Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session BR: Turbulent Boundary Layers: Thermal Effects |
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Chair: William George, Chalmers University of Technology Room: Hilton Chicago Stevens 3 |
Sunday, November 20, 2005 10:56AM - 11:09AM |
BR.00001: Temperature Scales for Thermal Turbulent Boundary Layers Xia Wang, Luciano Castillo, Guillermo Araya An inner temperature length scale was assumed based on the analogy between the momentum and the thermal transport for a forced convection turbulent boundary layer. Subsequently, a temperature scale was obtained from the inner energy equation using the theory of similarity analysis. These scales were firstly proposed by Wang and Castillo (2003), which was shown to successfully remove the effects from upstream conditions, pressure gradients and the Peclet number on the downstream flow. However, there are some other important factors such as the effects of various Prandtl numbers and various wall conditions which affect the behavior of the boundary layer flow and have not been studied yet. In this investigation, we will improve both the length and temperature scales and verify them using the experimental or numerical simulation results with various Prandtl numbers and wall conditions. All these effects are expected to be removed when the temperature profiles are normalized using the scales proposed here. Meanwhile, the methodology used to derive the scales will be explored to investigate the thermal boundary layer flow subject to the nature convection heat transfer or the combined convection heat transfer. [Preview Abstract] |
Sunday, November 20, 2005 11:09AM - 11:22AM |
BR.00002: Nearly Free Convection in Thermally Stratified Boundary Layers Roddam Narasimha Thermally stratified boundary layers have generally been handled through Monin-Obukhov theory, although there has been considerable discussion about the free convection limit of this theory. Based on two atmospheric boundary layer experiments, one at Jodhpur in India and the other in Oklahoma, US, it is shown here that if the mean wind is sufficiently low, the drag varies linearly with wind while the heat flux continues to be governed by the free convection law. These characteristics define what may be called the `weakly forced convection' sub-regime within the broader regime of mixed convection. To make scaling arguments in this sub-regime, it is shown that it is useful to adopt the heat flux, rather than the wall stress (equivalently friction velocity) as Monin-Obukhov theory does. Several candidates for a heat-flux velocity scale are considered, and their relative merits assessed. These arguments lead to novel definitions of drag and heat transfer coefficients that are independent of wind speed. [Preview Abstract] |
Sunday, November 20, 2005 11:22AM - 11:35AM |
BR.00003: Universal Realizable Reynolds Stress Model for Multiphase Fluids Charles Petty, Andre Benard, Karuna Koppula The ability to predict the low-order statistical properties of single-phase and multiphase turbulent flows is critical for engineering processes such as mixing and separation of immiscible phases. Although instantaneous phase-averaged equations have been successfully developed over the past thirty years for multiphase fluids, the ensemble-averaged equations for turbulent flows are statistically unclosed. Many researchers use a multiphase eddy viscosity model to relate the Reynolds stress to the local mean strain rate, but this approach is unsuitable for processes where phase separation and mixing by local pressure differences is a significant phenomena. A new closure for the Reynolds stress that is realizable for a wide class of turbulent flows yields a non-linear algebraic relationship between the turbulent momentum flux and a non-negative, symmetric dyadic-valued operator that depends on the mean velocity gradient and a relaxation time associated with the local space-time structure of the turbulence. Benchmark experimental and computational data for single-phase fluids are used to determine the closure parameters in the theory. The presentation will summarize the new approach and its extension to multiphase turbulent flows. [Preview Abstract] |
Sunday, November 20, 2005 11:35AM - 11:48AM |
BR.00004: Large Eddy Simulation study of the development of finite-channel lock-release currents at high Grashof numbers Seng-Keat Ooi, George Constantinescu, Larry Weber Lock-exchange gravity current flows produced by the instantaneous release of a heavy fluid are investigated using 3-D well resolved Large Eddy Simulation simulations at Grashof numbers up to 8*10$^{9}$. It is found the 3-D simulations correctly predict a constant front velocity over the initial slumping phase and a front speed decrease proportional to t$^{-1/3}$ (the time t is measured from the release) over the inviscid phase, in agreement with theory. The evolution of the current in the simulations is found to be similar to that observed experimentally by Hacker et al. (1996). The effect of the dynamic LES model on the solutions is discussed. The energy budget of the current is discussed and the contribution of the turbulent dissipation to the total dissipation is analyzed. The limitations of less expensive 2D simulations are discussed; in particular their failure to correctly predict the spatio-temporal distributions of the bed shear stresses which is important in determining the amount of sediment the gravity current can entrain in the case in advances of a loose bed. [Preview Abstract] |
Sunday, November 20, 2005 11:48AM - 12:01PM |
BR.00005: Remote sensing from space of turbulence produced by a submerged municipal wastewater outfall Pak Tao Leung, Hartmut Prandke, Valery Bondur, Norris Keeler, Carl Gibson Satellite imagery of sea surface brightness reveals narrow wavenumber spectral anomalies at distances up to 20 km from the diffuser (1). Three international expeditions in 2002, 2003 and 2004 monitored receiving waters with an array of hydrographic and turbulence microstructure sensors in anomaly and ambient regions. Drifters set near the 40-50 m trapping depth of the effluent, as well as ADCP measurements, show complex currents (tides, lee eddies, freshwater run-off). Mean turbulence parameters for $\sim $ 10$^{4}$ microstructure patches (3) in the anomaly and ambient regions have been analyzed to understand the complex stratified turbulence processes. The results point to different possible mechanisms: internal waves produced by the outfall turbulence and/or buoyancy effects, fossils of the outfall turbulence, secondary and ambient internal waves (2). See related information at http://www-acs.ucsd.edu/$\sim$ir118 1. Keeler, R. N., V. G. Bondur, and C. H. Gibson (2005). Optical satellite imagery detection {\ldots} , Geophys. Res. Lett., 32, L12610 2. Leung, P. T., and C. H. Gibson (2004). Turbulence and fossil turbulence in oceans and lakes, Chin. J. Oceanol. Limnol., 22, 1 3. Prandke, H. and A. Stips (1992). A model of Baltic thermocline turbulence patches {\ldots} , Cont. Shelf Res.,12, 643 [Preview Abstract] |
Sunday, November 20, 2005 12:01PM - 12:14PM |
BR.00006: Aircraft Boundary-layer Measurements in the Gulf of Tehuantepec Carl Friehe, Djamal Khelif, W.K. Melville Airborne flux, meteorological, and wave measurements were made from the NSF/NCAR EC130Q aircraft in the Gulf of Tehuantepec under strong boundary-layer gap winds up to 25 m/sec at 33 m height. Statistics of flux estimates were obtained from multiple 33-m tracks flown under reasonably stationary and homogeneous conditions. Flux divergence was obtained from stack patterns flown at various distances from shore. Tracks flown at 33 m between the stacks provided the pressure gradient and advection terms in the momentum balance. Near shore, flux divergence was important and approximately balanced by the pressure gradient and advective terms; off-shore (400 km), divergence was small and again approximately in balance with the other two terms. Data from dropsondes and the Scanning Aerosol Backscatter LIDAR (SABL) revealed that the internal boundary layer initially thins off-shore as the gap wind field spreads horizontally, and then thickens due to turbulent mixing and possible hydraulic effects. Supported by NSF Division of Ocean Sciences. [Preview Abstract] |
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