Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session BV: Geophysical Flows II |
Hide Abstracts |
Chair: Daniel P. Lathrop, University of Maryland Room: Ballroom B |
Sunday, November 23, 2008 10:30AM - 10:43AM |
BV.00001: Large-eddy simulation of scalar transport over complex terrain Takenobu Michioka, Fotini Chow An atmospheric large-eddy simulation code has been applied to simulate scalar transport and dispersion from point source releases during a field campaign conducted near Mt. Tsukuba, Japan. The simulations use horizontal grid resolution as fine as 190m with six grid nesting levels to incorporate time-dependent meteorological forcing. The results show that predicted ground concentration values contain significant errors compared to measured values because the mesoscale wind typically contains a wind direction bias of a few dozen degrees. Comparisons of simulation results with observations of arc maximum concentrations, however, lie within acceptable error bounds. Additionally, the choice of lateral boundary condition update interval is found to not affect time-averaged quantities but to strongly affect the scalar transport. More frequent updates improve the simulated ground concentration values. In addition, results show that the computational mixing coefficient must be set to as small a value as possible to improve scalar dispersion predictions. [Preview Abstract] |
Sunday, November 23, 2008 10:43AM - 10:56AM |
BV.00002: Simultaneous Pressure and Stereoscopic PIV measurements of the flow around a wall-mounted cube in an Urban-type Boundary Layer Bruno Monnier, Paritosh Mokhasi, Dietmar Rempfer, Candace Wark An experimental investigation of the flow around a wall-mounted cube in an experimentally modeled thick atmospheric boundary layer will be presented. Simultaneous Stereoscopic PIV measurements around the cube and pressure measurements on its surface are combined to obtain the 3D velocity field resolved both in space and time using a combination of the method of proper orthogonal decomposition and nonlinear Kalman filters. Mean velocity field, turbulence statistics and coherent structure identification tools are presented while the feasibility of extraction of time dependent data is investigated. [Preview Abstract] |
Sunday, November 23, 2008 10:56AM - 11:09AM |
BV.00003: Interactions Between a Turbulent Boundary Layer and a Wind Turbine Array Part 1: Inflow Conditioning and Experiment Characterization Jose Lebron, Raul Bayoan Cal, Luciano Castillo, Charles Meneveau A rough-wall turbulent boundary layer is created in a wind tunnel to replicate atmospheric turbulent boundary layer (ATBL) conditions and to study the interaction between the ATBL and an array of wind turbines. An active grid, vertical strakes and surface roughness are combined to create mean velocity and Reynolds stresses profiles that resemble those of an ATBL, as determined using thermal anemometry measurements. Wind-turbine models, scaled down 1000 times from real life length scales, use three bladed rotors with a diameter D = 12cm. Rotor blades are twisted 1.1 degrees per cm. Stereo-PIV measurements performed downstream of the wind turbine array show that the recovery of the wake occurs faster in this study than in many previous investigations, in which the incoming flow was typically less turbulent or representative of an array of wind- turbines. [Preview Abstract] |
Sunday, November 23, 2008 11:09AM - 11:22AM |
BV.00004: Interactions Between a Turbulent Boundary Layer and a Wind Turbine Array: Part 2. Turbulence and Periodic Motion Analysis Raul Bayoan Cal, Jose Lebron, Luciano Castillo, Charles Meneveau Stereo-particle image velocimetry (SPIV) measurements of flow structure in the wake of a three-by-three wind turbine (WT) array immersed in a rough-wall turbulent boundary layer are carried out. The aim of the measurements is to understand the complex interactions between the WT wakes and the boundary layer. In particular, a triple decomposition is performed separating the data into mean flow, periodic phase-averaged velocity fields, and Reynolds stresses. The 120 degree interval between blades of the three-bladed rotor is divided into 20-degree intervals and phase-locked SPIV measurements are performed. Deterministic stresses are evaluated and compared to the Reynolds stresses. Also, the effects of phase-dependent structures on the Reynolds stresses are quantified. [Preview Abstract] |
Sunday, November 23, 2008 11:22AM - 11:35AM |
BV.00005: LES of a Stratified Boundary Layer under an Oscillating Current Bishakhdatta Gayen, Sutanu Sarkar, John Taylor A numerical study based on large-eddy simulation (LES) is performed in the case of an oscillating tidal flow with a uniform ambient stratification. Here, the Reynolds number $Re_{\delta}=U_0\delta_s/\nu=1790$ ($U_0=$ maximum amplitude of the outer flow, $\delta_s= \sqrt{2 \nu/\omega}$ is the Stokes layer thickness, $\nu$ is the kinematic viscosity of the fluid and $\omega$ the angular frequency of the oscillatory current), and $N_{\infty}^2/\omega^2 = 500$ where $N_{\infty}$ is the buoyancy frequency of the overlying stratified layer. Turbulence appears at a tidal phase of approximately $\pi/4$ and is sustained throughout the deceleration phase ($\pi/2<\omega t_d<\pi$, $3\pi/2<\omega t_d<2\pi$). Production of turbulence is confined to the the wall region and, for stratified flow, in the mixed layer between the wall and the thermocline. For both the stratified and unstratified cases, there is a log layer over a significant extent of the tidal cycle. Our unstratified flow results are verified against the numerical simulations of Salon $et \; al$ (2007) %. $JFM, 2007$, vol 570, 253-296 and experimental data of Jensen $et \; al.$ (1987). %$JFM, 1987$, vol 206, 256-297. In the presence of stratification, the boundary layer height decreases substantially and the wall shear stress increases slightly with respect to the unstratified case. Stratification effects on boundary layer turbulence and on the thermal field including the formation and collapse of the thermocline will be discussed. [Preview Abstract] |
