In this paper, the lift coefficients of SC-0414 airfoil are estimated by applying modified Yamana’s method to the flow visualization results, which are obtained by utilizing the smoke tunnel. The application of the m...In this paper, the lift coefficients of SC-0414 airfoil are estimated by applying modified Yamana’s method to the flow visualization results, which are obtained by utilizing the smoke tunnel. The application of the modified Yamana’s method is evaluated with two calculation methods. Additionally, the lift estimation, wake measurements, and numerical simulations are performed to clarify the low-speed aerodynamic characteristics of the SC airfoil with flaps. The angle of attack was varied from <span style="white-space:nowrap;">−</span>5<span style="white-space:nowrap;">°</span> to 8<span style="white-space:nowrap;">°</span>. The flow velocity was 12 m/s and the Reynolds number was 1.6 × 10<sup>5</sup>. As a result, the estimated lift coefficients show a good agreement with the results from reference data and numerical simulations. In clean condition, the lift coefficients calculated from the two methods show quantitative agreement, and no significant difference could be confirmed. However, the slope of the lifts calculated from <em>y</em><sub>s</sub> is higher and closer to the reference data than those obtained from s<em>c</em>, where <em>y</em><sub>s</sub> denotes the height where the distance from the streamline to the reference line is the largest, and s<em>c</em> denotes the displacement of the center of pressure from the origin of the coordinate, respectively. In the case of flaps, the GFs have an observable effect on the aerodynamic performance of the SC-0414 airfoil. When the height of the flap was increased, the lift and drag coefficients increased. The installation of a GF with a height equal to 1% of the chord length of the airfoil significantly improved the low-speed aerodynamic performance of SC airfoils.展开更多
A number of piping components in the secondary system of nuclear power plants (NPPs) have been exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, LDIE (Liquid Droplet Impingeme...A number of piping components in the secondary system of nuclear power plants (NPPs) have been exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, LDIE (Liquid Droplet Impingement Erosion), and SPE (Solid Particle Erosion). Those mechanisms may lead to thinning, leaking, or the rupture of components. Due to the pipe ruptures caused by wall thinning of Surry Unit 2 in 1986 and Mihama Unit 3 in 2004, pipe wall thinning management has emerged as one of the most important issues in the nuclear industry. To manage the wall thinning of pipes caused by FAC and erosion, KEPCO-E & C has developed ToSPACE program. It can predict both FAC & erosion phenomena, and also be utilized in the pipe wall thinning management works such as susceptibility analysis, UT (Ultrasonic Test) data evaluation as well as establishment of long-term inspection plan. Even though the ToSPACE can predict the five aging mechanisms mentioned above, only the FAC prediction result using ToSPACE was compared herein with the experimental result using FACTS (Flow Accelerated Corrosion Test System) to verify the ToSPACE’s capability. In addition, the FAC prediction result using ToSPACE was also compared with that of CHECWORKS that is widely used all over the world.展开更多
For Stokes flow in non spherical geometries, when separation of variables fails to derive closed form solutions in a simple product form, analytical solutions can still be obtained in an almost separable form, namely ...For Stokes flow in non spherical geometries, when separation of variables fails to derive closed form solutions in a simple product form, analytical solutions can still be obtained in an almost separable form, namely in semiseparable form, R-separable form or R-semiseparable form. Assuming a stream function Ψ, the axisymmetric viscous Stokes flow is governed by the fourth order elliptic partial differential equation E4Ψ = 0 where E4 = E2oE2 and E2 is the irrotational Stokes operator. Depending on the geometry of the problem, the general solution is given in one of the above separable forms, as series expansions of particular combinations of eigenfunctions that belong to the kernel of the operator E2. In the present manuscript, we provide a review of the methodology and the general solutions of the Stokes equations, for almost any axisymmetric system of coordinates, which are given in a ready to use form. Furthermore, we present necessary and sufficient conditions that are serving as criterion for identifying the kind of the separation the Stokes equation admits, in each axisymmetric coordinate system. Additionally, as an illustration of the usefulness of the obtained analytical solutions, we demonstrate indicatively their application to particular Boundary Value Problems that model medical problems.展开更多
The paper presents the implementation of non-Newtonian fluid properties for compressible multiphase solver in the open source framework OpenFOAM. The transport models for Power Law, Cross Power Law, Casson, Bird-Carre...The paper presents the implementation of non-Newtonian fluid properties for compressible multiphase solver in the open source framework OpenFOAM. The transport models for Power Law, Cross Power Law, Casson, Bird-Carreau and Herschel-Bulkley fluids were included in the thermophysical model library. Appropriate non-Newtonian liquids have been chosen from literature, and pressure driven test simulations are carried out. Therefore, the solver compressibleInterFoam is used to compute air-liquid mixture flows over a backward facing step. A validation of the novel models has been performed by means of a sample-based comparison of the strain rate viscosity relation. The theoretical rheological properties of the selected liquids agree well with the results of the simulated data.展开更多
