Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 146

Search results for: Vortex sheet

146 A Further Improvement on the Resurrected Core-Spreading Vortex Method

Authors: M-J. Huang, C-J. Huang, L-C. Chen

Abstract:

In a previously developed fast vortex method, the diffusion of the vortex sheet induced at the solid wall by the no-slip boundary conditions was modeled according to the approximation solution of Koumoutsakos and converted into discrete blobs in the vicinity of the wall. This scheme had been successfully applied to a simulation of the flow induced with an impulsively initiated circular cylinder. In this work, further modifications on this vortex method are attempted, including replacing the approximation solution by the boundary-element-method solution, incorporating a new algorithm for handling the over-weak vortex blobs, and diffusing the vortex sheet circulation in a new way suitable for high-curvature solid bodies. The accuracy is thus largely improved. The predictions of lift and drag coefficients for a uniform flow past a NASA airfoil agree well with the existing literature.

Keywords: Resurrected core-spreading vortex method, Boundaryelement method, Vortex sheet, Over-weak vortex blobs.

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145 Vortex Wake Formation and Its Effects on Thrust and Propulsive Efficiency of an Oscillating Airfoil

Authors: Ahmet Selim Durna, Bayram Celik, Aydin Misirlioglu

Abstract:

Flows over a harmonically oscillating NACA 0012 airfoil are simulated here using a two-dimensional, unsteady, incompressibleNavier-Stokes solver.Both pure-plunging and pitching-plunging combined oscillations are considered at a Reynolds number of 5000. Special attention is paid to the vortex shedding and interaction mechanism of the motions. For all the simulations presented here, the reduced frequency (k) is fixed at a value of 2.5 and plunging amplitude (h) is selected to be in the range of 0.2-0.5. The simulation results show that the interaction mechanism between the leading and trailing edge vortices has a decisive effect on the values of the resulting thrust and propulsive efficiency.

Keywords: pithing and plunging airfoil, leading edge vortex, trailing edge vortex, vortex interaction, wake structure.

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144 On Modified Numerical Schemes in Vortex Element Method for 2D Flow Simulation Around Airfoils

Authors: Ilia Marchevsky, Victoriya Moreva

Abstract:

The problem of incompressible steady flow simulation around an airfoil is discussed. For some simplest airfoils (circular, elliptical, Zhukovsky airfoils) the exact solution is known from complex analysis. It allows to compute the intensity of vortex layer which simulates the airfoil. Some modifications of the vortex element method are proposed and test computations are carried out. It-s shown that the these approaches are much more effective in comparison with the classical numerical scheme.

Keywords: Vortex element method, vortex layer, integral equation, ill-conditioned matrix.

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143 Influence of After Body Shape on the Performance of Blunt Shaped Bodies as Vortex Shedders

Authors: Lavish Ordia, A. Venugopal, Amit Agrawal, S. V. Prabhu

Abstract:

The present study explores flow visualization experiments with various blunt shaped bluff bodies placed inside a circular pipe. The bodies mainly comprise of modifications of trapezoidal cylinder, most widely used in practical applications, such as vortex flowmeters. The present configuration possesses the feature of both internal and external flows with low aspect ratio. The vortex dynamics of bluff bodies in such configuration is seldom reported in the literature. Dye injection technique is employed to visualize the complex vortex formation mechanism behind the bluff bodies. The influence of orientation, slit and after body shape is studied in an attempt to obtain better understanding of the vortex formation mechanism. Various wake parameters like Strouhal number, vortex formation length and wake width are documented for these shapes. Vortex formation both with and without shear layer interaction is observed for most of the shapes.

Keywords: Flow visualization, Reynolds number, Strouhal number, vortex, vortex formation length, wake width.

