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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

An asymptotic theory for the interference of large aspect ratio swept wings and multiple propeller slipstreams

This paper presents an asymptotic method for the analysis of the interference of multiple tractor propeller slipstream with large aspect ratio swept wings. It is assumed that the height of the slipstream is of the order of the wing chord and its spanwise extent is of the order of the wing span. Three different flow regions are identified by employing different stretching transformations. Asymptotic expansions are made in each of the three regions, using the chord to span ratio as the small expansion parameter. The details of the nonuniform flow in the slipstream enter into the wing sectional analysis. In the outer limit, the wing shrinks to a swept lifting line, and the slipstream reduces to a thin sheet of jet carrying the momentum gain from the propeller. The curvature of this jet sheet results in a pressure difference which is represented by a vortex sheet. The governing equations are solved by discretization. Several examples are considered for which experimental data are available. Comparison of the present results with the experimental data as well as other numerical solutions showed generally good agreement.

Prabhu, R. K.↗
NASA NTRS1980

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. II - Wall shear stress

Asymptotic methods are used to calculate the shear stress at the wall for the interaction between a normal shock wave and a turbulent boundary layer on a flat plate. A mixing length model is used for the eddy viscosity. The shock wave is taken to be strong enough that the sonic line is deep in the boundary layer and the upstream influence is thus very small. It is shown that unlike the result found for laminar flow an asymptotic criterion for separation is not found; however, conditions for incipient separation are computed numerically using the derived solution for the shear stress at the wall. Results are compared with available experimental measurements.

Liou, M. S.↗
DOE OSTI2024

Transport-driven toroidal rotation with general viscosity profile

Abstract Using the assumption of a weak normalized turbulent viscosity, usually valid in practice, the modulated-transport model (Stoltzfus-Dueck 2012 Phys. Plasmas 19 055908) is generalized to allow the turbulent transport coefficient to vary in an arbitrary way on radial and poloidal position. The new approach clarifies the physical interpretation of the earlier results and significantly simplifies the calculation, via a boundary-layer asymptotic method. Rigorous detailed appendices verify the result of the simple boundary-layer calculation, also demonstrating that it achieves the claimed order of accuracy and providing a concrete prediction for the strong plasma flows in the immediate vicinity of the last closed flux surface. The new formulas are used to predict plasma rotation at the core-edge boundary, in cases with and without externally applied torque. Dimensional formulas and extensive discussion are provided, to support experimental application of the new model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Analysis of RF Surface Loss in a Planar 2D Qubit

The Josephson junction and shunt capacitor form a transmon qubit, which is the cornerstone of modern quantum computing platforms. For reliable quantum computing, it is important how long a qubit can remain in a superposition of quantum states, which is determined by the coherence time (T1). The coherence time of a qubit effectively sets the "lifetime" of usable quantum information, determining how long quantum computations can be performed before errors occur and information is lost. There are several sources of decoherence in transmon qubits, but the predominant one is generally considered to be dielectric losses in the natural oxide layer formed on the surface of the superconductor. In this paper, we present a numerical study of microwave surface losses in planar superconducting antennas of different transmon qubit designs. An asymptotic method for estimating the energy participation ratio in ultrathin films of nanometer scales is proposed, and estimates are given for the limits of achievable minimum RF losses depending on the electrical properties of the surface oxide and the interface of the qubit with the substrate material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1974

The development of jet mixing toward the asymptotic similar solution

An analytic study of the development of an initially nonsimilar jet mixing velocity profile toward the final asymptotic, similar solution, is made. The corresponding incompressible boundary layer equations are solved for each of the streams above and below the dividing streamline by using Meksyn's asymptotic method of integration. The behavior of this flow development toward the final similar solution, as influenced by the initial condition, is properly described and discussed.

Brink, D. F.↗
NASA NTRS1975

Two-dimensional jet mixing with a pressure gradient

An analytical study of nonsimilar jet mixing is made for compressible, nonisoenergetic flows. The conservation equations are solved for each of the streams above and below the dividing streamline by using Meksyn's asymptotic method of integration for solving boundary-layer problems. The problem of laminar mixing between two parallel streams is investigated for the case of a constant pressure gradient. It is found that the velocity and temperature profiles from the exact solution to the nonsimilar governing equations can be well approximated by the locally similar solution.

Brink, D. F.↗
NASA NTRS1977

Normal shock wave-turbulent boundary layer interactions in transonic flow near separation

The problem of a normal shock wave impinging on a flat plate, turbulent boundary layer is considered for the case where the external flow is transonic. Asymptotic methods are employed. It is shown that there are two outer regions, including the outer part of the boundary layer and the external flow, in which inviscid flow governing equations hold, and two regions near the wall, in which Reynolds and/or viscous stresses need be taken into account. The solutions in the outer regions lead to the pressure distribution on the wall, for which an analytical expression is presented, valid under those conditions when separation is imminent but has not yet occurred. The solutions valid in the inner regions lead to a separation criterion.

