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research-article  
Anup Kumer DATTA, Yasutaka HAYAMIZU, Toshinori KOUCHI, Yasunori NAGATA, Kyoji YAMAMOTO and Shinichiro YANASE
J. Fluids Eng   doi: 10.1115/1.4036477
Turbulent flows through helical pipes with circular cross section are numerically investigated comparing with the experimental results obtained by our team. Numerical calculations are carried out for two helical circular pipes having different pitches and the same non-dimensional curvature δ (= 0.1) over a wide range of the Reynolds number, Re, from 3000 to 21000 for torsion parameter ß (= torsion /2δ = 0.02 and 0.45). We numerically obtained the secondary flow, the axial flow and the intensity of the turbulent kinetic energy by use of three turbulence models incorporated in OpenFOAM. We found that RNG k-ε turbulence model can predict excellently the fully developed turbulent flow with comparison to the experimental data. It is found that the momentum transfer due to turbulence dominates the secondary flow pattern of the turbulent helical pipe flow. It is interesting that torsion effect is more remarkable for turbulent flows than laminar flows.
TOPICS: Turbulence, Pipe flow, Torsion, Flow (Dynamics), Pipes, Axial flow, Fully developed turbulent flow, Teams, Kinetic energy, Laminar flow, Reynolds number, Momentum
research-article  
Diego N. Venturi, Waldir P. Martignoni, Dirceu Noriler and Henry F. Meier
J. Fluids Eng   doi: 10.1115/1.4036444
Two-phase flows across tube bundles are very commonly found in industrial heat exchange equipment such as shell and tube heat exchangers. However, recent studies published in the literature are generally performed on devices where the flow crosses the tube bundle in only a vertical or horizontal direction, lacking geometrical fidelity with industrial models, and the majority of them use air and water as the working fluids. Also, currently, experimental approaches and simulations are based on very simplified models. This paper reports the simulation of a laboratory full-scale tube bundle with a combination of vertical and horizontal flows and, with two different baffle configurations. Also, it presents a similarity analysis to evaluate the influence of changing the fluids to hydrogen and diesel in the operational conditions of the hydrotreating. The volume of fluid (VOF) approach is used as the interface phenomena is very important. The air/water simulations show good agreement with classical correlations and are able to show the stratified behavior of the flow in horizontal regions and the intermittent flow in the vertical regions. Also the two baffle configurations are compared in terms of volume fraction and streamlines. When dealing with hydrogen/diesel flow using correlations and maps made for air/water, superficial velocity is recommended as similarity variable when a better prediction of the pressure drop is needed, and the modified superficial velocity is recommended for prediction of the volume-average void fraction and the outlet superficial void fraction.
TOPICS: Flow (Dynamics), Diesel, Hydrogen, Water, Fluids, Simulation, Porosity, Pressure drop, Shells, Experimental methods, Heat exchangers, Two-phase flow, Interface phenomena, Heat
research-article  
Xin Wen and Hui Tang
J. Fluids Eng   doi: 10.1115/1.4036410
This paper presents a parametric study on the interaction of twin circular synthetic jets (SJs) that are in line with a crossflow over a flat plate. The resulting vortex structures under differ- ent actuation and flow conditions are investigated using stereoscopic color dye visualization in a water tunnel. The influence of four independent non-dimensional parameters, i.e., the Reynolds number ReL, Strouhal number St, velocity ratio V R, and phase difference ?f, on the behavior of the twin SJs is studied. It is found that the increase of Reynolds number causes the SJ-induced vortex structures more turbulent, making the twin SJ interaction less organized; The increase of velocity ratio pushes the occurrence of interaction further away from the wall, and makes the resulting vortex structures more sustainable; The Strouhal number has no obvious influence on the interaction; And three types of vortex structures are observed under different phase differences: one combined vortex, two completely separated vortices, and partially interacting vortex structures. Based on this parametric study, a simple model is proposed to predict the resulting vortex pattern for the twin SJ interaction.