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142 Application of Vortex Induced Vibration Energy Generation Technologies to the Offshore Oil and Gas Platform: The Preliminary Study

Authors: M. A. Zahari, S. S. Dol

Abstract:

The global demand for continuous and eco-friendly renewable energy as alternative to fossils fuels is large and ever growing in nowadays. This paper will focus on capability of Vortex Induced Vibration (VIV) phenomenon in generating alternative energy for offshore platform application. In order to maximize the potential of energy generation, the effects of lock in phenomenon and different geometries of cylinder were studied in this project. VIV is the motion induced on bluff body which creates alternating lift forces perpendicular to fluid flow. Normally, VIV is unwanted in order to prevent mechanical failure of the vibrating structures. But in this project, instead of eliminating these vibrations, VIV will be exploited to transform these vibrations into a valuable resource of energy.

Keywords: Vortex Induced Vibration, Vortex Shedding, Renewable Energy

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141 Weakened Vortex Shedding from a Rotating Cylinder

Authors: Sharul S. Dol

Abstract:

An experimental study of the turbulent near wake of a rotating circular cylinder was made at a Reynolds number of 2000 for velocity ratios, λ between 0 and 2.7. Particle image velocimetry data are analyzed to study the effects of rotation on the flow structures behind the cylinder. The results indicate that the rotation of the cylinder causes significant changes in the vortex formation. Kármán vortex shedding pattern of alternating vortices gives rise to strong periodic fluctuations of a vortex street for λ < 2.0. Alternate vortex shedding is weak and close to being suppressed at λ = 2.0 resulting a distorted street with vortices of alternating sense subsequently being found on opposite sides. Only part of the circulation is shed due to the interference in the separation point, mixing in the base region, re-attachment, and vortex cut-off phenomenon. Alternating vortex shedding pattern diminishes and completely disappears when the velocity ratio is 2.7. The shed vortices are insignificant in size and forming a single line of vortex street. It is clear that flow asymmetries will deteriorate vortex shedding, and when the asymmetries are large enough, total inhibition of a periodic street occurs.

Keywords: Circulation, particle image velocimetry, rotating circular cylinder, smoke-wire flow visualization, Strouhal number, vortex shedding, vortex street.

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140 An Experimental Study of Tip Vortex Cavitation Inception in an Axial Flow Pump

Authors: Mohammad Taghi Shervani Tabar, Zahra Poursharifi

Abstract:

The interaction of the blade tip with the casing boundary layer and the leakage flow may lead to a kind of cavitation namely tip vortex cavitation. In this study, the onset of tip vortex cavitation was experimentally investigated in an axial flow pump. For a constant speed and a fixed angle of attack and by changing the flow rate, the pump head, input power, output power and efficiency were calculated and the pump characteristic curves were obtained. The cavitation phenomenon was observed with a camera and a stroboscope. Finally, the critical flow region, which tip vortex cavitation might have occurred, was identified. The results show that just by adjusting the flow rate, out of the specified region, the possibility of occurring tip vortex cavitation, decreases to a great extent.

Keywords: Axial flow pump, Gap cavitation, Leakage vortex, Tip vortex cavitation.

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139 Energy Separation Mechanism in Uni-Flow Vortex Tube Using Compressible Vortex Flow

Authors: Hiroshi Katanoda, Mohd Hazwan bin Yusof

Abstract:

A theoretical investigation from the view point of gas-dynamics and thermodynamics was carried out, in order to clarify the energy separation mechanism in a viscous compressible vortex, as a primary flow element in a uni-flow vortex tube. The mathematical solutions of tangential velocity, density and temperature in a viscous compressible vortical flow were used in this study.It is clear that a total temperature in the vortex core falls well below that distant from the vortex core in the radial direction, causing aregion with higher total temperature,compared to the distant region,peripheral to the vortex core.

Keywords: Energy separation mechanism, theoretical analysis, vortex tube, vortical flow.

