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 NM: General Fluid Dynamics III |
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Chair: Michael Miksis, Northwestern University Room: Hilton Chicago PDR 1 |
Tuesday, November 22, 2005 11:01AM - 11:14AM |
NM.00001: The flow of a thin conducting film over a spinning disc in the presence of an electric field Chris Lawrence, Omar Kamal Matar The effect of an electric field on the flow of a thin conducting film over a spinning disc is studied. The electric field is imposed by applying a potential between the disc and an electrode overlying the film. The integral method and lubrication theory are used to derive a coupled set of evolution equations for the film thickness, radial flow rate and angular momentum. The results of our numerical simulations indicate that increasing the intensity of the electric field and decreasing the electrode separation exert a destabilizing effect leading to the formation of interfacial waves of larger amplitude than in the absence of electric effects. Spatial and temporal variations of the electric field also lead to complex film dynamics which give rise to sustained wave formation over a large fraction of the spinning disc. These results suggest that the application of an electric field can enhance the degree of wave-induced process intensification. [Preview Abstract] |
Tuesday, November 22, 2005 11:14AM - 11:27AM |
NM.00002: Theoretical modeling of turbulent flow in a fully-developed rotating square duct Zhaohui Qin, Richard Pletcher The theoretical modeling of flows in rotating duct can be traced back as early as to the 1970s. However, most researches focused on laminar flows. The current research tried to model the flow field in a turbulent rotating square duct. In a rotating duct, an Ekman layer comes into being near the side wall because of the balance between Coriolis force and pressure gradient. Near the stable wall, due to the inertial effect, a Stewartson layer appears. It is possible to solve the flow field close to the side and stable walls by either a similarity solution or an asymptotic solution. At the unstable wall, due to the turbulence and flow instability, a vortex shows up and has important impact on the total drag. The current research tries to give some clues to model the three layers. [Preview Abstract] |
Tuesday, November 22, 2005 11:27AM - 11:40AM |
NM.00003: Reduced Equations for Rapidly Rotating Convection in a Cylinder Michael Sprague, Keith Julien, Edgar Knobloch We discuss the derivation of a new reduced system of nonlinear PDEs for rapidly rotating Rayleigh-Benard convection (RBC) in a cylinder and examine its numerical solution. The equations are derived asymptotically in the limit of rapid rotation from the Boussinesq equations. Numerical simulation of the full Boussinesq equations for such flow is restricted due to the existence of fast-propagating inertial waves, and due to Ekman boundary layers that become increasingly thin with increased rotation rate. In the rapidly rotating limit, such boundary layers are passive, and are filtered-out in the reduced equations. Numerical simulation of a similar set of reduced equations for an unbounded layer has allowed thorough investigation of RBC in the limit of rapid rotation and for large Rayleigh numbers. Here, we limit our discussion to pattern formation at slightly critical Rayleigh numbers but under rapid rotation, for which there remain unexplained phenomena. [Preview Abstract] |
Tuesday, November 22, 2005 11:40AM - 11:53AM |
NM.00004: Reduced Equations for Rapidly Rotating Convection on the Tilted f-plane Keith Julien, Edgar Knobloch, Michael Sprague, Joseph Werne Non-Hydrostatic Quasi-Geostrophic Equations (NHQGE) are derived asymptotically in the limit of rapid rotation from the Navier-Stokes equations under the Boussinesq approximation. We consider the case where gravity and planetary rotation vectors are not aligned which requires a multiple-scales representation in a non-orthogonal coordinate system. We numerically investigate the solution to a reduced system of nonlinear PDEs for rapidly rotating convection: non-hydrostatic quasi-geostrophic equations (NHQGE). The resulting equations filter fast inertial waves and relax the need to resolve Ekman boundary layers. NHQGE are applicable to thermally forced flows characterized by thermal and vortical coherent structures that span the layer depth. We examine variation of heat transport as a function of scaled Rayleigh number. We also investigate the dynamics of the vortical structures and their effect on lateral mixing. [Preview Abstract] |
Tuesday, November 22, 2005 11:53AM - 12:06PM |
NM.00005: Direct numerical simulation of stably-stratified turbulent channel flows with strongly property changes Yoshinobu Yamamoto, Tomoaki Kunugi, Shin-ichi Satake In this study, Direct Numerical Simulations of stably- stratified turbulent channel flows were conducted to investigate strongly property change and buoyancy effects on turbulent structures and heat transfer. Fully-developed stably-stratified turbulent channel flows at CO$_2$ supercritical pressure (7.58MPa) were treated as the flow fields. Constant temperature conditions were considered as the thermal boundary conditions: top and bottom wall temperatures kept at 32.7 and 31.7 degrees, respectively. In this temperature range, thermal properties of CO$_2$ were strongly changed and have a sharp peek at 32.2 degree. At first, numerical investigation was carried out in case of passive scalar transport to evaluate the grid resolutions for thermal property change. Next, DNS database under forced convection conditions: Turbulent Richardson number (Ri) between 0 and 15, were constructed. As the results, in passive scalar case (Ri=0), effects of high- Pr fluid characteristic and property change on the budget of mean energy equation were remarkably appeared. The spanwise turbulent heat flux due to the property change and the high and low-speed streaky structures was dominant to energy equation budget near wall. In stable cases, the tendency of flow laminarization was observed due to the buoyancy, but its effects on turbulent statistics seem to be inactive compared with low-Pr fluid case in the same Ri condition. [Preview Abstract] |
