Showing papers on "Incompressible flow published in 1977"

Computational Design of the Basic Dynamical Processes of the UCLA General Circulation Model

Abstract: The 12-layer UCLA general circulation model encompassing troposphere and stratosphere (and superjacent 'sponge layer') is described. Prognostic variables are: surface pressure, horizontal velocity, temperature, water vapor and ozone in each layer, planetary boundary layer (PBL) depth, temperature, moisture and momentum discontinuities at PBL top, ground temperature and water storage, and mass of snow on ground. Selection of space finite-difference schemes for homogeneous incompressible flow, with/without a free surface, nonlinear two-dimensional nondivergent flow, enstrophy conserving schemes, momentum advection schemes, vertical and horizontal difference schemes, and time differencing schemes are discussed.

Finite Element Techniques for Fluid Flow

Abstract: Finite element techniques for fluid flow , Finite element techniques for fluid flow , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

The laminar separation of an incompressible fluid streaming past a smooth surface

Abstract: Sychev's (1972) proposal, that in general the laminar separation and breakaway of an incompressible fluid streaming past a smooth surface (e.g. on a bluff body) takes place through a triple-deck structure around the separation point, is examined numerically in this paper. The proposed pattern for large Reynolds number ($Re$) flows is based on a modification of the classical Kirchhoff (1869) free streamline theory, in which a slight adverse pressure gradient is provoked in the inviscid motion immediately ahead of the breakaway. This pressure gradient is just enough to generate a triple-deck development closer to the separation point. The major task then is to decide whether or not a solution of the basic triple-deck problem exists, and is regular at separation, and if it is unique. The numerical investigation, an iterative calculation of the relevant boundary layer problem, together with the potential flow relation between the unknown pressure and displacement, points fairly firmly to both the existence and uniqueness of a solution. Thus, for the bluff body problem when $Re$ $\gg $ 1, the triple-deck determines exactly how far the separation point lies from the position implied by inviscid (Kirchhoff) theory. Comparisons with separating incompressible fluid motions determined numerically from the Navier-Stokes equations and measured experimentally give some support overall to the triple-deck description. For the flow past a circular cylinder the agreement in the variation of pressure and skin friction near separation is in general very encouraging, for Reynolds numbers as low as 30.

Unsteady aerodynamic modeling for arbitrary motions

Abstract: Results indicating that unsteady aerodynamic loads derived under the assumption of simple harmonic motions executed by airfoil or wing can be extended to arbitrary motions are summarized. The generalized Theodorsen (1953) function referable to loads due to simple harmonic oscillations of a wing section in incompressible flow, the Laplace inversion integral for unsteady aerodynamic loads, calculations of root loci of aeroelastic loads, and analysis of generalized compressible transient airloads are discussed.

Solution of three-dimensional incompressible flow problems

Abstract: A method for solving quite general three-dimensional incompressible flow problems, in particular those described by the Navier-Stokes equations, is presented. The essence of the method is the expression of the velocity in terms of scalar and vector potentials, which are the three-dimensional generalizations of the two-dimensional stream function, and which ensure that the equation of continuity is satisfied automatically. Although the method is not new, a correct but simple and unambiguous procedure for using it has not been presented before.

The Secondary Flow of Newtonian Fluids in Cone‐and‐Plate Viscometers

Abstract: Secondary flow in cone‐and‐plate viscometers is studied by numerical integration of the equations of motion for steady incompressible flow of Newtonian fluids. Solutions over wide ranges of the two principal parameters, Reynolds number and gap angle, yield detailed information on the flow fields and elements of the rate of deformation tensor. Secondary flows are shown to cause large deviations in certain elements of the rate of deformation at Reynolds numbers more than an order of magnitude lower than those at which the torque is appreciably changed. Comparisons are given with prior analytical and experimental work.

Computation of the flow between two rotating coaxial disks

Abstract: A numerical investigation of the problem of rotating disks is made using the Newton–Raphson method. It is shown that the governing equations may exhibit one, three or five solutions. A physical interpretation of the calculated profiles will be presented. The results computed reveal that both Batchelor and Stewartson analysis yields for high Reynolds numbers results which are in agreement with our observations, i.e. the fluid may rotate as a rigid body or the main body of the fluid may be almost at rest, respectively. Occurrence of a two-cell situation at particular branches will be discussed.

Self-preserving turbulent wall jets over convex surfaces

Abstract: The flow of an ostensibly two-dimensional wall jet over a logarithmic spiral has been studied both experimentally and theoretically. It is established that, if the skin friction is effectively constant, the flow may be self-preserving, and this is confirmed experimentally for the two spirals studied (.