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138 Location of Vortex Formation Threshold at Suction Inlets near Ground Planes – Ascending and Descending Conditions

Authors: Wei Hua Ho

Abstract:

Vortices can develop in intakes of turbojet and turbo fan aero engines during high power operation in the vicinity of solid surfaces. These vortices can cause catastrophic damage to the engine. The factors determining the formation of the vortex include both geometric dimensions as well as flow parameters. It was shown that the threshold at which the vortex forms or disappears is also dependent on the initial flow condition (i.e. whether a vortex forms after stabilised non vortex flow or vice-versa). A computational fluid dynamics study was conducted to determine the difference in thresholds between the two conditions. This is the first reported numerical investigation of the “memory effect". The numerical results reproduce the phenomenon reported in previous experimental studies and additional factors, which had not been previously studied, were investigated. They are the rate at which ambient velocity changes and the initial value of ambient velocity. The former was found to cause a shift in the threshold but not the later. It was also found that the varying condition thresholds are not symmetrical about the neutral threshold. The vortex to no vortex threshold lie slightly further away from the neutral threshold compared to the no vortex to vortex threshold. The results suggests that experimental investigation of vortex formation threshold performed either in vortex to no vortex conditions, or vice versa, solely may introduce mis-predictions greater than 10%.

Keywords: Jet Engine Test Cell, Unsteady flow, Inlet Vortex

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137 Vortex-Shedding Suppression in Mixed Convective Flow past a Heated Square Cylinder

Authors: A. Rashid, N. Hasan

Abstract:

The present study investigates numerically the phenomenon of vortex-shedding and its suppression in twodimensional mixed convective flow past a square cylinder under the joint influence of buoyancy and free-stream orientation with respect to gravity. The numerical experiments have been conducted at a fixed Reynolds number (Re) of 100 and Prandtl number (Pr) of 0.71, while Richardson number (Ri) is varied from 0 to 1.6 and freestream orientation, α, is kept in the range 0o≤ α ≤ 90o, with 0o corresponding to an upward flow and 90o representing a cross-flow scenario, respectively. The continuity, momentum and energy equations, subject to Boussinesq approximation, are discretized using a finite difference method and are solved by a semi-explicit pressure correction scheme. The critical Richardson number, leading to the suppression of the vortex-shedding (Ric), is estimated by using Stuart-Landau theory at various free-stream orientations and the neutral curve is obtained in the Ri-α plane. The neutral curve exhibits an interesting non-monotonic behavior with Ric first increasing with increasing values of α upto 45o and then decreasing till 70o. Beyond 70o, the neutral curve again exhibits a sharp increasing asymptotic trend with Ric approaching very large values as α approaches 90o. The suppression of vortex shedding is not observed at α = 90o (cross-flow). In the unsteady flow regime, the Strouhal number (St) increases with the increase in Richardson number.

Keywords: bluff body, buoyancy, free-stream orientation, vortex-shedding.

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136 Numerical Investigation of the Thermal Separation in a Vortex Tube

Authors: N.Pourmahmoud, S.Akhesmeh

Abstract:

This work has been carried out in order to provide an understanding of the physical behaviors of the flow variation of pressure and temperature in a vortex tube. A computational fluid dynamics model is used to predict the flow fields and the associated temperature separation within a Ranque–Hilsch vortex tube. The CFD model is a steady axisymmetric model (with swirl) that utilizes the standard k-ε turbulence model. The second–order numerical schemes, was used to carry out all the computations. Vortex tube with a circumferential inlet stream and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. Performance curves (temperature separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate. Simulations have been carried out for varying amounts of cold outlet mass flow rates. The model results have a good agreement with experimental data.

Keywords: Ranque–Hilsch vortex tube, Temperature separation, k–ε model, cold mass fraction.