Sunday, November 23, 2008 11:35AM - 11:48AM |
BV.00006: Experimental measurements of lee wave interaction with wind shear, wakes, and boundary layers Michael Patterson, Colm Caulfield, Stuart Dalziel We present quantitative whole field measurements of the nonlinear internal wave field generated by a linearly stratified fluid that is perturbed by an idealized isolated ``mountain'' obstacle. We carried out experiments in a recirculating ``Kovasznay'' tank, which allows both the steady wave field to be quasi-stationary in the laboratory frame, and also for the effect of vertical variations in horizontal velocity to be studied straightforwardly. We observe critical layer absorption and total reflection at turning points, and we compare the effect of externally imposed shear with the behaviour associated with boundary layers both in the vicinity of the obstacle, (when the obstacle is located at the base of the tank) and at some distance (when the obstacle is located at the free surface). Post-processing of the experimental data using the Hilbert transform allows us to separate both the emitted outgoing and reflected incoming wave fields. Our results show that the the emission is a fundamentally nonlinear effect, with significant emission and absorption associated with the wake flow structure downstream of the obstacle. Our results suggest that wake effects may be responsible for the wave field observed downstream of many obstacles in atmospheric and oceanographic flows. [Preview Abstract] |
Sunday, November 23, 2008 11:48AM - 12:01PM |
BV.00007: Numerical Simulations of the Wake of a Maneuvering Body in a Stratified Fluid Kyle Brucker, Sutanu Sarkar The turbulent wake that exits behind a submersed body moving in
a stratified fluid is the subject of many experimental and
numerical investigations, no doubt due to its great importance to
the field of submersible vehicle design and operation. In
practice a submersible body moves at a constant speed, but
frequently experiences unsteady motion (i.e. acceleration,
deceleration, change in direction). However, this case has
received little attention and instead other idealized flows more
amenable to the current experimental and numerical tools
available are used as surrogate flows to make {\it inferences}
about characteristics of the wake.
The maneuvers are characterized by the ratio of the thrust and
drag coefficients and a geometric factor relating the thrust and
drag regions.
Results for the maneuvering wake include wake height, wake
width, peak defect velocity for $1 |
Sunday, November 23, 2008 12:01PM - 12:14PM |
BV.00008: ABSTRACT WITHDRAWN |
Sunday, November 23, 2008 12:14PM - 12:27PM |
BV.00009: LES of the flow field around a 45\r{ } wing-wall abutment in different scour conditions Filippo Bressan, Vincenzo Armenio, Francesco Ballio Scouring process around bridge abutment is one of the main causes leading to the hydraulic structure failure, thus the determination of the maximum scour depth assumes a central role. Resolved LES of the turbulent flow field around a 45\r{ } wing wall abutment are carried out for three main scouring conditions: Initial phase (flat bed), logarithmic phase of scouring and equilibrium scour depth. The bathymetry and the flow parameters are taken from data of a laboratory experiment. Mean flow field, secondary flows and turbulent quantities such as Reynolds stresses and turbulent kinetic energy are calculated and compared for the three cases. The purpose of this study is to understand how the statistics of the wall stresses change with the increase of the scour depth. Preliminary results indicate that the bottom stresses decrease as the scour hole increases and that the bed deforms itself in order to minimize the effect of the obstacle on the Bernoulli trinomial. The results of this research will help in finding new erosion models based on the knowledge of turbulence-bed interaction. [Preview Abstract] |
Sunday, November 23, 2008 12:27PM - 12:40PM |
BV.00010: A coupled immersed-boundary land-surface model for resolving atmospheric flows over complex terrain Katherine Lundquist, Fotini Chow, Julie Lundquist Atmospheric boundary layer flows are complicated by the presence of complex terrain which redirects mean flow and alters the structure of turbulence. Surface fluxes of heat and moisture provide additional forcing which induce secondary flows, or can dominate flow dynamics in cases with weak mean winds. Mesoscale models are increasingly used for high resolution simulations of complex terrain, but errors associated with terrain-following coordinates degrade the accuracy of the solution. Use of the immersed boundary method within mesoscale models allows explicit resolution of complex terrain; however, physics parameterizations of surface fluxes complicate treatment of the immersed boundary. We have implemented an immersed boundary method which is coupled to a land-surface model in the Weather Research and Forecasting (WRF) code. Realistic surface forcing is provided by atmospheric physics parameterizations, which are modified to include the effects of the immersed terrain. Validation is provided in the context of three-dimensional valley flow simulations. [Preview Abstract] |
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