In this paper, Beltrami vector fields in several orthogonal coordinate systems are obtained analytically and numerically. Specifically, axisymmetric incompressible inviscid steady state Beltrami (Trkalian) fluid flows...In this paper, Beltrami vector fields in several orthogonal coordinate systems are obtained analytically and numerically. Specifically, axisymmetric incompressible inviscid steady state Beltrami (Trkalian) fluid flows are obtained with the motivation to model flows that have been hypothesized to occur in tornadic flows. The studied coordinate systems include those that appear amenable to modeling such flows: the cylindrical, spherical, paraboloidal, and prolate and oblate spheroidal systems. The usual Euler equations are reformulated using the Bragg-Hawthorne equation for the stream function of the flow, which is solved analytically or numerically in each coordinate system under the assumption of separability of variables. Many of the obtained flows are visualized via contour plots of their stream functions in the <em>rz</em>-plane. Finally, the results are combined to provide a qualitative quasi-static model for a progression of tornado-like flows that develop as swirl increases. The results in this paper are equally applicable in electromagnetics, where the equivalent concept is that of a force-free magnetic field.展开更多
Management of various water resources has become a pivotal need for all catchments and sub-catchements in Jordan. Storing treated wastewater applied in reservoirs that originally constructed to store flood and base fl...Management of various water resources has become a pivotal need for all catchments and sub-catchements in Jordan. Storing treated wastewater applied in reservoirs that originally constructed to store flood and base flow water in the country. This practice has proved detrimental to the originally good quality reservoir waters, leading to additional water quality deterioration such as eutrophication issue. Hence, separating treated wastewater from flood and base flow waters to guarantee the availability of better quality waters for higher quality uses such as drinking or recreation. This study focuses on the dams constructed in Kafrain and Shueib catchments, lying west and northwest of Amman. The results of hydrological, hydrogeological, geological, water quality and terrain measurements using Remote Sensing, Geographical Information System (GIS) and Digital Elevation Models (DEM) show that there are nine potential dam sites in the two catchments to construct. In Shueib catchment, two proposed dam sites were selected as suitable dams for fresh water harvesting and groundwater artificial recharge. While, two suggested dam sites are located downstream of Al-Salt and Fuhais wastewater treatment plants for treated wastewater collection. In Kafrain catchment, three proposed dam sites were selected as suitable dams for fresh water harvesting and groundwater artificial recharge. Whereas, two suggested dam sites are located downstream of Wadi Sir wastewater treatment plant, hereby, it can be used to collect the treated wastewater. The study is expected to serve as an example for other catchments in Jordan and elsewhere, especially in water scarcity areas where treated waste water is stored together with flood and base flow waters.展开更多
Local scour downstream of the release structure is a critical problem to the safe and stable operation of water resources and hydropower engineering. In order to investigate the shape and depth of the scour hole under...Local scour downstream of the release structure is a critical problem to the safe and stable operation of water resources and hydropower engineering. In order to investigate the shape and depth of the scour hole under the equilibrium state of erosion and deposition downstream of an apron, a group of 16 experiments from the hydraulic similarity model test of Dangka Hydropower Station?was conducted with the non-cohesive sediment of different median particle sizes under different flow rates in this study. The control variable method was?to?study the influence of the flow rate and sediment size on the shape of the scour hole to define the number of experiment times of each test group. The results showed that the plane shape of the scour hole was irregular ellipse or semi-ellipse. The depth and size of the scour hole increased with the increase of the flow rate, and decreased with the increase of the sediment size;?the downstream longitudinal slope ratio of the scour hole increased with the increase of the sediment size. The coefficients of the upstream and downstream slope ratio of the local scour hole were 1/2 to 1/6 and about 1/10, respectively.展开更多
This study demonstrates an active flow control for deflecting a direction of wake vortex structures behind a NACA0012 airfoil using an active morphing flap. Two-dimensional direct numerical simulations are performed f...This study demonstrates an active flow control for deflecting a direction of wake vortex structures behind a NACA0012 airfoil using an active morphing flap. Two-dimensional direct numerical simulations are performed for flows at the chord Reynolds number of 10,000, and the vortex pattern in the controlled and noncontrolled wakes as well as the effect of an actuation frequency on the control ability are rigorously investigated. It is found that there is an optimum actuation-frequency regime at around <em>F <sup>+</sup></em> = 2.00 which is normalized by the chord length and freestream velocity. The wake vortex pattern of the well-controlled case is classified as the 2P wake pattern according to the Williamson’s categorization [<a href="#ref1">1</a>] [<a href="#ref2">2</a>], where the forced oscillation frequency corresponds to the natural vortex shedding frequency without control. The present classification of wake vortex patterns and finding of the optimum frequency regime in the wake deflection control can lead to a more robust design suitable for vortex-induced-vibration (VIV) related engineering systems.展开更多