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135 Study of Unsteady Swirling Flow in a Hydrodynamic Vortex Chamber

Authors: Sergey I. Shtork, Aleksey P. Vinokurov, Sergey V. Alekseenko

Abstract:

The paper reports on the results of experimental and numerical study of nonstationary swirling flow in an isothermal model of vortex burner. It has been identified that main source of the instability is related to a precessing vortex core (PVC) phenomenon. The PVC induced flow pulsation characteristics such as precession frequency and its variation as a function of flowrate and swirl number have been explored making use of acoustic probes. Additionally pressure transducers were used to measure the pressure drops on the working chamber and across the vortex flow. The experiments have been included also the mean velocity measurements making use of a laser-Doppler anemometry. The features of instantaneous flowfield generated by the PVC were analyzed employing a commercial CFD code (Star-CCM+) based on Detached Eddy Simulation (DES) approach. Validity of the numerical code has been checked by comparison calculated flowfield data with the obtained experimental results. It has been confirmed particularly that the CFD code applied correctly reproduces the flow features.

Keywords: Acoustic probes, detached eddy simulation (DES), laser-Doppler anemometry (LDA), precessing vortex core (PVC).

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134 Vortex Shedding on Combined Bodies at Incidence to a Uniform Air Stream

Authors: T. Yavuz, Y. E. Akansu, M. Sarıoglu, M. Ozmert

Abstract:

Vortex-shedding phenomenon of the flow around combined two bodies having various geometries and sizes has been investigated experimentally in the Reynolds number range between 4.1x103 and 1.75x104. To see the effect of the rotation of the bodies on the vortex shedding, the combined bodies were rotated from 0° to 180°. The combined models have a cross section composing of a main circular cylinder and an attached circular or square cylinder. Results have shown that Strouhal numbers for two cases were changed considerably with the angle of incidence, while it was found to be largely independent of Reynolds number at 150. Characteristics of the vortex formation region and location of flow attachments, reattachments, and separations were observed by means of the flow visualizations. Depending on the inclination angle the effects of flow attachment, separation and reattachment on vortex-shedding phenomenon have been discussed.

Keywords: Bluff body, vortex shedding, flow separation, flow reattachment

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133 Interaction between Unsteady Supersonic Jet and Vortex Rings

Authors: Kazumasa Kitazono, Hiroshi Fukuoka, Nao Kuniyoshi, Minoru Yaga, Eri Ueno, Naoaki Fukuda, Toshio Takiya

Abstract:

The unsteady supersonic jet formed by a shock tube with a small high-pressure chamber was used as a simple alternative model for pulsed laser ablation. Understanding the vortex ring formed by the shock wave is crucial in clarifying the behavior of unsteady supersonic jet discharged from an elliptical cell. Therefore, this study investigated the behavior of vortex rings and a jet. The experiment and numerical calculation were conducted using the schlieren method and by solving the axisymmetric two-dimensional compressible Navier–Stokes equations, respectively. In both, the calculation and the experiment, laser ablation is conducted for a certain duration, followed by discharge through the exit. Moreover, a parametric study was performed to demonstrate the effect of pressure ratio on the interaction among vortex rings and the supersonic jet. The interaction between the supersonic jet and the vortex rings increased the velocity of the supersonic jet up to the magnitude of the velocity at the center of the vortex rings. The interaction between the vortex rings increased the velocity at the center of the vortex ring.

Keywords: Computational fluid dynamics, shock wave, unsteady jet, vortex ring.

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132 Analysis of Vortex-Induced Vibration Characteristics for a Three-Dimensional Flexible Tube

Authors: Zhipeng Feng, Huanhuan Qi, Pingchuan Shen, Fenggang Zang, Yixiong Zhang

Abstract:

