Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session QX: Industrial Applications II |
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Chair: Jerry Tessendorf, Rhythm and Hues Studios Room: Hyatt Regency Long Beach Regency D |
Tuesday, November 23, 2010 12:50PM - 1:03PM |
QX.00001: Numerical investigation for design and critical performance evaluation of a horizontal axis hydrokinetic turbine Suchi Subhra Mukherji, Arindam Banerjee We will discuss findings from our numerical investigation on the hydrodynamic performance of horizontal axis hydrokinetic turbines (HAHkT) under different turbine geometries and flow conditions. Hydrokinetic turbines are a class of zero-head hydropower systems which utilizes kinetic energy of flowing water to drive a generator. However, such turbines very often suffer from low efficiency which is primarily controlled by tip-speed ratio, solidity, angle of attack and number of blades. A detailed CFD study was performed using two-dimensional and three dimensional numerical models to examine the effect of each of these parameters on the performance of small HAHkTs having power capacities $\le $ 10 kW. The two-dimensional numerical results provide an optimum angle of attack that maximizes the lift as well as lift to drag ratio yielding maximum power output. However three-dimensional numerical studies estimate optimum turbine solidity and blade numbers that produces maximum power coefficient at a given tip speed ratio. In addition, simulations were also performed to observe the axial velocity deficit at the turbine rotor downstream for different tip-speed ratios to obtain both qualitative and quantitative details about stall delay phenomena and the energy loss suffered by the turbine under ambient flow condition. [Preview Abstract] |
Tuesday, November 23, 2010 1:03PM - 1:16PM |
QX.00002: Ion Wind Generation and its Application to Cooling Device Bumchang Kim, Sanghyun Lee, You Seop Lee, Kwan Hyoung Kang Ion wind generation (IWG) has a long history in the field of electrohydrodynamics (EHD). The application of IWG to cooling devices has drawn much attention, mainly because of its extremely low level of acoustic noise emission, compared to the conventional mechanical fan. In this work, we performed a parametric study for geometrical and electrical configurations, electrode materials, and surrounding media such as air, nitrogen, and argon. Wind velocity and volume flow rate are measured with regard to power efficiency, operational voltages, and polarities such as DC+, DC-, and AC. The effect of electrode materials and the surrounding media on the morphological changes of the electrode surface is discussed. This study envisions that the IWG could be a promising cooling mechanism, although there are several issues such as safety and maintenance that need to be addressed. [Preview Abstract] |
Tuesday, November 23, 2010 1:16PM - 1:29PM |
QX.00003: Numerical Simulations of a Roof-Top Wind Turbine Shahab Moayedian, Hamid Rahai Unsteady numerical simulations of a high efficiency roof-top wind turbine have been performed. The wind turbine cross section design was based on geometrical optimization study of Rahai and Hefazi for increasing contributions of the lift force to the torque, resulting in significant improvements in the performance of a vertical axis wind turbine. The wind turbine was 30 cm in diameter and 75 cm length, with 45 cm diameter end-plates, placed in the spanwise direction above a 26 degree slanted roof at 20 percent from the roof's highest elevation and one turbine diameter away from the roof surface. The approaching wind velocity was 30 m/sec and the wind turbine RPM was 233. Results indicate nearly 20 percent improvements in the power output, when compared with the corresponding results for a free standing wind turbine. However, the wind turbine operation imposes oscillatory stress on the roof, which could results in structural vibration and damage and noise generation. [Preview Abstract] |
Tuesday, November 23, 2010 1:29PM - 1:42PM |
QX.00004: Evaluating Contributions of Turbulent kinetic Energy Fluxes To Streamtube Analysis of Wind Turbines in an Array Jose Lebron, Luciano Castillo, Charles Meneveau Ever since the streamtube concept was introduced by Betz in 1926, the analysis have been widely used for describing the flow upstream and downstream of wind turbines. The analysis is used to relate power output to the differences of kinetic energy fluxes at the inlet and outlet of the streamtube. However, the classical analysis assumes ideal flow, neglecting, in particular effects of turbulence. For applications to large arrays of wind turbines placed in the highly turbulent atmospheric boundary layer, these assumptions do not hold. In the current study, PIV data taken in a wind tunnel 3x3 turbine array experiment (Cal et al. 2010, J. Renewable and Sustainable Energy), is analyzed. The fluxes of turbulent kinetic energy at the streamtube control surfaces are computed in order to determine their overall impact and to better understand the energy exchange between the turbine and the Atmospheric Boundary Layer. [Preview Abstract] |
Tuesday, November 23, 2010 1:42PM - 1:55PM |
QX.00005: Numerical Modeling of Hydrokinetic Turbines and their Environmental Effects Teymour Javaherchi, Alberto Aliseda Energy extraction from ocean tides via hydrokinetic turbines has recently attracted scientists and engineers attention as a highly predictable source of renewable energy. However, since the most promising locations in terms of resources and proximity to the end users are in fragile estuarine ecosystems, numerous issues concerning the environmental impact of this technology need to be addressed a priori before large scale deployment. In this work we use numerical simulations to study the possible environmental effects of hydrokinetic turbines through their influence on physical flow variables such as pressure and velocity. The velocity deficit created in the turbulent wake of a turbine affects the settling of suspended sediment in the water column and can lead to deposition into artificial patterns that will alter the benthic ecosystem. On the other side of the spectrum, pressure fluctuation through turbine blades and in blade tip vortices can damage internal organs of marine species as they swim through the device, particularly for small juveniles that behave like Lagrangian trackers. We present sedimentation statistics to understand the sensitivity of this phenomena to turbine operating conditions and sediment properties. We also show pressure history for slightly buoyant Lagrangian particles moving through the turbine and correlations with damage thresholds obtained from laboratory experiments. [Preview Abstract] |