Numerical simulations on focused wave propagation are carried out by using three types of numerical models,including the linear potential flow,the nonlinear potential flow and the viscous fluid flow models.The wave-wa...Numerical simulations on focused wave propagation are carried out by using three types of numerical models,including the linear potential flow,the nonlinear potential flow and the viscous fluid flow models.The wave-wave interaction of the focused wave group with different frequency bands and input wave amplitudes is examined,by which the influence of free surface nonlinearity and fluid viscosity on the related phenomenon of focused wave is investigated.The significant influence of free surface nonlinearity on the characteristics of focused wave can be observed,including the increased focused wave crest,delayed focused time and downstream shift of focused position with the increase of input amplitude.It can plot the evident difference between the results of the nonlinear potential flow and linear potential flow models.However,only a little discrepancy between the nonlinear potential flow and viscous fluid flow models can be observed,implying the insignificant effect of fluid viscosity on focused wave behavior.Therefore,the nonlinear potential flow model is recommended for simulating the non-breaking focused wave problem in this study.展开更多
Temperature distribution and variation with time has been considered in the analysis of the influences of the initial level of immersion of a horizontal metallic mesh tube in the liquid on combined buoyant and thermoc...Temperature distribution and variation with time has been considered in the analysis of the influences of the initial level of immersion of a horizontal metallic mesh tube in the liquid on combined buoyant and thermocapillary flow.The combined flow occurs along with the rising liquid film flow on the surface of a horizontal metallic mesh tube.Three different levels of immersion of the metallic mesh tube in the liquid have been tested.Experiments of 60 min in duration have been performed using a heating metallic tube with a diameter of 25 mm and a length of 110 mm,sealed outside with a metallic mesh of 178 mm by 178 mm,and distilled water.These reveal two distinct flow patterns.Thermocouples and infrared thermal imager are utilized to measure the temperature.The level of the liquid free surface relative to the lower edge of the tube is measured as angleθ.The results show that for a smallerθangle,or a low level of immersion,with a relatively low heating power,it is possible to near fully combine the upwards buoyant flow with the rising liquid film flow.In this case,the liquid is heated only in the vicinity of the tube,while the liquid away from the flow region experiences small changes in temperature and the system approaches steady conditions.For largerθangles,or higher levels of immersion,a different flow pattern is noticed on the liquid free surface and identified as the thermo-capillary(Marangoni)flow.The rising liquid film is also present.The higher levels of immersion cause a high temperature gradient in the liquid free surface region and promote thermal stratification;therefore the system could not approach steady conditions.展开更多
The discharge behavior of particles is important in many industrial applications,such as in the core of a pebble bed reactor,which uses a hopper bed filled with many large particles.In this work,a mixture composed of ...The discharge behavior of particles is important in many industrial applications,such as in the core of a pebble bed reactor,which uses a hopper bed filled with many large particles.In this work,a mixture composed of two particle types,freely discharged from a pebble bed,is simulated using the discreteelement method.One is a spherical pebble of diameter equal to that of the fuel pebble of the reactor.The other is a composite particle comprising three spherical pebbles bonded together.The included angleαof the three pebbles characterized the particle conformation,which may affect the discharge behavior of the mixture.The effects of volume fraction of the multi-sphere x(equivalent to the number fraction)on the discharge are also analyzed.Flow patterns,number flow rate,discharge velocity,and mean force of the mixture are computed to help in revealing discharge features.The results show that increasing eitherαor x reduces the discharge flow rate.Fittings and correlations give a quantitative evaluation of the independent effects ofαand x.The analysis of velocity and force explains the mechanism relevant to the main influencing factorsαand x.The results are helpful in gaining a better understanding of the discharge feature of binary mixtures and in providing a quantitative evaluation of the discharge behavior of the reactor core,especially adverse failure conditions.展开更多