Numerical simulations of vortex-induced vibration of a three-dimensional flexible tube under uniform turbulent flow are calculated when Reynolds number is 1.35×104. In order to achieve the vortex-induced vibration, the three-dimensional unsteady, viscous, incompressible Navier-Stokes equation and LES turbulence model are solved with the finite volume approach, the tube is discretized according to the finite element theory, and its dynamic equilibrium equations are solved by the Newmark method. The fluid-tube interaction is realized by utilizing the diffusion-based smooth dynamic mesh method. Considering the vortex-induced vibration system, the variety trends of lift coefficient, drag coefficient, displacement, vertex shedding frequency, phase difference angle of tube are analyzed under different frequency ratios. The nonlinear phenomena of locked-in, phase-switch are captured successfully. Meanwhile, the limit cycle and bifurcation of lift coefficient and displacement are analyzed by using trajectory, phase portrait, and Poincaré sections. The results reveal that: when drag coefficient reaches its minimum value, the transverse amplitude reaches its maximum, and the “lock-in” begins simultaneously. In the range of lock-in, amplitude decreases gradually with increasing of frequency ratio. When lift coefficient reaches its minimum value, the phase difference undergoes a suddenly change from the “out-of-phase” to the “in-phase” mode.

Keywords: Vortex induced vibration, limit cycle, CFD, FEM.

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131 Interface Analysis of Annealed Al/Cu Cladded Sheet

Authors: Joon Ho Kim, Tae Kwon Ha

Abstract:

Effect of aging treatment on microstructural aspects of interfacial layers of the Cu/Al clad sheet produced by differential speed rolling (DSR) process were studied by electron back scattered diffraction (EBSD). Clad sheet of Al/Cu has been fabricated by using DSR, which caused severe shear deformation between Al and Cu plate to easily bond to each other. Rolling was carried out at 100oC with speed ratio of 2, in which the total thickness reduction was 45%. Interface layers of clad sheet were analyzed by EBSD after subsequent annealing at 400oC for 30 to 120min. With increasing annealing time, thickness of interface layer and fraction of high angle grain boundary were increased and average grain size was decreased.

Keywords: Aluminum/Copper clad sheet, differential speed rolling, interface layer, microstructure, annealing, electron back scattered diffraction.

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130 Speedup of Data Vortex Network Architecture

Authors: Qimin Yang

Abstract:

In this paper, 3X3 routing nodes are proposed to provide speedup and parallel processing capability in Data Vortex network architectures. The new design not only significantly improves network throughput and latency, but also eliminates the need for distributive traffic control mechanism originally embedded among nodes and the need for nodal buffering. The cost effectiveness is studied by a comparison study with the previously proposed 2- input buffered networks, and considerable performance enhancement can be achieved with similar or lower cost of hardware. Unlike previous implementation, the network leaves small probability of contention, therefore, the packet drop rate must be kept low for such implementation to be feasible and attractive, and it can be achieved with proper choice of operation conditions.

Keywords: Data Vortex, Packet Switch, Interconnection network, deflection, Network-on-chip

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129 Fabrication of Al/Cu Clad Sheet by Shear Extrusion

Authors: Joon Ho Kim, Duck Su Kim, Tae Kwon Ha

Abstract:

Aluminum/Copper clad sheet has been fabricated using asymmetric extrusion method, which caused severe shear deformation between Al and Cu plate to easily bond to each other. Interfacial microstructure and mechanical properties of Al/Cu clad were studied by scanning electron microscope equipped with energy dispersive X-ray detector, micro-hardness, and tension tests. The asymmetric extrusion bonding was very effective to provide a good interface for atoms diffusion during subsequent annealing. The strength of bonding was higher with the increasing extrusion ratio.

Keywords: Aluminum/Copper clad sheet, Asymmetric extrusion, Interfacial microstructure, Annealing, Tensile test.

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128 Properties of MWCNTs/PAN Nanofiber Sheet Prepared from Chemically Modified MWCNTs

Authors: M. Seneewong-Na-Ayuttaya, T. Pongprayoon

Abstract:

The nanofiber sheet of Multiwall Cabon Nanotube (MWCNTs)/Polyacylonitile (PAN) composites was fabricated from electrospun nanofiber. Firstly the surface of MWCNTs was chemically modified, comparing two different techniques consisting of admicellar polymerization and functionalization to improve the dispersion and prevent the aggregation in the PAN matrix. The modified MWCNTs were characterized by the dispersion in dimethylformamide (DMF) solvent, Laser particle size, and FTRaman. Lastly, DSC, SEM and mechanical properties of the nanofiber sheet were examined. The results show that the mechanical properties of the nanofiber sheet prepared from admicellar polymerization-modified MWCNTs were higher than those of the others.

