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Fowlis, W. W.

Publications and source records attributed to Fowlis, W. W..

33 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The Numerical Studies Program for the Atmospheric General Circulation Experiment (AGCE) for Spacelab Flights

The atmospheric general circulation experiment (AGCE) numerical design for Spacelab flights was studied. A spherical baroclinic flow experiment which models the large scale circulations of the Earth's atmosphere was proposed. Gravity is simulated by a radial dielectric body force. The major objective of the AGCE is to study nonlinear baroclinic wave flows in spherical geometry. Numerical models must be developed which accurately predict the basic axisymmetric states and the stability of nonlinear baroclinic wave flows. A three dimensional, fully nonlinear, numerical model and the AGCE based on the complete set of equations is required. Progress in the AGCE numerical design studies program is reported.

Fowlis, W. W.↗
NASA NTRS1981

Overview

The creation of a spherical model in cylindrical geometry is discussed. The model requires a radial body force to simulate gravity. This force is achieved by dielectric effects on a liquid in the presence of a large voltage, but in the terrestrial laboratory it cannot be made large enough to overwhelm gravity. However, in an orbiting vehicle like Spacelab, this dielectric force will dominate. The behavior of a stripped down general circulation system (GCS) is a salient omission of GCM. It is suggested that the system will contribute to global weather and climate studies.

Fowlis, W. W.↗
NASA NTRS1981

The AGCE apparatus

The atmospheric general circulation experiment (AGCE) apparatus, an instrument to extend previous experimental work on baroclinic flows in cylindrical geometry to spherical geometry was proposed. The instrument must be flown in Spacelab to allow the radial dielectric body force which simulates gravity to be dominant. The essential configuration of the proposed apparatus is shown. Some preliminary values of dimensions and imposed conditions are included.

Fowlis, W. W.↗
NASA NTRS1981

Baroclinic instability of a rotating Hadley cell

The stability of a thin fluid layer between two rotating plates which are subjected to a horizontal temperature gradient is investigated. The solution for the stationary basic state is obtained in a closed form. It is pointed out that this solution identifies Ekman and thermal layers adjacent to the plates and interior temperature and velocity fields which are almost linear functions of height. The stability of that basic state with respect to infinitesimal zonal waves is then analyzed via the solution of the complete viscous linear equations for the perturbations. The character of the growth rates is found to be similar to those of the classical baroclinic waves. It is also found that the region of stability depends on the Prandtl number, the vertical stratification parameter, and both the meridional and zonal wavenumbers. The flow is generally unstable for small enough Ekman numbers and for Rossby numbers less than 10.

Antar, B. N.↗
NASA NTRS1980

Theoretical regime diagrams for thermally driven flows in a beta-plane channel in the presence of variable gravity

The effect of a power law gravity field on baroclinic instability is examined, with a focus on the case of inverse fifth power gravity, since this is the power law produced when terrestrial gravity is simulated in spherical geometry by a dielectric force. Growth rates are obtained of unstable normal modes as a function of parameters of the problem by solving a second order differential equation numerically. It is concluded that over the range of parameter space explored, there is no significant change in the character of theoretical regime diagrams if the vertically averaged gravity is used as parameter.

Geisler, J. E.↗
NASA NTRS1980

Eigenvalues of a baroclinic stability problem with Ekman damping

An analytical solution is presented for the baroclinic stability problem of a Boussinesq fluid in a beta-plane channel with Ekman suction boundary conditions. All of the modes, stable and unstable, belonging to this problem are identified. It is found that an unstable mode exists for only a certain range of values of the Burger number. The value of the Burger number at the upper limit of this range increases as the Ekman number decreases. Beyond this upper limit only a damped mode exists. It is also found that this transition in parameter space from the unstable to the stable mode occurs in a discontinuous manner.

Antar, B. N.↗
NASA NTRS1980

Numerical study of baroclinic instability

The effect of a power law gravity field on baroclinic instability is examined with emphasis on the case of inverse fifth power gravity, since this is the power law produced when terrestrial gravity is simulated in spherical geometry by electrostatic means. Growth rates of unstable normal modes were obtained as a function of parameters of the problem by solving a second order differential equation numerically. Results are compared with those from an earlier study where gravity was a constant. The conclusion is that, over the range of parameter space explored here, there is no significant change in the character of theoretical regime diagrams if the vertically averaged gravity is used as a parameter.