The flow structure and geomorphology of rivers are significantly affected by vegetation patterns. In the present study, the effect of vegetation in the form of discontinuous and vertically double layered patches parti...The flow structure and geomorphology of rivers are significantly affected by vegetation patterns. In the present study, the effect of vegetation in the form of discontinuous and vertically double layered patches particularly on the resulting flow turbulence was examined computationally in an open channel. A k-ɛ model was implemented in this research work which was developed using 3-D numerical code FLUENT (ANSYS). After the validation process of numerical model, the impact of discontinuous layered vegetation patches on the flow turbulence was investigated against varying vegetation density and patch length. The mean stream-wise velocities at specified positions showed larger spatial fluctuations directly upstream and downstream of vegetation elements, whereas sharp inflections in the profiles were witnessed at the top of smaller submerged elements i.e. z/hs= 1 (where z is the flow depth and hs is the smaller vegetation height). The reduction in flow velocity due to tall vegetation structure was more as compared with that of short vegetation. The mean velocity in the patch regions was visibly higher than that in the gap regions. The profiles of turbulent flow properties showed more rise and fall within the patches with a high vegetation density i.e. Ss/d= 4;and St/d= 8 (where Ss/d and St/d are the smaller and taller vegetation spacing, while d is the vegetation diameter) as compared with low vegetation density i.e. Ss/d= 8;and St/d= 16. The turbulent flow structure in the large patch and gap regions was found to be more stable than that in the small patches and gaps;whereas, due to the variation in distribution form of the patch, turbulence is relatively unaffected, and the flow structure variation is low. Turbulence was observed to be large, followed by a saw-tooth distribution within the patches;whereas, low turbulence is observed in the non-vegetation regions. The turbulent intensity acquired maximum of 13% turbulence for dense vegetation arrangement as compared to that of sparse arrangement having maximum of 展开更多
In the current study,thermal boundary conditions are considered in a rotating smooth channel with a square cross-section to investigate the secondary flow and compare it to that of the same channel without heating.The...In the current study,thermal boundary conditions are considered in a rotating smooth channel with a square cross-section to investigate the secondary flow and compare it to that of the same channel without heating.The measurement is conducted at three streamwise planes(X=445 mm,525 mm,605 mm).The flow parameters are the Reynolds number(Re=4750,which was based on the average longitudinal or primary velocity U and the hydraulic diameter D of the channel cross-section),the rotation number(Ro=?D/U,where?is the rotational velocity,ranging from 0 to 0.26),and the aspect ratio of the channel cross-section(AR=1,which is calculated by dividing the channel height by the channel width).The leading and trailing walls are heated under a constant heat flux q_w=380 W/m~2,and the top and bottom walls are isothermal at room temperature.This work is in a series with our previous work without thermal boundary conditions.Based on the experimental data,we obtained a four-vortex regime.There is a counter-rotating vortex pair near the leading side and the trailing side.Because the leading and trailing walls are heated,the buoyancy force increases the relative vertical position of the vortex pair near the trailing side from 5%to 12.5%of the hydraulic diameter.When moving upstream along the streamwise direction,the upper vortex near the trailing wall becomes weaker,whereas the lower vortex becomes stronger.As the rotational speed increases,the vortex pair near the trailing side is inhibited by the Coriolis force.Under heated thermal boundary conditions,the vortex pair near the trailing side reappears due to the effect of buoyancy force.These results indicate that the buoyancy force has a substantial effect on the secondary flow regime under thermal boundary conditions.展开更多
Plane, transverse MHD flow through a porous structure is considered in this work. Solution to the governing equations is obtained using an inverse method in which the streamfunction of the flow is considered linear in...Plane, transverse MHD flow through a porous structure is considered in this work. Solution to the governing equations is obtained using an inverse method in which the streamfunction of the flow is considered linear in one of the space variables. Expressions for flow quantities are obtained for finitely conducting and infinitely conducting fluids.展开更多
In this study, we apply the optical flow method to the time-series shadowgraph images of impinging jets using a high-speed video camera with high spatial and temporal resolution. This image analysis provides quantitat...In this study, we apply the optical flow method to the time-series shadowgraph images of impinging jets using a high-speed video camera with high spatial and temporal resolution. This image analysis provides quantitative velocity vector fields in the object space without tracer particles. The analysis results clearly capture the details of the coherent vortex structure and its advection from the shear layer of the free jet. Although the results still leave challenges for the quantitative validation, the results show that this analysis method is effective for understanding the details of the physical phenomenon based on the quantitative values extracted from the shadowgraph images.展开更多
Presence of a cavity changes the mean and fluctuating pressure distributions inside and near the cavity.For cylindrical cavity flow,the diameter-to-depth ratio is the dominant factor.In this study,flow is naturally de...Presence of a cavity changes the mean and fluctuating pressure distributions inside and near the cavity.For cylindrical cavity flow,the diameter-to-depth ratio is the dominant factor.In this study,flow is naturally developed along a flat plate with two different lengths,resulting in different incoming boundary layer thicknesses ahead of the cavity.The effect of Reynolds number based on incoming boundary layer thickness on characteristics of mean and fluctuating pressure distributions is addressed.Pressure sensitive paint was also used to visualize the mean surface pressure patterns.The effect of Reynolds number on the classification of compressible cylindrical cavity flow and self-sustained oscillating frequency is not significant.An increase in Reynolds number results in a reduction in the value of differential pressure or momentum flux near the rear edge.展开更多