Keywords: Multiwall carbon nanotube, admicellar polymerization, functionalization, nanofiber sheet.

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127 Application of Vortex Induced Vibration Energy Generation Technologies to the Offshore Oil and Gas Platform: The Feasibility Study

Authors: T. Yui Khing, M. A. Zahari, S. S. Dol

Abstract:

Ocean current is always available around the surrounding of SHELL Sabah Water Platform and data are collected every 10 minutes, 24 hours a day, for a period of 365 days. Due to low current speed, conventional hydrokinetic power generation is not feasible, thus leading to the study of low current enabled vortex induced vibration power generation application. In this case, the design of a vortex induced vibration application is studied to obtain an optimum design for the VIV oscillator. Power output is then determined to study the feasibility of the VIV application in low current condition.

Keywords: Renewable energy, Vortex induced vibration, Turbulence, Lock-in.

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126 Flow and Heat Transfer of a Nanofluid over a Shrinking Sheet

Authors: N. Bachok, N. L. Aleng, N. M. Arifin, A. Ishak, N. Senu

Abstract:

The problem of laminar fluid flow which results from the shrinking of a permeable surface in a nanofluid has been investigated numerically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented which depends on the mass suction parameter S, Prandtl number Pr, Lewis number Le, Brownian motion number Nb and thermophoresis number Nt. It was found that the reduced Nusselt number is decreasing function of each dimensionless number.

Keywords: Boundary layer, Nanofluid, Shrinking sheet, Brownian motion, Thermophoresis, Similarity solution.

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125 Bearing Capacity of Sheet Hanger Connection to the Trapezoidal Metal Sheet

Authors: Kateřina Jurdová

Abstract:

Hanging to the trapezoidal sheet by decking hanger is a very widespread solution used in civil engineering to lead the distribution of energy, sanitary, air distribution system etc. under the roof or floor structure. The trapezoidal decking hanger is usually a part of the whole installation system for specific distribution medium. The leading companies offer installation systems for each specific distribution e.g. pipe rings, sprinkler systems, installation channels etc. Every specific part is connected to the base connector which is decking hanger. The own connection has three main components: decking hanger, threaded bar with nuts and web of trapezoidal sheet. The aim of this contribution is determinate the failure mechanism of each component in connection. Load bearing capacity of most components in connection could be calculated by formulas in European codes. This contribution is focused on problematic of bearing resistance of threaded bar in web of trapezoidal sheet. This issue is studied by experimental research and numerical modelling. This contribution presented the initial results of experiment which is compared with numerical model of specimen.

Keywords: Decking hanger, concentrated load, connection, load bearing capacity, trapezoidal metal sheet.

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124 Application of Vortex Tubes for Extracting Sediments Using SHARC Software - A Case Study of the Western Canal in the Dez Diversion Weir

Authors: A. H. Sajedi Pour, N. Hedayat, Z. Yazdi

Abstract:

Sediment loads transfer in hydraulic installations and their consequences for the O&M of modern canal systems is emerging as one of the most important considerations in hydraulic engineering projects apriticularly those which are inteded to feed the irrigation and draiange schemes of large command areas such as the Dez and Mogahn in Iran.. The aim of this paper is to investigate the applicability of the vortex tube as a viable means of extracting sediment loads entering the canal systems in general and the water inatke structures in particulars. The Western conveyance canal of the Dez Diversion weir which feeds the Karkheh Flood Plain in Sothwestern Dezful has been used as the case study using the data from the Dastmashan Hydrometric Station. The SHARC software has been used as an analytical framework to interprete the data. Results show that given the grain size D50 and the canal turbulence the adaption length from the beginning of the canal and after the diversion dam is estimated at 477 m, a point which is suitable for laying the vortex tube.