TOPICS: Jets, Visualization, Vortices, Reynolds number, Flat plates, Water tunnels, Sustainability, Flow (Dynamics), Turbulence
research-article  
Jerome Griffond, Jean-Francois Haas, Denis Souffland, Ghazi Bouzgarrou, Yannick Bury and Stephane Jamme
J. Fluids Eng   doi: 10.1115/1.4036369
Shock induced mixing experiments have been conducted in a vertical shock tube of 130 mm square cross-section located at ISAE. A shock wave travelling at Mach 1.2 in air hits a geometrically disturbed interface separating air and SF6, a gas 5 times heavier than air, filling a chamber of length L up to the end of the shock tube. Both gases are initially separated by a 0.5 micron thick nitrocellulose membrane maintained parallel to the shock front by two wire grids: an upper one with mesh spacing equal to either m_s=1.8 mm or 12.1 mm, and a lower one with a mesh spacing equal to m_l=1 mm. Weak dependence of the mixing zone growth after reshock (interaction of the mixing zone with the shock wave reflected from the top end of the test chamber) with respect to L and m_s is observed despite a clear imprint of the mesh spacing m_s in the schlieren images. Numerical simulations representative of these configurations are conducted:the simulations successfully replicate the experimentally observed weak dependence on L, but are unable to show the experimentally observed independence with respect to m_s while matching the morphological features of the schlieren pictures.
TOPICS: Turbulence, Shock tubes, Shock waves, Wire, Simulation, Shock (Mechanics), Engineering simulation, Membranes, Gases, Computer simulation
research-article  
Lakhdar Remaki, Ali Ramezani, Jesus Maria Blanco and Imanol Garcia
J. Fluids Eng   doi: 10.1115/1.4036300
This paper deals with rotating effects simulation of steady flows in turbomachinery. To take into account the rotating nature of the flow,the frozen rotor approach is one of the most popular used approach. This techniques, known in a more general contexts as a multiple rotating frame (MRF), consists on building axisymmetric interfaces around the rotating parts and solve for the flow in different frames (static and rotating). This paper aimed to revisit this technique and propose a new algorithm (VMRF) where the geometrical interfaces (part of the CAD) that separate the rotating parts are replaced by a virtual ones created at the solver level by a simple user input of few points locations and/or parameters of basic shapes, rendering the method easy to implement especially for edge-based numerical schemes, very simple to use and avoiding any re-meshing (required by the MRF approach) when one needs to change interface position, shape or simply remove or add new one, which frequently happened in practice.Consequently, the new algorithm reduces sensibly the overall computations cost of a simulation.This work is an extension of a first version published in an ASME conference, and the main new contributions are the detailed description of the new algorithm in the context of cell-vertex finite volume method, and the validation of the method for the three dimensional case which is of a big importance to the method to be attractive for real and industrial applications.
TOPICS: Algorithms, Computational fluid dynamics, Flow (Dynamics), Simulation, Shapes, Turbomachinery, Computer-aided design, Rotors, Computation, Finite volume methods, Rendering
research-article  
Robert R. Long, Edward B. White, Nathan R. Tichenor and Kevin Kremeyer
J. Fluids Eng   doi: 10.1115/1.4036270
Experiments in ground-test facilities are required to develop and mature aero-optic platforms. However, structural vibrations of the facility can introduce significant error in optical experiments, making it difficult to separate wind tunnel dynamics from the aero-optic measurements of interest. As a means of performing this separation, a Kalman filtering scheme, tuned using the Autocovariance Least-Squares method, is implemented to measure the dynamic motion of a generalized aero-optic model geometry. An example is presented for the case of a laser diode mounted on a flexible post undergoing vibration. Using a single three-axis accelerometer, combined with a priori knowledge of the system’s structural dynamics, pitch angle fluctuations on the order of 0.01 degree were successfully estimated within 0.002 degree uncertainty.