The delayed detached-eddy simulation with adaptive coefficient(DDES-AC)method is used to simulate the baseline and leading-edge undulation control of dynamic stall for the reverse flow past a finite-span wing with NAC...The delayed detached-eddy simulation with adaptive coefficient(DDES-AC)method is used to simulate the baseline and leading-edge undulation control of dynamic stall for the reverse flow past a finite-span wing with NACA0012 airfoil.The numerical results of the baseline configuration are compared with available measurements.DDES and DDES-AC perform differently when predicting the primary and secondary dynamic stalls.Overall,DDES-AC performs better owing to the decrease of grey area between the strong shear layer and the fully three-dimensional separated flow.Moreover,the effects of the undulating leading-edge on the forces,lift gradients,and instantaneous flow structures are explored.Compared with the uncontrolled case,the lift gradient in the primary dynamic stall is reduced from 18.4 to 8.5,and the secondary dynamic stall disappears.Therefore,periodic unsteady air-loads are also reduced.Additionally,the control mechanism of the wavy leading edge(WLE)is also investigated by comparison with the straight leading edge(SLE).No sudden breakdown of strong vortices is the main cause for WLE control.展开更多
Background: A Randomized Controlled Trial (RCT) has been elaborated where goal directed fluid and hemodynamic therapy (GDFHT) will be realized with trans-thoracic echocardiographic aortic blood flow peak velocity vari...Background: A Randomized Controlled Trial (RCT) has been elaborated where goal directed fluid and hemodynamic therapy (GDFHT) will be realized with trans-thoracic echocardiographic aortic blood flow peak velocity variation (ΔVpeak) and distance minute (DM) to guide fluid therapy and hemodynamics in high risk pediatric surgical patients. This RCT will clarify the impact of GDFHT with ΔVpeak and DM on postoperative outcome in terms of morbidity, length of stay in the intensive care unit (LOSICU), length of mechanical ventilation (LMV) and length of hospital stay (LOS) in children. To determine values of ΔVpeak, DM and VTI predictive of these postoperative outcomes, an observational pilot study will be realized. This pilot study is described here. The primary objective of this study is to determine values of ΔVpeak, DM and ITV predictive of postoperative outcome in children in terms of morbidity. The secondary objectives are to determine values of ΔVpeak, DM and ITV predictive of LOSICU, LMV, LOS, intraoperative, postoperative fluid administration and vasoactive-inotropic therapy. Methods: 500 - 1000 children aged less than 18 years will be included prospectively. Statistic analysis will be realized with XLSTAT 2019.4.2 software or plus. Results and Conclusions: This trial protocol will determine values of ΔVpeak, DM and ITV with echocardiography predictive of postoperative outcome in children.展开更多
Taking into account the startup behaviour of following vehicles in the waiting area of urban traffic signal, we propose an extended Nagel-Schreckenberg model for single-lane traffic flow, in which the dynamic behavior...Taking into account the startup behaviour of following vehicles in the waiting area of urban traffic signal, we propose an extended Nagel-Schreckenberg model for single-lane traffic flow, in which the dynamic behavior of each vehicle depends on not only its own headway but also the headway of the immediately preceding one. The numerical simulation of the present model reproduces some complicated nonlinear phenomena observed in real traffic such as free flow, ghostly blockage, synchronized flow and so on. For specific parameter combinations the flow-density relation of this model shows two meta-stable branches near the transition density from free flow to wide moving traffic jam. Finally, the analytical results of the model under some specific parameters are given by using the mean field theory.展开更多
文摘In this paper, the lift coefficients of SC-0414 airfoil are estimated by applying modified Yamana’s method to the flow visualization results, which are obtained by utilizing the smoke tunnel. The application of the modified Yamana’s method is evaluated with two calculation methods. Additionally, the lift estimation, wake measurements, and numerical simulations are performed to clarify the low-speed aerodynamic characteristics of the SC airfoil with flaps. The angle of attack was varied from <span style="white-space:nowrap;">−</span>5<span style="white-space:nowrap;">°</span> to 8<span style="white-space:nowrap;">°</span>. The flow velocity was 12 m/s and the Reynolds number was 1.6 × 10<sup>5</sup>. As a result, the estimated lift coefficients show a good agreement with the results from reference data and numerical simulations. In clean condition, the lift coefficients calculated from the two methods show quantitative agreement, and no significant difference could be confirmed. However, the slope of the lifts calculated from <em>y</em><sub>s</sub> is higher and closer to the reference data than those obtained from s<em>c</em>, where <em>y</em><sub>s</sub> denotes the height where the distance from the streamline to the reference line is the largest, and s<em>c</em> denotes the displacement of the center of pressure from the origin of the coordinate, respectively. In the case of flaps, the GFs have an observable effect on the aerodynamic performance of the SC-0414 airfoil. When the height of the flap was increased, the lift and drag coefficients increased. The installation of a GF with a height equal to 1% of the chord length of the airfoil significantly improved the low-speed aerodynamic performance of SC airfoils.