Keywords: Vortex tube, sediments, western canal, SHARCmodel

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123 Vortex-Induced Vibration Characteristics of an Elastic Circular Cylinder

Authors: T. Li, J.Y. Zhang, W.H. Zhang, M.H. Zhu

Abstract:

A numerical simulation of vortex-induced vibration of a 2-dimensional elastic circular cylinder with two degree of freedom under the uniform flow is calculated when Reynolds is 200. 2-dimensional incompressible Navier-Stokes equations are solved with the space-time finite element method, the equation of the cylinder motion is solved with the new explicit integral method and the mesh renew is achieved by the spring moving mesh technology. Considering vortex-induced vibration with the low reduced damping parameter, the variety trends of the lift coefficient, the drag coefficient, the displacement of cylinder are analyzed under different oscillating frequencies of cylinder. The phenomena of locked-in, beat and phases-witch were captured successfully. The evolution of vortex shedding from the cylinder with time is discussed. There are very similar trends in characteristics between the results of the one degree of freedom cylinder model and that of the two degree of freedom cylinder model. The streamwise vibrations have a certain effect on the lateral vibrations and their characteristics.

Keywords: Fluid-structure interaction, Navier-Stokes equation, Space-time finite element method, vortex-induced vibration.

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122 Experimental Study of Performance of a Counter Flow Ranque-Hilsch Vortex Tube with Inner Threaded Body

Authors: Gürol Önal, Kevser Dincer

Abstract:

In this experimental study, performance of a counter flow Ranque-Hilsch vortex tube (RHVT) with threads cut on its inner surface was investigated experimentally (pitch is 1 and 2 mm). The inner diameter of the vortex tube used was D=9 mm and the ratio of the tube’s length to diameter was L/D=12. The experimental system was a thermodynamic open system. Flow was controlled by a valve on the hot outlet side, where the valve was changed from a nearly closed position to its nearly open position. Fraction of cold flow (ξ) = 0.1-0.9, was determined under 300 and 350 kPa pressurized air. All experimental data were compared with each other, the maximum heating performance of the RHVT system was found to be 38.2 oC and the maximum cooling performance of the RHVT in this study was found to be -30.9 oC at pitch 1 mm.

Keywords: Ranque-Hilsch vortex tube, heating, cooling, temperature separation.

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121 The Role of Periodic Vortex Shedding in Heat Transfer Enhancement for Transient Pulsatile Flow Inside Wavy Channels

Authors: Esam M. Alawadhi, Raed I. Bourisli

Abstract:

Periodic vortex shedding in pulsating flow inside wavy channel and the effect it has on heat transfer are studied using the finite volume method. A sinusoidally-varying component is superimposed on a uniform flow inside a sinusoidal wavy channel and the effects on the Nusselt number is analyzed. It was found that a unique optimum value of the pulsation frequency, represented by the Strouhal number, exists for Reynolds numbers ranging from 125 to 1000. Results suggest that the gain in heat transfer is related to the process of vortex formation, movement about the troughs of the wavy channel, and subsequent ejection/destruction through the converging section. Heat transfer is the highest when the frequencies of the pulsation and vortex formation approach being in-phase. Analysis of Strouhal number effect on Nu over a period of pulsation substantiates the proposed physical mechanism for enhancement. The effect of changing the amplitude of pulsation is also presented over a period of pulsation, showing a monotonic increase in heat transfer with increasing amplitude. The 60% increase in Nusselt number suggests that sinusoidal fluid pulsation can an effective method for enhancing heat transfer in laminar, wavy-channel flows.

Keywords: Vortex shedding, pulsating flow, wavy channel, CFD.

