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  • 1
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    Guiding principles for vortex flow controls (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In the practice of vortex flow controls, the most important factor is that the persistency and obstinacy of a concentrated vortex depend on its stability and dissipation. In this paper, the modern nonlinear stability theory for circulation-preserving flows is summarized, and the dissipation for general viscous flows is analyzed in terms of the evolution of total enstrophy. These analyses provide a theoretical base for understanding relevant physics of vortex flows, and lead to some guiding principles and methods for their controls. Case studies taken from various theoretical and/or experimental works of vortex controls, due to the present authors as well as others, confirm the feasibility of the recommended principles and methods.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-0617
    Format: text
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  • 2
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    A theoretical formulation of wave-vortex interactions (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A unified theoretical formulation for wave-vortex interaction, designated the '(omega, Pi) framework,' is presented. Based on the orthogonal decomposition of fluid dynamic interactions, the formulation can be used to study a variety of problems, including the interaction of a longitudinal (acoustic) wave and/or transverse (vortical) wave with a main vortex flow. Moreover, the formulation permits a unified treatment of wave-vortex interaction at various approximate levels, where the normal 'piston' process and tangential 'rubbing' process can be approximated dfferently.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 89-0988
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  • 3
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    Vorticity-dilatation boundary conditions for viscous compressible flows (1990)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The theoretical generalization, synthesis, and classification of various relevant formulations of the vorticity-dilatation conditioning problem is presented. Kinematic and dynamic conditions as well as differential and integral forms are considered. The possibility of using various variables that relate directly to vorticity and dilatation to construct the desired boundary conditions is examined. Some new formulations are given and previously proposed ones are located properly in the classification, and their interrelations are clarified.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Congress of Fluid Mechanics; Jan 02, 1990 - Jan 04, 1990; Cairo; Egypt
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  • 4
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    Streaming vorticity flux from oscillating walls with finite amplitude (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: How to describe vorticity creation from a moving wall is a long standing problem. This paper discusses relevant issues at the fundamental level. First, it is shown that the concept of 'vorticity flux due to wall acceleration' can be best understood by following fluid particles on the wall rather than observing the flow at fixed spatial points. This is of crucial importance when the time-averaged flux is to be considered. The averaged flux has to be estimated in a wall-fixed frame of reference (in which there is no flux due to wall acceleration at all); or, if an inertial frame of reference is used, the generalized Lagrangian mean (GLM) also gives the same result. Then, for some simple but typical configurations, the time-averaged vorticity flux from a harmonically oscillating wall with finite amplitude is analyzed, without appealing to small perturbation. The main conclusion is that the wall oscillation will produce an additional mean vorticity flux (a fully nonlinear streaming effect), which is partially responsible for the mechanism of vortex flow control by waves. The results provide qualitative explanation for some experimentally and/or computationally observed phenomena.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 8; p. 1933-1938.
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  • 5
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    Compressible flow in a diffusing S-duct with flow separation (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Local flow velocity vectors, as well as static and total pressures along ten radial traverses, were obtained at six stations for secondary flows in a diffusing 30-30-deg S-duct with circular cross section. The strong secondary flow measured in the first bend continued into the second with new vorticity produced in the opposite direction. Contour plots representing the transverse velocity field, as well as total and static pressure contours, have been obtained. As a result of the secondary flow and subsequent separation, substantial total pressure distortion is noted to occur at the duct exit.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 6
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    Gravity-jitters and excitation of slosh waves (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh waves with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 90-0655
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  • 7
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    Jet-diffuser Ejector - Attached Nozzle Design (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Attached primary nozzles were developed to replace the detached nozzles of jet-diffuser ejectors. Slotted primary nozzles located at the inlet lip and injecting fluid normal to the thrust axis, and rotating the fluid into the thrust direction using the Coanda Effect were investigated. Experiments indicated excessive skin friction or momentum cancellation due to impingement of opposing jets resulted in performance degradation. This indicated a desirability for location and orientation of the injection point at positions removed from the immediate vicinity of the inlet surface, and at an acute angle with respect to the thrust axis. Various nozzle designs were tested over a range of positions and orientations. The problems of aircraft integration of the ejector, and internal and external nozzle losses were also considered and a geometry for the attached nozzles was selected. The effect of leaks, protrusions, and asymmetries in the ejector surfaces was examined. The results indicated a relative insensitivity to all surface irregularities, except for large protrusions at the throat of the ejector.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-152361
    Format: application/pdf
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  • 8
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    Solutions of the compressible Navier-Stokes equations using the integral method (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The integral representation method was used to obtain numerical solutions of the compressible, unsteady, two-dimensional Navier-Stokes equations for subsonic flows. The equations were written with the vorticity, the dilatation, the density, and the enthalpy as the dependent variables. The method was tested by solving the following problems: the flow over a flat plate, around a circular cylinder, and around a Joukowski airfoil. The last two problems involved massive flow separation. The approach offers the capability of confining the domain of computations to the region where two quantities, the vorticity and the difference in dilatation between the real flow and the potential flow around the body, are non-negligible.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 81-0046
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  • 9
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    A study of turbulent flow between parallel plates by a statistical method (1976)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Turbulent Couette flow between parallel plates was studied from a statistical mechanics approach utilizing a model equation, similar to the Boltzmann equation of kinetic theory, which was proposed by Lundgren from the velocity distribution of fluid elements. Solutions to this equation are obtained numerically, employing the discrete ordinate method and finite differences. Two types of boundary conditions on the distribution function are considered, and the results of the calculations are compared to available experimental data. The research establishes that Lundgren's equation provides a very good description of turbulence for the flow situation considered and that it offers an analytical tool for further study of more complex turbulent flows. The present work also indicates that modelling of the boundary conditions is an area where further study is required.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-2663
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  • 10
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    A new numerical approach for compressible viscous flows (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A numerical approach for computing unsteady compressible viscous flows was developed. This approach offers the capability of confining the region of computation to the viscous region of the flow. The viscous region is defined as the region where the vorticity is nonnegligible and the difference in dilatation between the potential flow and the real flow around the same geometry is also nonnegligible. The method was developed and tested. Also, an application of the procedure to the solution of the steady Navier-Stokes equations for incompressible internal flows is presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-168842 , NAS 1.26:168842
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