文摘A number of piping components in the secondary system of nuclear power plants (NPPs) have been exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, LDIE (Liquid Droplet Impingement Erosion), and SPE (Solid Particle Erosion). Those mechanisms may lead to thinning, leaking, or the rupture of components. Due to the pipe ruptures caused by wall thinning of Surry Unit 2 in 1986 and Mihama Unit 3 in 2004, pipe wall thinning management has emerged as one of the most important issues in the nuclear industry. To manage the wall thinning of pipes caused by FAC and erosion, KEPCO-E & C has developed ToSPACE program. It can predict both FAC & erosion phenomena, and also be utilized in the pipe wall thinning management works such as susceptibility analysis, UT (Ultrasonic Test) data evaluation as well as establishment of long-term inspection plan. Even though the ToSPACE can predict the five aging mechanisms mentioned above, only the FAC prediction result using ToSPACE was compared herein with the experimental result using FACTS (Flow Accelerated Corrosion Test System) to verify the ToSPACE’s capability. In addition, the FAC prediction result using ToSPACE was also compared with that of CHECWORKS that is widely used all over the world.
文摘For Stokes flow in non spherical geometries, when separation of variables fails to derive closed form solutions in a simple product form, analytical solutions can still be obtained in an almost separable form, namely in semiseparable form, R-separable form or R-semiseparable form. Assuming a stream function Ψ, the axisymmetric viscous Stokes flow is governed by the fourth order elliptic partial differential equation E4Ψ = 0 where E4 = E2oE2 and E2 is the irrotational Stokes operator. Depending on the geometry of the problem, the general solution is given in one of the above separable forms, as series expansions of particular combinations of eigenfunctions that belong to the kernel of the operator E2. In the present manuscript, we provide a review of the methodology and the general solutions of the Stokes equations, for almost any axisymmetric system of coordinates, which are given in a ready to use form. Furthermore, we present necessary and sufficient conditions that are serving as criterion for identifying the kind of the separation the Stokes equation admits, in each axisymmetric coordinate system. Additionally, as an illustration of the usefulness of the obtained analytical solutions, we demonstrate indicatively their application to particular Boundary Value Problems that model medical problems.
文摘The paper presents the implementation of non-Newtonian fluid properties for compressible multiphase solver in the open source framework OpenFOAM. The transport models for Power Law, Cross Power Law, Casson, Bird-Carreau and Herschel-Bulkley fluids were included in the thermophysical model library. Appropriate non-Newtonian liquids have been chosen from literature, and pressure driven test simulations are carried out. Therefore, the solver compressibleInterFoam is used to compute air-liquid mixture flows over a backward facing step. A validation of the novel models has been performed by means of a sample-based comparison of the strain rate viscosity relation. The theoretical rheological properties of the selected liquids agree well with the results of the simulated data.
文摘In this paper, Beltrami vector fields in several orthogonal coordinate systems are obtained analytically and numerically. Specifically, axisymmetric incompressible inviscid steady state Beltrami (Trkalian) fluid flows are obtained with the motivation to model flows that have been hypothesized to occur in tornadic flows. The studied coordinate systems include those that appear amenable to modeling such flows: the cylindrical, spherical, paraboloidal, and prolate and oblate spheroidal systems. The usual Euler equations are reformulated using the Bragg-Hawthorne equation for the stream function of the flow, which is solved analytically or numerically in each coordinate system under the assumption of separability of variables. Many of the obtained flows are visualized via contour plots of their stream functions in the <em>rz</em>-plane. Finally, the results are combined to provide a qualitative quasi-static model for a progression of tornado-like flows that develop as swirl increases. The results in this paper are equally applicable in electromagnetics, where the equivalent concept is that of a force-free magnetic field.
文摘Management of various water resources has become a pivotal need for all catchments and sub-catchements in Jordan. Storing treated wastewater applied in reservoirs that originally constructed to store flood and base flow water in the country. This practice has proved detrimental to the originally good quality reservoir waters, leading to additional water quality deterioration such as eutrophication issue. Hence, separating treated wastewater from flood and base flow waters to guarantee the availability of better quality waters for higher quality uses such as drinking or recreation. This study focuses on the dams constructed in Kafrain and Shueib catchments, lying west and northwest of Amman. The results of hydrological, hydrogeological, geological, water quality and terrain measurements using Remote Sensing, Geographical Information System (GIS) and Digital Elevation Models (DEM) show that there are nine potential dam sites in the two catchments to construct. In Shueib catchment, two proposed dam sites were selected as suitable dams for fresh water harvesting and groundwater artificial recharge. While, two suggested dam sites are located downstream of Al-Salt and Fuhais wastewater treatment plants for treated wastewater collection. In Kafrain catchment, three proposed dam sites were selected as suitable dams for fresh water harvesting and groundwater artificial recharge. Whereas, two suggested dam sites are located downstream of Wadi Sir wastewater treatment plant, hereby, it can be used to collect the treated wastewater. The study is expected to serve as an example for other catchments in Jordan and elsewhere, especially in water scarcity areas where treated waste water is stored together with flood and base flow waters.