TOPICS: Vibration measurement, Wind tunnels, Vibration, Errors, Geometry, Uncertainty, Dynamics (Mechanics), Separation (Technology), Lasers, Filtration, Accelerometers, Fluctuations (Physics), Structural dynamics
research-article  
Hassan M. Soliman
J. Fluids Eng   doi: 10.1115/1.4036266
The Jeffery-Hamel problem for laminar, radial flow between two nonparallel plates has been extended to the case of two immiscible fluids in slender channels. The governing continuity and momentum equations were solved numerically using the 4th order Runge-Kutta method. Solutions were obtained for air-water at standard conditions over the void-fraction range of 0.4 to 0.8 (due to its practical significance) and the computations were limited to conditions where unique solutions were found to exist. The void fraction, pressure gradient, wall friction coefficient, and interfacial friction coefficient are dependent on the Reynolds numbers of both fluids and the complex nature of this dependence is presented and discussed. An attempt to use a one-dimensional two-fluid with simplified assumptions succeeded in producing a qualitatively similar form of the void-fraction dependence on the two Reynolds numbers; however, quantitatively there are significant deviations between these results and those of the complete model.
TOPICS: Fluids, Radial flow, Wedges, Porosity, Friction, Reynolds number, Plates (structures), Computation, Momentum, Pressure gradient, Runge-Kutta methods, Water
research-article  
David Stefan, Pavel Rudolf, Sebastian Muntean and Romeo Susan-Resiga
J. Fluids Eng   doi: 10.1115/1.4036244
The swirling flow exiting the runner of a hydraulic turbine is further decelerated in the discharge cone of the draft tube to convert the excess of dynamic pressure into static pressure. When the turbine is operated far from the best efficiency regime, particularly at part load, the decelerated swirling flow develops a self-induced instability with a precessing helical vortex, with associated severe pressure fluctuations. This phenomenon is investigated numerically in this paper, for a swirl apparatus configuration. The unsteady three-dimensional flow field is analyzed using a proper orthogonal decomposition (POD), and within this framework we examine the effectiveness of an axial jet injection for mitigating the flow instability. It is shown that a limited number of modes can be used to reconstruct the flow field. Moreover, POD enables to reveal influence of the jet injection on the individual modes of the flow and illustrates continuous suppression of the modes from higher order modes to lower order modes as the jet discharge increases. Application of POD offers new view for the future control effort aimed on vortex rope mitigation, because spatio-temporal description of the flow is provided. Thereby POD enables better focus of the jets or other flow control devices.
TOPICS: Underground injection, Principal component analysis, Swirling flow, Flow (Dynamics), Pressure, Vortices, Flow control, Hydraulic turbines, Stress, Fluctuations (Physics), Jets, Flow instability, Turbines, Ropes
research-article  
Amir H. Azimi, Jianan Cai, David Z. Zhu and Nallamuthu Rajaratnam
J. Fluids Eng   doi: 10.1115/1.4036267
Withdrawal of water-capped viscoplastic fluid was investigated using laboratory experimentation and numerical modeling. The viscoplastic fluid was modeled using a Laponite suspension, which was withdrawn by a vertical pipe intake. Variations of the Laponite-water interface and intake configurations were investigated in this study. The critical submergence, the depth of the intake in the Laponite layer when the upper water begins to withdraw, was studied under different experimental conditions, and the critical depths were measured at different flow rates. An empirical relationship was found between the withdrawal flow rate and the critical submergence. The averaged Laponite velocity was measured at different withdrawal stages to identify the critical stage. A series of numerical simulations were conducted to study the effect of intake structures so that a maximum amount of the Laponite suspension can be withdrawn before the water layer being withdrawn. It was found that a combination of a collar and a cone with an edge length to the intake diameter of 1.5 can increase the pumping duration by 16.7%. The installation of a collar or collar-cone setup can also decrease the disturbance in Laponite layer.