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120 Wave Vortex Parameters as an Indicator of Breaking Intensity

Authors: B. Robertson, K. Hall

Abstract:

The study of the geometric shape of the plunging wave enclosed vortices as a possible indicator for the breaking intensity of ocean waves has been ongoing for almost 50 years with limited success. This paper investigates the validity of using the vortex ratio and vortex angle as methods of predicting breaking intensity. Previously published works on vortex parameters, based on regular wave flume results or solitary wave theory, present contradictory results and conclusions. Through the first complete analysis of field collected irregular wave breaking vortex parameters it is illustrated that the vortex ratio and vortex angle cannot be accurately predicted using standard breaking wave characteristics and hence are not suggested as a possible indicator for breaking intensity.

Keywords: Breaking Wave Measurement, Wave Vortex Parameters, Analytical Techniques, Ocean Remote Sensing.

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119 Classification of Buckling Behavior on Uniaxial Compression using A5052-O Sheets

Authors: S. Onoda, S. Yoshihara, B. J. MacDonald, Y. Okude

Abstract:

Aluminum alloy sheets have several advantages such as the lightweight, high-specific strength and recycling efficiency. Therefore, aluminum alloy sheets in sheet forming have been used in various areas as automotive components and so forth. During the process of sheet forming, wrinkling which is caused by compression stress might occur and the formability of sheets was affected by occurrence of wrinkling. A few studies of uniaxial compressive test by using square tubes, pipes and sheets were carried out to clarify the each wrinkling behavior. However, on uniaxial compressive test, deformation behavior of the sheets hasn-t be cleared. Then, it is necessary to clarify the relationship between the buckling behavior and the forming conditions. In this study, the effect of dimension of the sheet in the buckling behavior on compression test of aluminum alloy sheet was cleared by experiment and FEA. As the results, the buckling deformation was classified by three modes in terms of the distribution of equivalent plastic strain.

Keywords: Sheet forming, Compression test, Aluminum alloy sheet, Buckling behavior

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118 A Vortex Plate Theory of Hovering Animal Flight

Authors: Khaled. M. Faqih

Abstract:

A model of vortex wake is suggested to determine the induced power during animal hovering flight. The wake is modeled by a series of equi-spaced rigid rectangular vortex plates, positioned horizontally and moving vertically downwards with identical speeds; each plate is generated during powering of the functionally wing stroke. The vortex representation of the wake considered in the current theory allows a considerable loss of momentum to occur. The current approach accords well with the nature of the wingbeat since it considers the unsteadiness in the wake as an important fluid dynamical characteristic. Induced power in hovering is calculated as the aerodynamic power required to generate the vortex wake system. Specific mean induced power to mean wing tip velocity ratio is determined by solely the normal spacing parameter (f) for a given wing stroke amplitude. The current theory gives much higher specific induced power estimate than anticipated by classical methods.

Keywords: vortex theory, hovering flight, induced power, Prandlt's tip theory.

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117 Numerical Study of Base Drag Reduction Using Locked Vortex Flow Management Technique for Lower Subsonic Regime

Authors: Kailas S. Jagtap, Karthik Sundarraj, Nirmal Kumar, S. Rajnarasimha, Prakash S. Kulkarni

Abstract:

The issue of turbulence base streams and the drag related to it have been of important attention for rockets, missiles, and aircraft. Different techniques are used for base drag reduction. This paper presents the numerical study of numerous drag reduction technique. The base drag or afterbody drag of bluff bodies can be reduced easily using locked vortex drag reduction technique. For bluff bodies having a cylindrical shape, the base drag is much larger compared to streamlined bodies. For such bodies using splitter plates, the vortex can be trapped between the base and the plate, which results in smooth flow. Splitter plate with round and curved corner shapes has influence in drag reduction. In this paper, the comparison is done between single splitter plate as different positions and with the bluff body. Base drag for the speed of 30m/s can be reduced about 20% to 30% by using single splitter plate as compared to the bluff body.

Keywords: Base drag, bluff body, splitter plate, vortex flow, ANSYS, Fluent.

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