Tuesday, November 22, 2005 12:06PM - 12:19PM |
NM.00006: Euler-alpha and vortex blob regularization of vortex sheet motion Monika Nitsche, Darryl Holm, Vakhtang Putkaradze The Euler-alpha and the vortex blob model are two different regularizations of incompressible ideal fluid flow. We apply both models to compute the motion of vortex sheets and compare the results. By certain measures, the Euler-alpha model is closer to the unregularized flow than the vortex blob model. The differences that result in vortex sheet linear stability properties and core dynamics of the spiral vortex sheet roll-up are discussed. [Preview Abstract] |
Tuesday, November 22, 2005 12:19PM - 12:32PM |
NM.00007: Interaction forces in bi-disperse particulate systems Xia Ma, Duan Zhang In many granular flow models, the average motion of two types of particles is described by two averaged momentum equations. The interactions between two types of particles are solely represented by the averaged interaction forces in the momentum equations. There are examples in the literature that regard the sum of the interaction forces in the two momentum equations as zero for reasons related to the action-and-reaction principle. Unfortunately, such application of the action-and-reaction principle is incorrect, because the interaction forces are averaged under different conditions. The interaction force for one type of particle is averaged under the condition that the corresponding spatial point is occupied by that type of particle. A given spatial point cannot be occupied by two types of particles at the same time. In this presentation, we will show that the sum of the averaged interaction forces is a divergence of a stress tensor. Numerical simulations are performed to investigate the averaged interaction forces acting on two different sizes of particles undergoing relative motion. The stresses and average interaction forces between two different types of particles are computed. [Preview Abstract] |
Tuesday, November 22, 2005 12:32PM - 12:45PM |
NM.00008: WITHDRAWN: Force fluctuations in a 3-dimensional, dense, granular flow Efrosyni Seitaridou, Ellen Keene, Nalini Easwar, Narayanan Menon We have made measurements of the force normal to the wall of a 3-dimensional, gravity-driven, granular flow down a vertical cylindrical pipe. The force measurements were made at four locations, each over an area comparable to the size of a grain. The flow velocity is controlled by varying the size of the outlet at the bottom of the pipe. As the outlet is constricted, we monitor the continuous evolution in the mechanism of momentum transfer to the wall from short-lived, collisional interactions to enduring, frictional contacts. As in static granular media, and in some slow granular flows, the distributions of forces are broad, however, unlike previously studied situations, the distributions are not always exponential. We also report on the spatial and temporal correlations in the force and velocity in order to test the robustness of the observation in 2-dimensional flows that the jamming of the flow is due to transient force- bearing structures that span the flow. [Preview Abstract] |
Tuesday, November 22, 2005 12:45PM - 12:58PM |
NM.00009: Microbubbling in microfluidics using Flow Focusing for moderate-high Reynolds. Juan M. Fernandez, Alfonso M. Ganan-Calvo A bubbly flow in a microfluidic substrate shows distinctive features which makes it attractive for a variety of important applications. Firstly, the liquid-gas surface per unit liquid volume is very high, and therefore the forces originated at the liquid-gas interfaces greatly affect the whole liquid bulk flow. Secondly, microfluidic geometries generally impose narrow passages which create regions where strong convective accelerations take place for moderate-high Reynolds flows. In particular, strong convective accelerations can be locally enhanced using Flow Focusing geometrical configurations, increasingly used in microfluidics (axisymmetric, planar, etc.). These combined effects cause strong local instabilities in the flow leading to a robust and perfectly controllable microbubbling with a remarkable regularity and characteristic frequencies in the KHz-MHz range, when using Flow Focusing and moderate-high Reynolds liquid flow. The size of the microbubbles produced spans from the micrometric to the nanometric range. The intriguing physics behind these microbubbling phenomena can be globally described by scaling laws which have been extensively compared with experiments, showing a remarkable agreement. These scaling laws are fundamentally dictated by the microfluidic geometry used, and by the gas to liquid flow rates ratio. Their wide-range applications will be outlined. [Preview Abstract] |
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