TOPICS: Fluids, Water, Flow (Dynamics), Computer simulation, Pipes
research-article  
Matthew L. Talley, Matthew D. Zimmer and Igor A Bolotnov
J. Fluids Eng   doi: 10.1115/1.4036246
An algorithm to prevent or delay bubble coalescence for the Level Set (LS) method is presented. This novel algorithm uses the LS method field to detect when bubbles are in close proximity, indicating a potential coalescence event, and applies a repellent force to simulate the unresolved liquid drainage force. The model is introduced by locally modifying the surface tension force near the liquid film drainage area. The algorithm can also simulate the liquid drainage time of the thin film by controlling the length of time the increased surface tension has been applied. Thus a new method of modeling bubble coalescence has been developed. Several test cases were designed to demonstrate the capabilities of the algorithm. The simulations, including a mesh study, confirmed the abilities to identify and prevent coalescence as well as implement the time tracking portion, with an additional 10-25% computational cost. Ongoing tests aim to verify the algorithm’s functionality for simulations with different flow conditions, a ranging number of bubbles, and both structured and unstructured computational mesh types. Specifically, a bubble rising towards a free surface provides a test of performance and demonstrates the ability to consistently prevent coalescence. In addition, a two bubble case and a seven bubble case provide a more complex demonstration of how the algorithm performs for larger simulations. These cases are compared to much more expensive simulations capable of resolving the liquid film drainage (through very high local mesh resolution), to investigate how the algorithm replicates the liquid film drainage process.
TOPICS: Algorithms, Bubbles, Drainage, Simulation, Engineering simulation, Liquid films, Surface tension, Thin films, Flow (Dynamics), Resolution (Optics), Modeling, Delays
research-article  
Sergey G. Skripkin, Mikhail A. Tsoy, Pavel A. Kuibin and Sergey I. Shtork
J. Fluids Eng   doi: 10.1115/1.4036264
Operating hydraulic turbines under part- or over-load conditions leads to development of the precessing vortex rope downstream of the turbine runner. In a regime close to the best efficiency point, the vortex rope is very unstable because of the low residual swirl of the flow. However, strong pressure pulsations have been detected in such a regime. These oscillations can be caused by self-merging and reconnection of a vortex helix with the formation of a vortex ring. The vortex ring moves along the wall of the draft tube and generates a sharp pressure pulse that is registered by pressure transducer. This phenomenon was investigated on a simplified draft tube model using a swirl generator consisting of a stationary swirler and a freely rotating runner. The experiments were performed at Reynolds number (Re) = 10^5. The measurements involved a high-speed visualization technique synchronized with pressure measurements on the draft tube wall, which enables an analysis of the key stages of vortex ring formation by comparing it with the pressure on the draft tube wall. Quantitative information regarding the average velocity distribution was obtained via the LDA technique.
TOPICS: Pressure, Shock (Mechanics), Vortices, Ropes, Oscillations, Generators, Hydraulic turbines, Turbines, Visualization, Flow (Dynamics), Pressure measurement, Reynolds number, Pressure transducers, Stress
research-article  
Felipe A. González Cornejo, Marcela A. Cruchaga and Diego Celentano
J. Fluids Eng   doi: 10.1115/1.4036247
In this work, we propose a fixed mesh finite element formulation to solve the fluid dynamic on an Eulerian mesh dealing with immersed bodies in motion. The study is focused on the computation of the fluid dynamic forces acting on immersed bodies which strongly depend on the evolution of the vortex shedding. The frequency of vortex detachment for flow past cylinder problems can be modified when the cylinder moves promoting the modification of the wake of vortices. Synchronization phenomena appear when the frequencies of the resulting flow pattern coincide with the frequency of the imposed body motion. To study this problem, we propose to describe the immersed body surface by a collection of markers that moves according to the imposed body motion. The markers are updated using a Lagrangian scheme. In this framework, a distinct aspect of the present work is the imposition of the body velocity as an internal immersed boundary condition for the fluid dynamic analysis. To transfer the body velocity to the fluid along the fluid-solid interface, a restriction on the flow velocity is added into the weak form of the Navier-Stokes equations by means of a penalty technique. This work encompasses the study of flows past a cross-flow, streamwise and rotational oscillating cylinders. The results are satisfactorily compared with numerical data reported in the literature, showing a proper behavior for the analysis of long term vibrating systems at low Reynolds numbers.