A general method for calculating three-dimensional compressible laminar and turbulent boundary layers on arbitrary wings

Abstract: The method described utilizes a nonorthogonal coordinate system for boundary-layer calculations It includes a geometry program that represents the wing analytically, and a velocity program that computes the external velocity components from a given experimental pressure distribution when the external velocity distribution is not computed theoretically The boundary layer method is general, however, and can also be used for an external velocity distribution computed theoretically Several test cases were computed by this method and the results were checked with other numerical calculations and with experiments when available A typical computation time (CPU) on an IBM 370/165 computer for one surface of a wing which roughly consist of 30 spanwise stations and 25 streamwise stations, with 30 points across the boundary layer is less than 30 seconds for an incompressible flow and a little more for a compressible flow

A finite element convergence study for accelerating flow problems

Abstract: The convergence properties of several non-linear solution procedures were examined with respect to the accelerated flow of a fluid in a converging channel (the Hamel problem), using two different finite element computer programs with different elemental construction. The Reynolds number varied from that for creeping flow to 1088 without exceeding the radius of convergence. Special attention was given to the successive substitution and Newton–Raphson solution algorithms, with a significant advantage in rate of convergence noted for the latter.

Computing internal viscous flow problems for the circle by integral methods

Abstract: Steady two-dimensional viscous motion within a circular cylinder generated by (a) the rotation of part of the cylinder wall and (b) fluid entering and leaving through slots in the wall is considered. Studied in particular are moving-surface problems with continuous and discontinuous surface speeds, simple inflow–outflow problems and the impinging-jet problem within a circle. The analytical solutions at zero Reynolds number are given for the last two types of problem. Numerical results are obtained at various Reynolds numbers from the integral representation of the solution. At zero Reynolds number this approach involves a quadrature around the circumference of the cylinder. At other Reynolds numbers it involves an iterative–integral technique based on the use of the ‘clamped-plate’ biharmonic Green's function.

Magnetofluiddynamic flow with a pressure gradient and fluid injection

Abstract: The nonlinear partial differential equation of motion for an incompressible fluid flowing over a flat plate under the influence of a magnetic field and a pressure gradient, and with or without fluid injection (or ejection) through the plate is transformed to a nonlinear, third order ordinary differential equation by using a stream function and a similarity transformation. The necessary boundary conditions are developed for flow with and without fluid injection (or ejection), and an example is presented to illustrate the solution to the flow problem. The controlling equation reduces to the well known Falkner-Skan equation when the magnetic field is zero, and if additionally the pressure gradient is zero, the equation reduces to the Blasius equation.

Nonlinear steady incompressible lifting-surface analysis with wake roll-up

Abstract: The problem of lifting surfaces in steady incompressible flow is considered in terms of an integral equation relating the potential discontinuity on wing and wake to the normal derivative of the potential (normal wash) on the lifting surface. The integral equation is approximated by a system of linear algebraic equations obtained by dividing the surfaces into small quadrilateral elements and by assuming the potential discontinuity and the normal wash to be constant within each element. The wake geometry is obtained through iteration by satisfying the condition that the velocity be tangent to the surface of the wake and that the potential discontinuity be constant along the streamlines. Numerical results are in good agreement with existing ones

Water Waves in a Nonhomogeneous Incompressible Fluid.

Abstract: : After a brief discussion of some undesirable features of a number of different partial differential equations often employed in the existing literature on water waves, a relatively simple restricted theory is constructed by a direct approach which is particularly suited for applications to problems of fluid sheets. The rest of the paper is concerned with a derivation of a system of nonlinear differential equations (which may include the effects of gravity and surface tension) governing the two-dimensional motion of incompressible inviscid fluids for propagation of fairly long waves in a nonhomogeneous stream of water of variable initial depth, as well as some new results pertaining to hydraulic jumps. The latter includes an additional class of possible solutions not noted previously. (Author)

Hydrodynamics of deformable contiguous spherical shapes in an incompressible inviscid fluid

Abstract: An exact solution to the two-body interaction problem is presented for the case of spherical shapes moving in an incompressible and inviscid fluid. The spheres are assumed to translate in an arbitrary manner and to undergo radial deformation (or pulsation). The problem is formulated in terms of spherical harmonics and the force experienced by the spheres is obtained by employing the Lagally theorem. The expressions for the force are given as an infinite sum of coefficients which are found by solving an infinite set of linear equations. Three main geometries are considered, namely, two spheres exterior to each other, one sphere in the interior of the other and sphere in a rectangular channel. Numerical values for the added-mass coefficients as well as for the hydrodynamic forces are found for the case of rigid sphere moving toward or parallel to a rigid wall or a free surface, and a pulsating sphere in the proximity of these boundaries. Also given are numerical values for the transverse and the longitudinal addedmass coefficients for a sphere moving in a rectangular channel for different channel-blockage ratios.

Rayleigh-Taylor modes in constant-density incompressible fluids accelerated by radiation pressure

Abstract: The behavior of linear perturbations in an incompressible fluid undergoing acceleration by radiation pressure is examined A general formalism is developed, and explicit results are given for several examples in which the equilibrium density is a constant In that case, the sign of the derivative of the local radiative acceleration by the optical depth determines the stability of the short wavelength normal modes Long wavelength perturbations can be overstable independent of the shorter wavelength behavior When an external gravity is introduced, a transition, continuous in the strength of that external gravity, back to the ordinary Rayleigh–Taylor instability appears