engines may require the use of cavitation. The hydrodynamic shear produced by the collapse of vapor bubbles is capable of producing more splitting of polymeric molecules than mechanically-induced shear. A program has been carried out to investigate the possibility of using a cavitating venturi with rotating flow as a fuel reverter. This investigation included the effects of a swirl-inducing twisted tape upstream of the throat, inlet pressure, recovery pressure ratio and a pintle for varying throat area. A correlation of the data was produced, system concepts for using the vortex venturi were investigated and problem areas were delineated.

Szetela, E. J.↗
NASA NTRS1985

Comet Thermal Modeling

Past thermal models of cometary nuclei have tended to be restricted to hemispherical averages and have ignored many important effects such as surface heat flow, rotation period, or coma opacity. A computer based model called KRC/COM was developed which includes these and many other important effects to give a more accurate physical model of sublimation from icy cometary nuclei. Halley's Comet was used as a test case because of the high interest in the 1986 perihelion passage of that comet.

Weissman, P. R.↗
NASA NTRS1984

Estimation of aerodynamic forces and moments on a steadily spinning airplane

A semiempirical method is presented for the estimation of aerodynamic forces and moments on a steadily rotating airplane model in a spin tunnel. The approach is based on the application of strip theory to determine a part of the aerodynamic coefficient (including rotational velocity) and then estimation of increments to these coefficients because of rotational flow over the stalled airplane. The theory is applied to a light, single-engine, general aviation airplane and the results are compared with the corresponding spin tunnel rotary balance test data.

Pamadi, B. N.↗
NASA NTRS1985

Accelerated solution of the steady Euler equations

The present paper is concerned with two methods for the accelerated solution of the steady Euler equations. One method makes use of a second-order embedding to facilitate the derivation of the relaxation solution of the steady equations of motion, while the other method employs a multile-gridding concept to accelerate the convergence of a simple, explicit, time-marching scheme applied to the unsteady equations. It is pointed out that the surrogate equation technique provides a means for formulating problems involving the full steady Euler equations in such a way as to allow the use of relaxation solution procedures. It is, therefore, possible to solve either irrotational or rotational flow problems spanning the entire spectrum of subsonic, transonic, and supersonic conditions. The solutions can be obtained without an employement of either derived dependent variables, semidirect methods, or an unsteady formulation.

Johnson, G. M.↗
NASA NTRS1986

A new approach for solving the three-dimensional steady Euler equations. I - General theory

The present iterative procedure combines the Clebsch potentials and the Munk-Prim (1947) substitution principle with an extension of a semidirect Cauchy-Riemann solver to three dimensions, in order to solve steady, inviscid three-dimensional rotational flow problems in either subsonic or incompressible flow regimes. This solution procedure can be used, upon discretization, to obtain inviscid subsonic flow solutions in a 180-deg turning channel. In addition to accurately predicting the behavior of weak secondary flows, the algorithm can generate solutions for strong secondary flows and will yield acceptable flow solutions after only 10-20 outer loop iterations.

Chang, S.-C.↗
NASA NTRS1985

The influence of tropical wind data on the analysis and forecasts of the GLAS GCM for the Global Weather Experiment

Several densities of tropical divergent wind data were included in a fourth-order GCM to examine the effects on the accuracy of the model predictions. The experiments covered assimilation of all available tropical wind data, no tropical wind data between 20 deg N and 20 deg S, only westerly tropical wind data and only easterly tropical wind data. The predictions were all made for the 200 mb upper troposphere. Elimination of tropical data produced excessively strong upper tropospheric westerlies which in turn amplified the globally integrated rotational flow kinetic energy by around 10 percent and doubled the global divergent flow kinetic energy. Retaining only easterly wind data, ameliorated most of the error. Inclusion of all the tropical wind data however, did not lead to overall positive effects, as the data were linked to tropical wave energetics and ageostrophic winds which were already assimilated in the model.

Paegle, J.↗
NASA NTRS1986

Interaction of decaying trailing vortices in ground shear

The drift of trailing vortices in a cross wind near to the ground is modeled by an unsteady, two-dimensional, rotational flowfield with a concentration of large vorticity in spots having finite total strength. The problem is analyzed by a combination of the method of matched asymptotic analyses for the decay of the vortical spots and the Euler solution for the unsteady rotational flow. A primary feature of the numerical scheme is that the grid size and time step depend only the length and velocity scales of the background flow and is independent of the effective core size of a vortical spot which can be much smaller than the grid size. Numerical results are presented to demonstrated the strong interaction between the trajectjories of the vortical spots and the redistribution of vorticity in the background flowfield.