TOPICS: Flow (Dynamics), Finite element analysis, Cylinders, Fluids, Vortices, Boundary-value problems, Computation, Reynolds number, Wakes, Fluid-dynamic forces, Navier-Stokes equations, Dynamic analysis, Synchronization, Vortex shedding, Cross-flow
research-article  
Somnath Bhattacharyya and Naren Bag
J. Fluids Eng   doi: 10.1115/1.4036265
In this paper we have analyzed an enhanced electroosmotic flow (EOF) by geometric modulation of the surface of a charged nano-channel. Otherwise flat walls of the channel are modulated by embedding rectangular grooves placed perpendicular to the direction of the applied electric field in a periodic manner. The modulated channel is filled with a single electrolyte. The electroosmotic flow within the modulated channel is determined by computing the Navier-Stokes-Nernst-Planck-Poisson equations for a wide range of Debye length. The objective of the present study is to achieve an enhanced EOF in the surface modulated channel. A significant enhancement in average EOF is found for a particular arrangement of grooves with the width of the grooves much higher than its depth and the Debye length is in the order of the channel height. However, the formation of vortex inside the narrow grooves can reduce the EOF when the groove depth is in the order of its width. Results are compared with the cases in which the grooves are replaced by superhydrophobic patches along which a zero shear stress condition is imposed.
TOPICS: Electroosmosis, Vortices, Electrolytes, Shear stress, Electric fields
research-article  
Uriel Goldberg and Paul Batten
J. Fluids Eng   doi: 10.1115/1.4036245
Most literature in the area of turbulent flow over rough surfaces discusses methods for turbulence models based on two or more transport equations, one of which is that for turbulence kinetic energy which supplies k that is heavily used for the rough wall treatment. However, many aeronautical engineers routinely use single equation turbulence models which solve directly for eddy viscosity and do not involve k. The present work proposes methods by which such one-equation models can predict flow cases which include multiple rough surfaces. The current approach does not impose changes to the wall distance function, should such a function be necessary. Several examples show that the proposed method is able to produce good predictions of both skin friction and heat transfer along rough surfaces. While results are not always as accurate as those predicted by turbulence models which solve for k, especially if detached or wake-like flow regions exist, accompanied by significant increase in eddy viscosity, the single-equation models are able to provide predictions at least good enough for preliminary studies.
TOPICS: Turbulence, Surface roughness, Flow (Dynamics), Eddies (Fluid dynamics), Viscosity, Engineers, Kinetic energy, Heat transfer, Skin friction (Fluid dynamics), Wakes
research-article  
Srinivasan Kandaswamy, P.M.V. Subbarao and S.R. Kale
J. Fluids Eng   doi: 10.1115/1.4036249
The present work investigates the extension of Navier-Stokes equations from slip-to-transition regimes with higher order slip boundary condition. To achieve this, a slip model based on the second order slip boundary condition was derived and a special procedure was developed to simulate slip models using FLUENT®. The boundary profile for both top and bottom walls was solved for each pressure ratio by the customized user-defined function and then passed to the FLUENT® solver. The flow characteristics in microchannels of various aspect ratios (a = H / W= 0.002, 0.01 and 0.1) by generating accurate and high resolution experimental data along with the computational validation was studied. For that microchannel system was fabricated in silicon wafers with controlled surface structure and each system has several identical microchannels of same dimensions in parallel and the processed wafer was bonded with a plane wafer. The increased flow rate reduced uncertainty substantially. The experiments were performed up to maximum outlet Knudsen number of 1.01 with nitrogen and the second order slip coefficients were found to be C1 = 1.119 to 1.288 (TMAC = 0.944 to 0.874) and C2 = 0.34.
