5,950 research outputs found

    Experiences with optimizing airfoil shapes for maximum lift over drag

    Get PDF
    The goal was to find airfoil shapes which maximize the ratio of lift over drag for given flow conditions. For a fixed Mach number, Reynolds number, and angle of attack, the lift and drag depend only on the airfoil shape. This then becomes a problem in optimization: find the shape which leads to a maximum value of lift over drag. The optimization was carried out using a self contained computer code for finding the minimum of a function subject to constraints. To find the lift and drag for each airfoil shape, a flow solution has to be obtained. This was done using a two dimensional Navier-Stokes code

    An investigation of turbulence models

    Get PDF
    The accuracy to which a turbulent boundary layer or wake can be predicted numerically depends on the validity of the turbulence closure model used. The modeling of turbulence physics is one of the most difficult problems in computational fluid dynamics (CFD). In fact, it is one of the pacing factors in the development of CFD. In general, there are three main approaches to the description of trubulence physics. First is turbulence modeling in which the Reynolds averaged Navier-Stokes equations are used and some closure approximation is made for the Reynolds stresses. A second approach to turbulence is large eddy simulation (LES) in which the computational mesh is taken to be fine enough that the large scale structure of the turbulence can be calculated directly. An empirical assumption must be made for the small scale sub-grid turbulence. The third approach is direct simulation. In this technique the Navier-Strokes equations are solved directly on a mesh which if fine enough to resolve the smallest length scale of the turbulence. The Reynolds averaged equations are not used and no closure assumption is required. These last two approaches require extensive computer resources and as such are not engineering tools. The purpose of the work was to investigate the various engineering turbulence models for accuracy and ease of programming. This involved comparison of the models with each other and with experimental data

    Finite-volume scheme for transonic potential flow about airfoils and bodies in an arbitrarily shaped channel

    Get PDF
    A conservative finite-volume difference scheme is developed for the potential equation to solve transonic flow about airfoils and bodies in an arbitrarily shaped channel. The scheme employs a mesh which is a nearly conformal O mesh about the airfoil and nearly orthogonal at the channel walls. The mesh extends to infinity upstream and downstream, where the mapping is singular. Special procedures are required to treat the singularities at infinity, including computation of the metrics near those points. Channels with exit areas different from inlet areas are solved; a body with a sting mount is an example of such a case

    The Average Kinetic Energy of the Superconducting State

    Full text link
    Isothermal magnetization curves are plotted as the magnetization times the magnetic induction, 4πMB4 \pi M \cdot B, versus the applied field, H. We show here that this new curve is the average kinetic energy of the superconducting state versus the applied field, for type-II superconductors with a high Ginzburg-Landau parameter κ\kappa. The maximum of 4πMB4 \pi M \cdot B occurs at a field, HH^{*}, directly related to the upper critical field, Hc2H_{c2}, suggesting that Hc2(T)H_{c2}(T) may be extracted from such plots even in cases when it is too high for direct measurement. We obtain these plots both theoretically, from the Ginzburg-Landau theory, and experimentally, using a Niobium sample with Tc=8.5KT_c = 8.5 K, and compare them.Comment: 11 pages, 9 postscript figure

    Implications of Screen Use in Young Children\u27s Occupations

    Get PDF
    Introduction: OTs need to address both the duration and quality of screen media children use, to promote their development and participation in healthy occupations

    New Faraday lines through Four Bosons EM

    Full text link
    Field physics was founded by Faraday introducing magnetic fields (1831), electric fields (1837) and light as an EM wave (1846), initiating the process where nature is made by matter and fields. Consider that, ordinary space is full of fields. The Faraday view is basis for modern quantum field theory. The concept of fields set up a physicality in development. Physics would like to know how far matter is created by fields. Generate matter from nonlinear fields. Faraday lines of force relating physical entities as electric charge and mass depending on fields. Our purpose is on Faraday lines for nonlinear abelian electromagnetism. Introduce the Four Bosons EM. The phenomenology of a generic charge {+,0,}\{+,0,-\} transmitted by four bosons {Aμ,Uμ,Vμ±}\{A_{\mu}, U_{\mu}, V_{\mu}^{\pm}\}. Nonlinear equations constituted. New Faraday lines were introduced. The potentials fields of physics are developed. Granular and collective fields strengths expressed. Four types of fields charges are derived. They are electric charge, modulated, neutral, Bianchi. This work introduces a systematic procedure of associative physics. Mass and charge are generated due to the four fields interrelationships. Masses are derived without spontaneous symmetry breaking. It is obtained naturally from gauge symmetry, London, and mixing terms. Electric charge is written by fields through the Noether theorem. EM interactions not necessarily coupled with electric charge are proposed. An enlargement of EM energy is derived.Comment: 20 pages, 0 figure

    Electric Charge Mutation by Four Vector Bosons

    Full text link
    A general theory of electric charge is proposed. It is based on two phenomenologies. Electric charge mutation and conservation law. Three charges {+,,0}\{ +, - ,0\} transformations physics succeeds. Quantum field theory underlies corresponding creations and annihilation. A potential field's quadruplet is ruled. Microscopic electromagnetism is processed by four vectors bosons intermediations. The electromagnetism closure is accomplished. The quadruplet AμI{Aμ,Uμ,Vμ±}A_{\mu I} \equiv \{ A_\mu, U_\mu, V_\mu^\pm\} completeness introduces the most generic EM energy flux between electric charges. Charge mutation includes that besides usual photon, EM phenomena is enlarged by massive and charged photons. Charge conservation associates these four vector fields. Electric charge symmetry, extends EM for an abelian symmetry UQU(1)×SO(2)globalU_{Q} \equiv U(1) \times SO(2)_{global}. A new EM Lagrangian beyond Maxwell results. A symmetry equation for electric charge is established through Noether theorem. The electric charge transfer physics extends the EM phenomenon. Nonlinear Electromagnetic fields modified electric charge symmetry, new EM regimes. Potential fields become a physical entity producing conglomerates, collective fields, mass, sources, charges, monopoles, forces. EM features ruled from an extended electric charge abelian symmetry. Systemic, nonlinear, neutral, spintronics, photonics, electroweak EM regimes are constituted.Comment: 45 pages, not figur
    corecore