Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session LO: Industrial Applications and Material Processing Flows |
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Chair: Dana Dabiri, University of Washington Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 11 |
Tuesday, November 21, 2006 8:00AM - 8:13AM |
LO.00001: Mathematical and Numerical Modelling of an Axisymmetric Valve Richard Gibbs, Jonathan Kobine Current models for accurate flowrate control valves are largely empirical. Our valve device allows pressure-driven flow through the passage formed between two concentric truncated cones; the flow is controlled by varying the relative vertical displacement of the two cones. For converging steady laminar flow of an incompressible Newtonian fluid we develop a viscous flow solution for the annular channel region between the two cones, assuming that the channel is narrow. Inviscid flow is assumed in the following conical chamber. The resulting analytical model essentially captures the discharge as a function of valve opening, from comparison with finite element simulations, for low Reynolds numbers ($Re<100$) and cone apex half-angles from $30$ to $80^{\circ}$. For smaller cone angles the main difference between the model and the simulations occurs when the depth of the conical chamber is such that viscous effects must also be included in this region. We also give an assessment of the effect of rotation of the inner cone, which sets up an additional pressure gradient across the device, as a means of flow control. [Preview Abstract] |
Tuesday, November 21, 2006 8:13AM - 8:26AM |
LO.00002: The flow in an underfloor plenum. A comparison of experiment and simulation. Jong Keun Yu, Paul Linden In underfloor air distribution (UFAD) systems cool air is introduced through diffusers placed in a raised floor. Air is delivered to the diffusers after circulating in the plenum. The heat transfer across the floor heats the air in the plenum, which results in temperature variations at the diffusers. Consequently, there can be thermal discomfort of occupants and loss of energy efficiency of the system. The flows in an underfloor plenum with multi-supply air inlets are investigated by means of laboratory experiments using particle image velocimetry (PIV) and by numerical simulations (FLUENT 6.22, FLUENT Inc.). The inhibition of vertical motions induced by the small aspect ratio of vertical length scale to horizontal length scale of the plenum, implies that two-dimensional flow dynamics characterize the flow. The experimental and numerical results strongly support the relevance of these two-dimensional flow dynamics. Self-organization processes are observed which lead to the formation of long-lived coherent flow structures, resulting from inverse energy cascade in the two-dimensional turbulent flow due to the absence of vortex stretching and twisting. Furthermore, we analyze thermal performances of the inlet configurations by three dimensional numerical simulations. [Preview Abstract] |
Tuesday, November 21, 2006 8:26AM - 8:39AM |
LO.00003: Effect of Various Parameters on Evolution of 2D Free Jets and their Associated Entrainment Rates Mazyar Amin, Dana Dabiri, Homayun Navaz Refrigerated vertical display cases are extensively used in supermarkets and grocery stores. Cold air is supplied vertically across the open face of the display case from the top, creating a cold air curtain acting as a barrier to separate the cold air within the case from the warm ambient air. Typically, 70-80{\%} of the load on these vertical display cases is due to cooling of infiltrated warm ambient air. Our goal is to understand parameters affecting warm air infiltration into the case so as to minimize the cooling load. Towards this end, steady state behavior of 2D vertical air jets at Reynolds numbers 2,000 to 10,000 with low and high turbulence intensities (0{\%} {\&}10{\%}) at the nozzle exit are experimentally and computationally investigated both within a quiescent ambient and next to an open cavity. Four different velocity profile shapes (top-hat, parabola, skewed parabola and linear) at the jet exit are also studied to determine profile effects on the evolution of and entrainment into the jet. Results will be presented to show the effect of these parameters on the total entrainment into the jet, as well as the variation of entrainment across the jet at different downstream locations. The results of this work can help better understand how to design air curtains as a buffer to minimize infiltration into open refrigerated vertical display cases. [Preview Abstract] |
Tuesday, November 21, 2006 8:39AM - 8:52AM |