Adamson, T. C., Jr.↗
NASA NTRS1980

Application of a numerically generated orthogonal coordinate system to the solution of inviscid axisymmetric supersonic flow over blunt bodies

A numerically generated orthogonal coordinate system (with the body surface and shock wave as opposite boundaries) was applied with a time asymptotic method to obtain steady flow solutions for axisymmetric inviscid flow over several blunt bodies including spheres, paraboloids, ellipsoids, hyperboloids, hemisphere cylinders, spherically blunted cones, and a body with a concavity in the stagnation region. Comparisons with experimental data and with the results of other computational methods are discussed. The numerically generated orthogonal coordinate system is described and applications of the method to complex body shapes, particularly those with concave regions, are discussed.

Hamilton, H. H., II↗
NASA NTRS1983

Helicopter rotor loads using matched asymptotic expansions: User's manual

Computer programs were developed to implement the computational scheme arising from Van Holten's asymptotic method for calculating airloads on a helicopter rotor blade in forward flight, and a similar technique which is based on a discretized version of the method. The basic outlines of the two programs are presented, followed by separate descriptions of the input requirements and output format. Two examples illustrating job entry with appropriate input data and corresponding output are included. Appendices contain a sample table of lift coefficient data for the NACA 0012 air foil and listings of the two programs.

Pierce, G. A.↗
NASA NTRS1985

Theory of wing rock

Wing rock is one type of lateral-directional instabilities at high angles of attack. To predict wing rock characteristics and to design airplanes to avoid wing rock, parameters affecting wing rock characteristics must be known. A new nonlinear aerodynamic model is developed to investigate the main aerodynamic nonlinearities causing wing rock. In the present theory, the Beecham-Titchener asymptotic method is used to derive expressions for the limit-cycle amplitude and frequency of wing rock from nonlinear flight dynamics equations. The resulting expressions are capable of explaining the existence of wing rock for all types of aircraft. Wing rock is developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. Good agreement between theoretical and experimental results is obtained.

Hsu, C.-H.↗
NASA NTRS1986

Time-dependent solution for axisymmetric flow over a blunt body with ideal gas, CF4, or equilibrium air chemistry

A time-asymptotic method has been used to obtain steady-flow solutions for axisymmetric inviscid flow over several blunt bodies including spheres, paraboloids, ellipsoids, and spherically blunted cones. Comparisons with experimental data and results of other computational methods have demonstrated that accurate solutions can be obtained using this approach. The method should prove useful as an analysis tool for comparing with experimental data and for making engineering calculations for blunt reentry vehicles.

Hamilton, H. H., II↗
NASA NTRS1987

The growth of Goertler vortices in compressible boundary layers

The linear instability of Goertler vortices in compressible boundary layers is considered. Using asymptotic methods in the high wavenumber regime, it is shown that a growth rate estimate can be found by solving a sequence of linear equations. The growth rate obtained in this way takes non-parallel effects into account and can be found much more easily than by ordinary differential equation eigenvalue calculations associated with parallel flow theories.

Hall, Philip↗
NASA NTRS1987

Thermochemical erosion

A quasi-steady multidimensional Stefan problem is treated by means of similarity, asymptotic methods, and numerical analysis. The continuous wearing away of a solid 'erodee' is effected by gradual consumption of a solid 'eroder'. In the process under study, the erodee melts and the (liquid) melt diffuses to the eroder, where an exothermic, indefinitely rapid, diffusion-controlled surface reaction occurs. The products of reaction convey some of the chemically-generated heat to the surface of the erodee, so that further melting may occur, and the process may proceed. The analysis seeks to estimate the quasi-steady rates of consumption of the erodee and eroder, for the (convenient) self-similar case of confocal parabolas defining the boundaries of the melt layer. The analysis is simplified by observing that the flow is of lubrication-theory type: creeping, primarily unidirectional motion owing to the thinness of the melt layer between the erodee and eroder, with diffusion of heat and mass predominantly perpendicular to the principal motion. The analysis is completed by consideration of the force balance on the eroder.

Butler, Gerald↗
NASA NTRS1988

Shock structure in classical magnetohydrodynamics

How the structure of coplanar MHD fast and slow shocks depends upon the relative magnitudes of the dissipation coefficients contained in classical magnetohydrodynamics is examined. An asymptotic method is used in which the scale lengths for resistivity, thermal conduction, and viscosity are widely separated, and the qualitative dependence of the shock solutions upon the ordering of the scales is studied. Upper limit Mach numbers for both fast and slow shocks are defined at which resistivity and thermal conduction taken together can provide all the shock dissipation and at which viscosity is not needed.

Kennel, Charles F.↗