TOPICS: Gas flow, Silicon, Microchannels, Semiconductor wafers, Flow (Dynamics), Boundary-value problems, Nitrogen, Uncertainty, Dimensions, Pressure, Resolution (Optics), Knudsen number, Navier-Stokes equations
research-article  
Clemens Bernhard Domnick, Dieter Brillert, Christian Musch and Friedrich-Karl Benra
J. Fluids Eng   doi: 10.1115/1.4036263
In steam turbine inlet valves used to adjust the power output of large steam turbines the through-flow is reduced by lowering the valve plug and hence reducing the cross-sectional area between the plug and the seat. At throttled operation a supersonic jet is formed between the plug and the seat. This jet bearing tremendous kinetic energy flows into the valve diffuser where it is dissipated. Depending on the dissipation process a certain portion of the kinetic energy is converted to sound and subsequently to structural vibration, which can be harmful to the valve plug. The flow topology in the valve diffuser has a strong influence on the conversion of kinetic energy to sound and hence vibrations. Several studies show that an annular flow attached to the wall of the valve diffuser causes significantly less noise and vibrations than a detached flow in the core of the diffuser. The relation between the flow topology and the vibrations is already known, but the physics causing the transition from the undesired core flow to the desired annular flow and the dependency on the design are not fully understood. The paper presented here reveals the relation between the flow topology in the steam valve and the separation of underexpanded Coand? wall jets. The physics of the jet separations are clarified and a method to predict the flow separations with a low numerical effort is shown. Based on this safe operational ranges free of separations can be predicted and improved design considerations can be made.
TOPICS: Physics, Stress, Design, Valves, Flow separation, Steam turbines, Flow (Dynamics), Vibration, Diffusers, Topology, Kinetic energy, Steam, Noise (Sound), Bearings, Separation (Technology), Energy dissipation, Jets
research-article  
Sailesh Chitrakar, Hari P. Neopane and Ole G. Dahlhaug
J. Fluids Eng   doi: 10.1115/1.4036269
In Francis turbines, which are normally designed at a reaction ratio of 0.5, the available pressure energy in the fluid is converted into 50% kinetic energy before entering the runner. This causes high acceleration of the flow in guide vanes, which adds to the unsteadiness and losses in the turbine. In sediment affected power plants, the hard sand particles erode and gradually increase the clearance gap between the guide vane and facing plates, which causes more disturbances in downstream turbine components. This study focuses on investigating the flow through the clearance gap of the guide vane with cambered hydrofoil shapes by using Particle Image Velocimetry (PIV) technique. The measurements are carried out in one guide vane cascade rig, which produces similar velocity fields around a guide vane, as compared to the real turbine. The investigation is done in two cases of cambered guide vane NACA profiles and the comparison of the velocity and pressure distribution around the hydrofoil is done with the results in symmetric profile studied earlier. It is seen that the pressure distribution around the hydrofoil affects the velocity field, leakage flow and characteristics of the vortex filament developed inside the cascade. NACA4412, which has flatter suction side than NACA2412 and NACA0012, is seen to have smaller pressure difference between the two adjacent sides of the vane. The flow inside the clearance gap of NACA2412 enforces change in the flow angle, which forms a vortex filament with a rotational component. This vortex along with improper stagnation angle could have greater consequences in the erosion of the runner inlet and more losses of the turbine.
TOPICS: Clearances (Engineering), Hydrofoil, Leakage flows, Guide vanes, Pressure, Flow (Dynamics), Turbines, Vortices, Particulate matter, Cascades (Fluid dynamics), Suction, Kinetic energy, Francis turbines, Sediments, Shapes, Fluids, Sands, Erosion, Plates (structures), Power stations, Turbine components
research-article  
Linsheng Xia, Yongguang Cheng, Zhiyan Yang, Jianfeng You, Jiandong Yang and Zhongdong Qian
J. Fluids Eng   doi: 10.1115/1.4036248
The pressure fluctuations and runner loads on a pump-turbine runner during runaway process are very violent and the corresponding flow evolution is complicated. To study these phenomena and their correlations in depth, the runaway processes of a model pump-turbine at four guide-vane openings (GVOs) were simulated by three-dimensional computational fluid dynamics (3D-CFD). The results show that the flow structures around runner inlet have regular development and transition patterns--the reverse flow occurs when the trajectory moves to the turbine-brake region and the main reverse velocity shifts locations amongst the hub side, the shroud side and the mid-span as the trajectory comes forward and backward in the S-shape region. The locally distributed reverse flow vortex structures (RFVS) enhance the local rotor-stator interaction (RSI) and make the pressure fluctuations in vaneless space at the corresponding section stronger than at the rest sections along the span-wise direction. The transitions of RFVS, turning from the hub side to midspan, facilitate the inception and development of rotating stall, which propagates at approximately 45%-72% of the runner rotation frequency. The evolving rotating stall induces asymmetrical pressure distribution on the runner blade, resulting in intensive fluctuations of runner torque and radial force. During the runaway process, the changing characteristics of the reactive axial force are dominated by the change rate of flow discharge, and the amplitude of low frequency component of axial force are in proportion to the amplitude of discharge change rate.