LO.00004: Study on Characteristics of Wind-Induced Inflow and Outflow through a Single Opening in a building using LES {\&} DES Takamasa Hasama, Shinsuke Kato, Ryozo Ooka In order to investigate wind-induced flow properties through a single opening, large-eddy simulations (LES) are performed on ventilated air through the single opening of a room. In this flowfield, the outdoor air flows parallel to the wall and to the opening, and the room airflow is induced by the outdoor flow through the opening. Both the outdoor and indoor airflows are simultaneously simulated. Firstly, the dependency of the induced room airflow to the shape of the opening is investigated (by changing the shape of the opening). Secondly, the distributions of mean and turbulent variables at the boundary plane of the opening are investigated. And thirdly, Detached-eddy simulations (DES) are performed on the same flowfield to examine the applicability of DES to building ventilation analysis. It is clarified that the shape of the opening and the resultant mixing layer thickness developed along the opening boundary plane affect the characteristics of the air exchange rate and the feature of the room's airflow. In the case of a longer opening, the change in air exchange characteristics is apparent. And, DES over-estimates the sub-grid scale (SGS) viscosity in the LES region, but the difference in room mean property between both cases is low. [Preview Abstract] |
Tuesday, November 21, 2006 8:52AM - 9:05AM |
LO.00005: Hydrodynamic analysis of field data acquired during well drilling with aerated fluid. Ruben Lopez, Antonio Lopez, Maria Herrera During conventional well drilling the circulating system consists as follow, the drilling fluid is pumped downward into the drilling pipe until the bottom of the open hole then it flows through the drill bit, and at this point formation cuttings are incorporated to the circulating fluid and carried upward to the surface. The mixture returns up to the surface by an annular flow area. However, throughout drilling operations with aerated fluid, the drilling fluid used is composed by gas and an oil-based mud. In consequence, it involves a multiphase flow hydrodynamic analysis. For achieving this, it is necessary a better understood of the flow mechanisms in drilling rig and the operational technique. Therefore, it was carried out a multiphase conservative model that includes three mass equations and a momentum equation. The mathematical model is solved by numerical conservative schemes. The real operational conditions are fed to conservative model and the results are matched up to field measurements in several oil wells. Mainly, flow rates, drilling rate, well and tool geometries are data to estimate the profiles of pressure, mixture density, equivalent circulating density, gas fraction and solid carrying capacity. Even though the problem is very complex, the model describes, properly, the hydrodynamics of drilling techniques applied at oil fields. It is supported by the field data acquired and study cases. [Preview Abstract] |
Tuesday, November 21, 2006 9:05AM - 9:18AM |
LO.00006: Numerical study of coupled transfer of heat and mass between air and water inside a geothermal water cooling tower Mohamed Mehdi Bassem, Karim Bourouni, Mohamed Thameur Chaibi In the south of Tunisia, geothermal water is used to irrigate cultures. Since its temperature is very high (70\r{ }C), geothermal water is cooled by cooling towers. These towers are sized empirically and present many operating problems such as excessive energy consumption, big loss of vapour and low cooling efficiency. The aim of our work is modelling the coupled heat and mass transfer between air and water inside the cooling tower. The most important results obtained are that the evaporative potential is dominating the convective one in the cooling process. That's why the cooling is more efficient in summer than in hibernal period when humidity of ambient air reaches high values. In other hand, the negative convective phenomenon is illustrated. In fact, at the bottom of the tower, water temperature reaches the air one; the two fluids begin to cooling simultaneously. Air is cooled by convection and water by evaporation. We demonstrate also that there is no point in putting fans in working during cold weather. We studied also the effect of the variation of heat transfer coefficient on the efficiency of cooling. [Preview Abstract] |
Tuesday, November 21, 2006 9:18AM - 9:31AM |
LO.00007: Analysis of Net Engagement with a Towcable Katherine Mangum, Richard Knutson, Stephen Ebner The Naval Surface Warfare Center, Carderock Division conducted a test in the deep water David Taylor Model Basin (DTMB) in September of 2006. The objective of the test was to evaluate the interaction of a towcable with drift nets and with longlines. Entanglement is a major problem in military and commercial applications, both with ship towed systems and with helicopter towed systems. A tenth scale model of nets and target towcable were designed and fabricated to allow proper froude scaling. Simulation was done to predict net behavior at various end drag conditions, thus simulating different typical net lengths. Other variables evaluated were cable scope, tow speed, net angle with respect to towcable at point of engagement, and centered versus off center point of contact. After engagement studies, a sample net cutter was towed to examine probability of success. Visual and quantitative data were compared for all cases to evaluate the net simulations. [Preview Abstract] |
Tuesday, November 21, 2006 9:31AM - 9:44AM |
LO.00008: ABSTRACT WITHDRAWN |
Tuesday, November 21, 2006 9:44AM - 9:57AM |