Liu, C. H.↗
NASA NTRS1987

A three-dimensional dual potential procedure for inlets and indraft wind tunnels

A dual potential decomposition of the velocity field into a scalar and a vector potential function is extended to three dimensions and used in the finite-difference simulation of steady three-dimensional inviscid rotational flow through ducts and inlets. The procedure has been used to simulate the flow through the 80- by 120-Foot Wind Tunnel at NASA Ames Research Center. Vanes and screens located at the entrance of the inlet are modeled using actuator disk theory. The numerical predictions are in good agreement with experimental data.

Rao, K. V.↗
NASA NTRS1988

Nonlinear thermal instability in the solar transition region

Ways in which the radiation-driven thermal instability might affect the structure of the solar atmosphere are considered. It is found that the ultimate state of the medium is highly sensitive to the evolving modal content of the perturbation in that both the initial modal composition and the extent of mode coupling determine the final structure of the atmosphere. It is also found that the condensation process generates highly rotational flows during and after the transition to a new stable state.

Karpen, Judith T.↗
NASA NTRS1989

Effects of nonlinear aerodynamics and static aeroelasticity on mission performance calculations for a fighter aircraft

During conceptual design studies of advanced aircraft, the usual practice is to use linear theory to calculate the aerodynamic characteristics of candidate rigid (nonflexible) geometric external shapes. Recent developments and improvements in computational methods, especially computational fluid dynamics (CFD), provide significantly improved capability to generate detailed analysis data for the use of all disciplines involved in the evaluation of a proposed aircraft design. A multidisciplinary application of such analysis methods to calculate the effects of nonlinear aerodynamics and static aeroelasticity on the mission performance of a fighter aircraft concept is described. The aircraft configuration selected for study was defined in a previous study using linear aerodynamics and rigid geometry. The results from the previous study are used as a basis of comparison for the data generated herein. Aerodynamic characteristics are calculated using two different nonlinear theories, potential flow and rotational (Euler) flow. The aerodynamic calculations are performed in an iterative procedure with an equivalent plate structural analysis method to obtain lift and drag data for a flexible (nonrigid) aircraft. These static aeroelastic data are then used in calculating the combat and mission performance characteristics of the aircraft.

Giles, Gary L.↗
NASA NTRS1990

Correction and update to 'The earth's C21 and S21 gravity coefficients and the rotation of the core'

Wahr (1987) used satellite constraints on C21 and S21 (the spherical harmonic coefficients of the earth's external gravitational potential) to infer certain properties of the core and core/mantle boundary. It is shown here, contrary to the claim by Wahr, that it is not possible to use C21 and S21 to placed bounds on the core's products of inertia. As a result, Wahr's constraints on the l = 2, m = 1 components of the core/mantle boundary topography and on the angular orientation of the inner core with respect to the earth's rotation vector are not justified. On the other hand, Wahr's conclusions about the time-averaged torque between the core and mantle and the resulting implications for the l = 2, m = 1 components of fluid pressure at the top of the core can be strengthened. Wahr's conclusions about the mean rotational flow in the core are unaltered.

Wahr, John↗
NASA NTRS1990

Integrated support structure for GASCAN 2

The focus of the Worcester Polytechnic Institute (WPI) Advanced Space Design Program was the preliminary design of the Integrated Support Structure for GASCAN II, a Get Away Special canister donated by the MITRE Corporation. Two teams of three students each worked on the support structure. There was a structural design team and a thermal design team. The structure will carry three experiments also undergoing preliminary design this year, the mu-gravity Ignition Experiment, the Rotational Flow in Low Gravity Experiment, and the Ionospheric Properties and Propagation Experiment. The structural design team was responsible for the layout of the GASCAN and the preliminary design of the structure itself. They produced the physical interface specifications defining the baseline weights and volumes for the equipment and produced layout drawings of the system. The team produced static and modal finite element analysis of the structure using ANSYS. The thermal design team was responsible for the power and timing requirements of the payload and for the identification and preliminary analysis of potential thermal problems. The team produced the power, timing, and energy interface specifications and assisted in the development of the specification of the battery pack. The thermal parameters of each experiment were cataloged and the experiments were subjected to worst case heat transfer scenarios.

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