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At least 433 records · Page 24

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NASA NTRS1985

Contact stresses in pin-loaded orthotropic plates

The effects of pin elasticity, friction, and clearance on the stresses near the hole in a pin-loaded orthotropic plate are described. The problem is modeled as a contact elasticity problem using complex variable theory, the pin and the plate being two elastic bodies interacting through contact. This modeling is in contrast to previous works which assumed that the pin is rigid or that it exerts a known cosinusoidal radial traction on the hole boundary. Neither of these approaches explicitly involves a pin. A collocation procedure and iteration were used to obtain numerical results for a variety of plate and pin elastic properties and various levels of friction and clearance. Collocation was used to enforce the boundary and iteration was used to find the contact and no-slip regions on the boundary. Details of the numerical scheme are discussed.

Hyer, M. W.↗

NASA NTRS1985

Simulation of turbulent mixing layers

A hybrid numerical scheme, combined with a scalar convection scheme, is used to compute turbulent mixing layers. The hybrid scheme is used to solve the vorticity equation by dividing the domain into two regions, applying a Lagrangian method in one region and an Eulerian method in the other. The scalar convection scheme is used to track an interface which separates a dyed fluid from a dye-free fluid, thereby distinguishing the fluid that starts on the high speed side from the fluid that starts on the low speed side. A two-dimensional mixing layer has been simulated using this new method; the roll up of a vortex sheet into structures that interact and pair is observed. The growth of the momentum thickness and the development of the mean turbulence statistics are found to be consistent with experimental observations. Forcing of the layer at moderate and low frequencies shows a dramatic effect on the growth of the momentum thickness and the entrainment ratio. Low frequency forcing enhances the growth of the layer; moderate frequency forcing inhibits the growth.

Mansour, N. N.↗

NASA NTRS1986

Transonic aeroelasticity of wings with tip stores

The presence of tip stores influences both aerodynamic and aeroelastic performances of wings. Such effects are more pronounced in the transonic regime. In this study, transonic aeroelasticity of wings with tip stores is studied for the first time by a theoretical method using the unsteady-small disturbance transonic aerodynamic equations coupled with modal structural equations of motion. The aerodynamic and structural equations of motion are simultaneously integrated by a time-accurate numerical scheme. To validate the tip store simulation, aeroelastic computations are made for a typical rectangular wing with a tip store and results are correlated with available wind tunnel data for the corresponding wing without a tip store at various flight conditions. Aeroelastic computations are also made for a typical fighter wing with a tip store. Present computations show that it is important to account for the aerodynamics of the tip store, particularly in the transonic regime where the tip store can make the wing aeroelastically unstable.

Guruswamy, G. P.↗

NASA NTRS1986

A spline-based parameter estimation technique for static models of elastic structures

The problem of identifying the spatially varying coefficient of elasticity using an observed solution to the forward problem is considered. Under appropriate conditions this problem can be treated as a first order hyperbolic equation in the unknown coefficient. Some continuous dependence results are developed for this problem and a spline-based technique is proposed for approximating the unknown coefficient, based on these results. The convergence of the numerical scheme is established and error estimates obtained.

Dutt, P.↗

NASA NTRS1987

Numerical simulation of transonic propeller flow using a 3-dimensional small disturbance code employing novel helical coordinates

The numerical simulation of three-dimensional transonic flow about propeller blades is discussed. The equations for the unsteady potential flow about propellers is given for an arbitrary coordinate system. From this the small disturbance form of the equation is derived for a new helical coordinate system. The new coordinate system is suited to propeller flow and allows cascade boundary conditions to be applied straightforward. A numerical scheme is employed which solves the steady flow as an asymptotic limit of unsteady flow. Solutions are presented for subsonic and transonic flow about a 5 percent thick bicircular arc blade of an eight bladed cascade. Both high and low advance ratio cases are given which include a lifting case as well as nonlifting cases. The nonlifting cases are compared to solutions from a Euler code.

Snyder, Aaron↗

NASA NTRS1986

Computer code for gas-liquid two-phase vortex motions: GLVM

A computer program aimed at the phase separation between gas and liquid at zero gravity, induced by vortex motion, is developed. It utilizes an explicit solution method for a set of equations describing rotating gas-liquid flows. The vortex motion is established by a tangential fluid injection. A Lax-Wendroff two-step (McCormack's) numerical scheme is used. The program can be used to study the fluid dynamical behavior of the rotational two-phase fluids in a cylindrical tank. It provides a quick/easy sensitivity test on various parameters and thus provides the guidance for the design and use of actual physical systems for handling two-phase fluids.

Yeh, T. T.↗

NASA NTRS1986

Some aspects of vortex flows determined from the thin-layer Navier-Stokes equations

Vortex flows caused by a swept wing are described in some detail. The thin-shear-layer Navier-Stokes equations with an algebraic eddy-viscosity turbulence model are solved. An implicit, factored numerical scheme is used. On the upper surface of the wing, flow is primarily along the free-stream and spanwise direction, respectively, at small and large angles of attack.

Mehta, Unmeel↗

NASA NTRS1986

A model of inner cometary ionospheres

A hydrodynamical model to describe the movement of the thermalized charged components in the inner ionosphere of comet Halley is presented. Photoelectrons are included by applying a two-stream-type approach. The numerical scheme describes shock transitions in a natural way. Solutions are obtained for a number of different assumptions concerning electron heating rates but all show that the electron temperature increases sharply where the collisional electron neutral coupling becomes unimportant. This temperature increase is accompanied by an increase in the plasma pressure and in its associated polarization electric field, and causes the plasma flow to go subsonic. In certain cases this transition occurs as an inner shock which may explain the observed ion pile-up in Halley's comet.