TOPICS: Pump turbines, Stress, Fluctuations (Physics), Pressure, Flow (Dynamics), Trajectories (Physics), Computational fluid dynamics, Rotors, Turbines, Vortices, Blades, Shapes, Stators, Brakes, Guide vanes, Torque, Rotation
research-article  
Zhi-jiang Jin, Zhi-xin Gao, Ming Zhang and Jin-yuan Qian
J. Fluids Eng   doi: 10.1115/1.4036268
Pilot-Control Globe Valve (PCGV) can use the pressure drop caused by fluid flowing through the orifice located at valve core bottom to open or close the main valve using a small pilot valve. In this paper, Computational Fluid Dynamics (CFD) method is adopted to analyze the pressure drop before and after valve core of PCGV and minor loss of orifice under different structural parameters and inlet velocities, and the simulation results show a good agreement with the experimental results. It turns out that the valve diameters, orifice diameters and pilot pipe diameters have great influences on the pressure drop and the loss coefficient. Moreover, an expression is proposed which can be used to calculate minor loss coefficient, then to estimate the pressure drop and driving force of a PCGV within limited conditions. This paper can be referenced as guidance for deciding the dimension of structural parameters and spring stiffness during design process of a PCGV.
TOPICS: Valves, Pressure drop, Computational fluid dynamics, Design, Pipes, Fluids, Dimensions, Simulation results, Springs, Stiffness
research-article  
Gokturk Memduh Ozkan, Erhan Firat and Huseyin Akilli
J. Fluids Eng   doi: 10.1115/1.4036186
The control of flow in the wake of a circular cylinder by an attached permeable plate having various porosity ratios was analysed experimentally using both Particle Image Velocimetry (PIV) and dye visualization techniques. The force measurements were also done in order to interpret the effect of control method on drag coefficient. The diameter of the cylinder and length to diameter ratio of the plate were kept constant as D= 50 mm and L/D=1.0, respectively. The porosity ratio, ß which can be defined as the ratio of open surface area to the whole body surface area was taken as ß=0.4, 0.5, 0.6, 0.7 and 0.8 (permeable plates). The study was performed considering deep water flow conditions with a constant Reynolds number of ReD = 5000 based on the cylinder diameter. Each permeable plate was attached on the separation point and the results were compared with the results of cylinder without permeable plate (plain cylinder) in order to understand the control effect. Both qualitative and quantitative results revealed that the permeable plates of 0.4=ß=0.6 are effective on controlling the unsteady flow structure downstream of the cylinder, i.e. the vortex formation length was increased, turbulent statistics was reduced and vortex shedding frequency was diminished when the permeable plate attached normal to the cylinder surface from the lower separation point. However the drag force acting on the cylinder was found to be increased due to the increased cross-sectional area.
TOPICS: Separation (Technology), Drag (Fluid dynamics), Circular cylinders, Vortex shedding, Cylinders, Plates (structures), Porosity, Flow (Dynamics), Unsteady flow, Water, Statistics as topic, Visualization, Vortices, Force measurement, Reynolds number, Wakes, Particulate matter, Turbulence

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