Geisler, J. E.↗
NASA NTRS1980

Baroclinic instability with variable static stability - A design study for a spherical atmospheric model experiment

The effect of a radially-variable, dielectric body force, analogous to gravity on baroclinic instability for the design of a spherical, synoptic-scale, atmospheric model experiment in a Spacelab flight is investigated. Exact solutions are examined for quasi-geostrophic baroclinic instability in which the rotational Froude number is a linear function of the height. Flow in a rotating rectilinear channel with a vertically variable body force without horizontal shear of the basic state is also discussed.

Giere, A. C.↗
NASA NTRS1979

The wave structures of the Eady model of baroclinic instability

By solving the linear quasi-geostrophic set of equations pertinent to the Eady model, the complex eigenvalues and the eigenfunctions are obtained. The propagation speed and the growth rate are computed. Quantitative information is provided about the wave structures for several unstable models, a marginally stable mode, and a stable mode. The peculiarities concerning the amplitude and the phase variations of the waves are noted as the wavenumber varies from the unstable region to the stable region. Physical interpretations of the interrelationships among the dynamical variables are given, with a view toward revealing important aspects of the energy transfer from the basic state to the growing waves.

Hyun, J. M.↗
NASA NTRS1979

Theoretical regime diagrams for thermally driven flows in a beta-plane channel

It is noted that thermally driven flows in rotating laboratory containers with cylindrical geometry can be axially symmetric or wavelike depending on the experimental parameters. In anticipation that rotating fluid experiments might soon be done in spherical shell geometry, Barcilon's model has been extended to a beta-plane channel in order to gain a rough understanding of the effects of rotating spherical geometry. An incompressible fluid version of the Charney (1947) model of baroclinic instability, modified to include Ekman pumping at rigid horizontal boundaries is used. With this model, stability boundaries are mapped out for individual zonal wavenumbers in the parameter space used by Barcilon.

Geisler, J. E.↗
NASA NTRS1979

Remote optical techniques for liquid flow and temperature measurement for Spacelab experiments

Three nonintrusive measurement techniques for Spacelab experiments are investigated. In the photochromic dye technique, a small amount of dye is dissolved in a low viscosity silicone oil and dye streaks are produced upon exposure to a UV source; the movement of the streaks reveals the flow. A laser Doppler dual-scatter system is being developed for low flow speed measurement; an accuracy of a few percent has been demonstrated for flows of a few millimeters per second. A double-grid schlieren system is being developed for temperature measurement; the optical arrangement is such that an image of a Ronchi ruling is superposed on the original ruling, giving a uniform gray field of view.

Fowlis, W. W.↗
NASA NTRS1978

The effects of curvature and viscosity on baroclinic instability: A two-layer model

A linear stability analysis of a baroclinic zonal current contained between two parallel rigid boundaries is presented. Curvature is included by performing the analysis on a beta b-plane and viscosity by allowing for the effects of Ekman layers on the rigid boundaries. A two-layer model is used. This calculation was carried out to assist in the design of a spherical model of the general circulation of the earth's atmosphere for Spacelab. In the low-gravity environment on an orbiting vehicle, a dominant radial dielectric body force, analogous to planetary gravity, can be achieved over a volume of liquid held between two concentric spheres. The results show the Eady short wavelength cutoff, and long wavelength cutoffs due to Ekman damping and curvature.

Fowlis, W. W.↗
NASA NTRS1978

Numerical solutions and laser-Doppler measurements of spin-up

The spin-up flow in a cylinder of homogeneous fluid has been examined both experimentally and numerically. A series of laser-Doppler measurements was made of the zonal flow over a range of Ekman numbers and Rossby numbers at various locations in the interior of the flow. These measurements exceed previous ones in accuracy. The weak inertial modes excited by the impulsive start are detectable. The numerical simulations used the primitive equations in axisymmetric form and employed finite-difference techniques on both constant and variable grids. The number of grid points necessary to resolve the Ekman layers was determined. A thorough comparison of the simulations and the experimental measurements is made which includes the details of the amplitude and frequency of the inertial modes. Agreement to within the experimental tolerance is achieved. Analytical results for conditions identical to those in the experiments are not available but some similar linear and nonlinear theories are also compared with the experiments.

Warn-Varnas, A.↗
NASA NTRS1977

Geophysical fluid flow model experiments in spherical geometry

An experimental and theoretical program was undertaken to assist in the design of geophysical fluid flow model experiments for Spacelab. Two new nonintrusive measurement techniques were developed. A theoretical calculation was carried out to guide the design of a proposed atmospheric general circulation model experiment.

Fowlis, W. W.↗