Korosmezey, A.↗

NASA NTRS1987

An implementation of a barotropic quasigeostrophic model of ocean circulation on the MPP

The implementation on the Massively Parallel Processor (MPP) of a barotropic quasigeostrophic model of ocean circulation is discussed. The mathematical model, including scalings and boundary conditions is discussed. The numerical scheme, which uses compact differencing is also discussed. The implementation of this model on the MPP is then presented. Finally, some performance results are given and compared to results obtained using the VPS-32 and one processor of a CRAY-2.

Grosch, C. E.↗

NASA NTRS1986

Reynolds stress closure in jet flows using wave models

A wave model was developed for the two dimensional shear layer. This configuration is being used as a test case for the closure schemes. Numerical methods are under development to solve the nonseparable Rayleigh equation. A model problem is being used to assist in the algorithm development. An analytic solution of the Rayleigh equation for a basic elliptic flow was obtained. This will be used to verify the stability codes developed for arbitrary geometries. Other numerical methods for solving the Rayleigh equation based on the boundary element technique are being examined.

Morris, P. J.↗

NASA NTRS1985

Nonlinear acoustic wave propagation in atmosphere. Absorbing boundary conditions for exterior problems

Elliptic and hyperbolic problems in unbounded regions are considered. These problems, when one wants to solve them numerically, have the difficulty of prescribing boundary conditions at infinity. Computationally, one needs a finite region in which to solve these problems. The corresponding conditions at infinity imposed on the finite distance boundaries should dictate the boundary conditions at infinity and be accurate with respect to the interior numerical scheme. The treatment of these boundary conditions for wave-like equations is discussed.

Hariharan, S. I.↗

NASA NTRS1987

On the interaction of small and large eddies in two dimensional turbulent flows

Some results concerning the interaction of small and large eddies to two dimensional turbulent flows are presented. It is shown that the amplitude of small structures decays exponentially to a small value, and from this is inferred a simplified interaction law of small and large eddies. Beside their intrinsic interest for the understanding of the physics of turbulence, these results lead to new numerical schemes to be studied in a separate work.

Foias, C.↗

NASA NTRS1986

Computation of turbulent supersonic flows around pointed bodies having crossflow separation

The numerical method developed by Schiff and Sturek (1980) on the basis of the thin-layer parabolized Navier-Stokes equations of Schiff and Steger (1980) is extended to the case of turbulent supersonic flows on pointed bodies at high angles of attack. The governing equations, the numerical scheme, and modifications to the algebraic eddy-viscosity turbulence model are described; and results for three cones and one ogive-cylinder body (obtained using grids of 50 nonuniformly spaced points in the radial direction between the body and the outer boundary) are presented graphically and compared with published experimental data. The grids employed are found to provide sufficient spatial resolution of the leeward-side vortices; when combined with the modified turbulence model, they are shown to permit accurate treatment of flows with large regions of crossflow separation.

Degani, D.↗

NASA NTRS1986

Using Hough harmonics to validate and assess nonlinear shallow-water models

The implementation of a technique for locating programming errors in shallow-water codes, establishing the correctness of the code, and assessing the performance of the numerical model under various flow conditions is described. The right-hand side of the differential equations is modified in such a way that the exact solution of the nonlinear initial-value problem is known, so that the truncation errors of the numerical scheme can be studied in detail. The exact solution is prescribed to be any linear combination of Hough harmonics which propagate in time according to their natural frequencies.

Dee, Dick P.↗

NASA NTRS1987

Transonic aeroelasticity of wings with active control surfaces

Transonic aeroelasticity of wings with active control surfaces is studied by using the unsteady-small disturbance transonic aerodynamic equations coupled with modal structural equations of motion. The aerodynamic and structural equations of motion are simultaneously integrated by a time-accurate numerical scheme. A procedure of synthesizing active controls with unsteady transonics is presented. Flutter suppression in the transonic regime using active controls is demonstrated for a rectangular wing. Characteristics of a selected control law in the transonic regime are studied. The results from this study are useful in the design of active control systems in the transonic regime.

Guruswamy, Guru P.↗

NASA NTRS1987

Numerical simulation of transonic propeller flow using a three-dimensional small disturbance code employing novel helical coordinates

Snyder, Aaron↗

NASA NTRS1987

Application of the CSCM method to the design of wedge cavities

This paper describes the application of the conservative supra characteristic method (CSCM) to predict the flow around two-dimensional slot injection cooled cavities in hypersonic flow. Seven different numerical solutions are presented that model three different experimental designs. The calculations manifest outer flow conditions including the effects of nozzle/lip geometry, angle of attack, nozzle inlet conditions, boundary and shear layer growth and turbulance on the surrounding flow. The calculations were performed for analysis prior to wind tunnel testing for sensitivity studies early in the design process. Qualitative and quantitative understanding of the flows for each of the cavity designs and design recommendations are provided. The present paper demonstrates the ability of numerical schemes, such as the CSCM method, to play a significant role in the design process.

Venkatapathy, Ethiraj↗

NASA NTRS1987

A new model of cometary ionospheres

The coupled continuity, momentum, and energy equations were solved for ionospheric conditions appropriate for Comet Halley at 1 AU. The numerical scheme used is such that any shock transition appears naturally in the solution and no a priori assumptions are necessary. Solutions were obtained for a number of different assumptions concerning electron heating rates, but all showed that the electron temperatures increase rapidly and significantly at a distance from the nucleus where collisional electron-neutral cooling becomes unimportant. This temperature increase is accompanied by a sharp increase in both the plasma pressure and its associated polarization electric field, causing the supersonic plasma flow to go subsonic. It is not clear at this time whether or not this sonic transition is accompanied by a shock.

Korosmezey, A.↗