Tuesday, November 23, 2010 1:55PM - 2:08PM |
QX.00006: Hydrodynamic Performance of a Wave Energy Converter Yingchen Yang To harvest energy from ocean waves, a new wave energy converter (WEC) was proposed and tested in a wave tank. The WEC freely floats on the water surface and rides waves. It utilizes its wave-driven angular oscillation to convert the mechanical energy of waves into electricity. To gain the maximum possible angular oscillation of the WEC under specified wave conditions, both floatation of the WEC and wave interaction with the WEC play critical roles in a joint fashion. During the experiments, the submersion condition of the WEC and wave condition were varied. The results were analyzed in terms of the oscillation amplitude, stability, auto-orientation capability, and wave frequency dependency. [Preview Abstract] |
Tuesday, November 23, 2010 2:08PM - 2:21PM |
QX.00007: Energy extraction from flexible slender bodies Kiran Singh, Sebastien Michelin, Emmanuel de Langre Long slender structures such as underwater cables may develop instabilities that can lead to large amplitude oscillations, chaotic behaviour invariably leading to failure. Whilst the norm is to avoid such regimes, here we examine the converse problem of energy extraction from flexible slender bodies in a fluid. We derive the terms for this fluid-structure interaction problem paying specific attention to large-amplitude deflections in the small curvature limit. We use a local approach to model inviscid and viscous fluid dynamic contributions. We represent the structure as a bi-articulated cylindrical pendulum with stiffness and structural damping introduced discretely at the joints; the simple system thus has two degrees of freedom, $(\theta_1,\theta_2)$ with fixed-free boundary conditions. We solve the coupled system of second order in time non-linear ODEs and examine the response of this fourth order system, ${\mathbf{Y}}=\{\theta_1,\theta_2,\dot{\theta}_1,\dot{\theta}_2\}^T$. A key objective of this work is to examine the feasibility of energy extraction from such systems, represented by the structural damping term. In order to examine the parameter space for likely solutions, we quantify the associated energies and examine the related problem of stability. In particular, we are interested in seeking stable limit-cycle oscillations. Time permitting, we consider the flexible slender body response for specific cases. [Preview Abstract] |
Tuesday, November 23, 2010 2:21PM - 2:34PM |
QX.00008: On the flow around a hydrofoil close to a permeable wall Mats Nigam In the pulp and paper-making industry, pressurized screens are used to purify the pulp and to protect the wires on the paper machine. The appertures (slots or holes) on the screen are kept clean from fibers and shives by foils rotating close to the permeable surface. The leading-order theory of a ``wing in extreme ground effect'' has been modified to take into account the permeability of the screen-plate. Methods for predicting flow separation and for modifying the potential-flow solution due to the same are discussed, and numerical simulations are presented for comparison. [Preview Abstract] |
Tuesday, November 23, 2010 2:34PM - 2:47PM |
QX.00009: The Effect of Convex Sleeve on Cavitation Inception in the Rotary Valve of the Power Steering System Gwi Taek Kim, Sun Hong Park, Myung Hwan Cho, Jung Yul Yoo The rotary valve in power steering system helps the drivers turn the wheel with ease, when they set the vehicle in motion. It is well known that the hiss noise in the rotary valve occurs by the cavitating oil due to high pressure drop at the orifice. In this paper, the flows in two types ( Round and Straight types ) of rotary valves have been analyzed numerically by using three-dimensional cavitation model embedded in the commercial code, FLUENT 12.0. The shapes of the sleeve grooves are convex and rectangular respectively in the Round and Straight types. The numerical results have been compared with the hiss noise level measured in a semi-anechoic chamber. It is found that the shape of the sleeve grooves affects considerably the volume of the oil vapor generated from cavitation. These results can be utilized for the improved design of the hydraulic rotary valve with hiss noise reduction. [Preview Abstract] |
Tuesday, November 23, 2010 2:47PM - 3:00PM |
QX.00010: Characterization of Turbulence and Cavitation Induced Pipe Vibrations Due to Flow thru Baffle Plates Gavin Holt, Daniel Maynes, Jonathan Blotter We report experimental results characterizing pipe vibrations caused by turbulent flow and cavitation due to water flow through baffle plates mounted in a 10.2 cm diameter schedule 40 PVC pipe test section of a closed water flow loop. The baffle plates contained varying hole sizes that ranged from 0.159 cm to 2.54 cm, with the total through area, or openness, of each baffle plate ranging between 11{\%} and 60{\%}. Pipe wall acceleration data was collected for a range of Reynolds numbers from 5-85 x 10$^{4}$. Acceleration measurements were acquired at locations along the pipe from 3-110 diameters downstream of the baffle plate. The measurements show that vibration levels at a given streamwise position increase with larger holes size, a decrease in openness, and increased flow rate. The incipient point of cavitation was observed to occur at decreasing flow rate with increasing hole size and decreasing openness. Vibration levels decreased asymptotically with increased distance downstream of the baffle plate for all scenarios and the streamwise distance at which the vibration level was attenuated increased as the hole size increased, openness decreased, and flow rate increased. The downstream vibration level also increased with these parameters. [Preview Abstract] |
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