文摘Local scour downstream of the release structure is a critical problem to the safe and stable operation of water resources and hydropower engineering. In order to investigate the shape and depth of the scour hole under the equilibrium state of erosion and deposition downstream of an apron, a group of 16 experiments from the hydraulic similarity model test of Dangka Hydropower Station?was conducted with the non-cohesive sediment of different median particle sizes under different flow rates in this study. The control variable method was?to?study the influence of the flow rate and sediment size on the shape of the scour hole to define the number of experiment times of each test group. The results showed that the plane shape of the scour hole was irregular ellipse or semi-ellipse. The depth and size of the scour hole increased with the increase of the flow rate, and decreased with the increase of the sediment size;?the downstream longitudinal slope ratio of the scour hole increased with the increase of the sediment size. The coefficients of the upstream and downstream slope ratio of the local scour hole were 1/2 to 1/6 and about 1/10, respectively.
文摘This study demonstrates an active flow control for deflecting a direction of wake vortex structures behind a NACA0012 airfoil using an active morphing flap. Two-dimensional direct numerical simulations are performed for flows at the chord Reynolds number of 10,000, and the vortex pattern in the controlled and noncontrolled wakes as well as the effect of an actuation frequency on the control ability are rigorously investigated. It is found that there is an optimum actuation-frequency regime at around <em>F <sup>+</sup></em> = 2.00 which is normalized by the chord length and freestream velocity. The wake vortex pattern of the well-controlled case is classified as the 2P wake pattern according to the Williamson’s categorization [<a href="#ref1">1</a>] [<a href="#ref2">2</a>], where the forced oscillation frequency corresponds to the natural vortex shedding frequency without control. The present classification of wake vortex patterns and finding of the optimum frequency regime in the wake deflection control can lead to a more robust design suitable for vortex-induced-vibration (VIV) related engineering systems.
基金the National Natural Science Foundation of China(Grant Nos.51909027 and 51679035),the Project of Educational Commission of Liaoning Province(Grant No.L201601),the High-Level Innovation and Entrepreneurship Team of Liaoning Province(Grant No.XLYC1908027),the Fundamental Research Funds for the Central Universities(Grant No.DUT2017TB05).
文摘Numerical simulations on focused wave propagation are carried out by using three types of numerical models,including the linear potential flow,the nonlinear potential flow and the viscous fluid flow models.The wave-wave interaction of the focused wave group with different frequency bands and input wave amplitudes is examined,by which the influence of free surface nonlinearity and fluid viscosity on the related phenomenon of focused wave is investigated.The significant influence of free surface nonlinearity on the characteristics of focused wave can be observed,including the increased focused wave crest,delayed focused time and downstream shift of focused position with the increase of input amplitude.It can plot the evident difference between the results of the nonlinear potential flow and linear potential flow models.However,only a little discrepancy between the nonlinear potential flow and viscous fluid flow models can be observed,implying the insignificant effect of fluid viscosity on focused wave behavior.Therefore,the nonlinear potential flow model is recommended for simulating the non-breaking focused wave problem in this study.
基金supported by Science and Technology Development Program of Qinghai Province(2013-N-547).
文摘Temperature distribution and variation with time has been considered in the analysis of the influences of the initial level of immersion of a horizontal metallic mesh tube in the liquid on combined buoyant and thermocapillary flow.The combined flow occurs along with the rising liquid film flow on the surface of a horizontal metallic mesh tube.Three different levels of immersion of the metallic mesh tube in the liquid have been tested.Experiments of 60 min in duration have been performed using a heating metallic tube with a diameter of 25 mm and a length of 110 mm,sealed outside with a metallic mesh of 178 mm by 178 mm,and distilled water.These reveal two distinct flow patterns.Thermocouples and infrared thermal imager are utilized to measure the temperature.The level of the liquid free surface relative to the lower edge of the tube is measured as angleθ.The results show that for a smallerθangle,or a low level of immersion,with a relatively low heating power,it is possible to near fully combine the upwards buoyant flow with the rising liquid film flow.In this case,the liquid is heated only in the vicinity of the tube,while the liquid away from the flow region experiences small changes in temperature and the system approaches steady conditions.For largerθangles,or higher levels of immersion,a different flow pattern is noticed on the liquid free surface and identified as the thermo-capillary(Marangoni)flow.The rising liquid film is also present.The higher levels of immersion cause a high temperature gradient in the liquid free surface region and promote thermal stratification;therefore the system could not approach steady conditions.
基金The authors are grateful for research support from the National Natural Science Foundation of China(Grant No.51576211)the Sci-ence Fund for Creative Research Groups of National Natural Science Foundation of China(Grant No.51621062)and the National High Technology Research and Development Program of China(863)(2014AA052701).