LO.00009: Experimental Study of the Mixing Field Induced By A Rotating Flat Plate in a Cylinder Douglas Bohl In this work a flat rectangular plate is rotated along its long axis and parallel to the z-axis of a circular cylinder. The blade position is varied with respect to the cylinder wall to allow investigation of the effect of the no slip boundary on the flow structure and mixing field. The cylinder is filled with four Newtonian fluids with different viscosities that allow a Reynolds number range of 0.005 -- 7800 to be investigated. Particle Image Velocimetry is used to measure the velocity in the plane perpendicular to the rotation of the plate (i.e. in the r-theta plane of the cylinder). The velocity field is post processed to provide the vorticity and local stretch rates (which can be correlated with the mixing efficiency). Results show that a vortex is formed at the tip of the mixing blade. The magnitude of this vorticity increases as the gap between the blade and the wall is decreased. The peak local stretch rate increases exponentially as the gap between the blade and the wall is decreased. The results also indicate that the peak local stretch rate is a linear function of the log of the Reynolds number. [Preview Abstract] |
Tuesday, November 21, 2006 9:57AM - 10:10AM |
LO.00010: Particle Sorting by Aerodynamic Vectoring Zachary Humes, Barton Smith An experimental and numerical demonstration of a new, non-contact particle sorting technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows to sharply turn a 2D, particle-laden jet. As the jet is turned, particles present in the flow experience a resultant force, dependent upon their size and due to the combined effects of pressure, inertia, and drag. Since the balance of these forces determines the particle's trajectory, turning the flow leads to a separation of particles downstream. This simple, low-pressure-drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices.~ AVPS is experimentally demonstrated using a rectangular air jet. Particle size and trajectory are measured using the Shadowgraphy method.~ Numerical simulations are performed using the commercial CFD solver FLUENT to calculate the 2D turbulent vectored jet flow field using a RANS approach. Examination of the mean and the standard deviation of measured and computed particle trajectories is used to determine the range of particle sizes that can be effectively sorted using AVPS. [Preview Abstract] |
Tuesday, November 21, 2006 10:10AM - 10:23AM |
LO.00011: The Role of Thermoelectromagnetic Convection in Semiconductor Crystal Growth Brent Houchens Semiconductors are often grown in magnetic fields to damp or control the melt motion. In high magnetic fields, a nearly quiescent melt can be achieved. The leading order electromagnetic damping (by way of the Lorentz body force) increases with the square of the strength of the applied magnetic field. However, experimentalists discovered that increasing the magnetic field strength past a certain threshold caused the melt to transition from a nearly quiescent state to an oscillatory flow. It was hypothesized that second order thermoelectric currents could be responsible for the oscillatory flow. These Seebeck electromotive currents are generated at the solidification front where gradients of thermoelectric power and temperature are not parallel. This additional electric current also interacts with the applied magnetic field, providing a new flow mechanism, thermoelectromagnetic convection (TEMC). Here, the basic principles of TEMC will be discussed, and results from a prototypical model will be presented. [Preview Abstract] |
Tuesday, November 21, 2006 10:23AM - 10:36AM |
LO.00012: Development and Application of an Improved PIV System for Turbomachinery Applications Dave Gebbie, Steve Gorrell, Jordi Estevadeordal The flow field due to blade-row interactions in turbomachinery includes phenomena producing unsteadiness and losses that affect the turbomachine performance. PIV techniques have been very useful in the past for identifying and understanding these phenomena that include shocks, wakes and vortices. Most successful PIV approaches have relied on optical probes inserted in modified stator blades or in the flow field to deliver the laser sheet inside the various internal regions of the blade-rows. These approaches have important drawbacks, such as probe intrusiveness, shadows in areas of interest and expensive glass windows. A new design that focuses on minimizing intrusiveness, effective laser delivery inside all regions of interest, and economical receiving windows is presented. The design of the PIV blades allows for small optics to be embedded inside with the location, size, and shapes determined through analysis of the flow path and CFD techniques. The optical performance of the design is tested in full scale models. An economical and fast technique based on rapid machining of transparent acrylic material for receiving windows is also presented. The design of the system is outlined and results from application to a transonic axial compressor presented. [Preview Abstract] |
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