文摘The discharge behavior of particles is important in many industrial applications,such as in the core of a pebble bed reactor,which uses a hopper bed filled with many large particles.In this work,a mixture composed of two particle types,freely discharged from a pebble bed,is simulated using the discreteelement method.One is a spherical pebble of diameter equal to that of the fuel pebble of the reactor.The other is a composite particle comprising three spherical pebbles bonded together.The included angleαof the three pebbles characterized the particle conformation,which may affect the discharge behavior of the mixture.The effects of volume fraction of the multi-sphere x(equivalent to the number fraction)on the discharge are also analyzed.Flow patterns,number flow rate,discharge velocity,and mean force of the mixture are computed to help in revealing discharge features.The results show that increasing eitherαor x reduces the discharge flow rate.Fittings and correlations give a quantitative evaluation of the independent effects ofαand x.The analysis of velocity and force explains the mechanism relevant to the main influencing factorsαand x.The results are helpful in gaining a better understanding of the discharge feature of binary mixtures and in providing a quantitative evaluation of the discharge behavior of the reactor core,especially adverse failure conditions.
文摘The flow structure and geomorphology of rivers are significantly affected by vegetation patterns. In the present study, the effect of vegetation in the form of discontinuous and vertically double layered patches particularly on the resulting flow turbulence was examined computationally in an open channel. A k-ɛ model was implemented in this research work which was developed using 3-D numerical code FLUENT (ANSYS). After the validation process of numerical model, the impact of discontinuous layered vegetation patches on the flow turbulence was investigated against varying vegetation density and patch length. The mean stream-wise velocities at specified positions showed larger spatial fluctuations directly upstream and downstream of vegetation elements, whereas sharp inflections in the profiles were witnessed at the top of smaller submerged elements i.e. z/hs= 1 (where z is the flow depth and hs is the smaller vegetation height). The reduction in flow velocity due to tall vegetation structure was more as compared with that of short vegetation. The mean velocity in the patch regions was visibly higher than that in the gap regions. The profiles of turbulent flow properties showed more rise and fall within the patches with a high vegetation density i.e. Ss/d= 4;and St/d= 8 (where Ss/d and St/d are the smaller and taller vegetation spacing, while d is the vegetation diameter) as compared with low vegetation density i.e. Ss/d= 8;and St/d= 16. The turbulent flow structure in the large patch and gap regions was found to be more stable than that in the small patches and gaps;whereas, due to the variation in distribution form of the patch, turbulence is relatively unaffected, and the flow structure variation is low. Turbulence was observed to be large, followed by a saw-tooth distribution within the patches;whereas, low turbulence is observed in the non-vegetation regions. The turbulent intensity acquired maximum of 13% turbulence for dense vegetation arrangement as compared to that of sparse arrangement having maximum of
基金financially supported by the National Natural Science Foundation of China(No.51822602)the Fundamental Research Funds for the Central Universities(No.YWF-19-BJ-J-293)。
文摘In the current study,thermal boundary conditions are considered in a rotating smooth channel with a square cross-section to investigate the secondary flow and compare it to that of the same channel without heating.The measurement is conducted at three streamwise planes(X=445 mm,525 mm,605 mm).The flow parameters are the Reynolds number(Re=4750,which was based on the average longitudinal or primary velocity U and the hydraulic diameter D of the channel cross-section),the rotation number(Ro=?D/U,where?is the rotational velocity,ranging from 0 to 0.26),and the aspect ratio of the channel cross-section(AR=1,which is calculated by dividing the channel height by the channel width).The leading and trailing walls are heated under a constant heat flux q_w=380 W/m~2,and the top and bottom walls are isothermal at room temperature.This work is in a series with our previous work without thermal boundary conditions.Based on the experimental data,we obtained a four-vortex regime.There is a counter-rotating vortex pair near the leading side and the trailing side.Because the leading and trailing walls are heated,the buoyancy force increases the relative vertical position of the vortex pair near the trailing side from 5%to 12.5%of the hydraulic diameter.When moving upstream along the streamwise direction,the upper vortex near the trailing wall becomes weaker,whereas the lower vortex becomes stronger.As the rotational speed increases,the vortex pair near the trailing side is inhibited by the Coriolis force.Under heated thermal boundary conditions,the vortex pair near the trailing side reappears due to the effect of buoyancy force.These results indicate that the buoyancy force has a substantial effect on the secondary flow regime under thermal boundary conditions.
文摘Plane, transverse MHD flow through a porous structure is considered in this work. Solution to the governing equations is obtained using an inverse method in which the streamfunction of the flow is considered linear in one of the space variables. Expressions for flow quantities are obtained for finitely conducting and infinitely conducting fluids.
文摘In this study, we apply the optical flow method to the time-series shadowgraph images of impinging jets using a high-speed video camera with high spatial and temporal resolution. This image analysis provides quantitative velocity vector fields in the object space without tracer particles. The analysis results clearly capture the details of the coherent vortex structure and its advection from the shear layer of the free jet. Although the results still leave challenges for the quantitative validation, the results show that this analysis method is effective for understanding the details of the physical phenomenon based on the quantitative values extracted from the shadowgraph images.
基金financial support from the Ministry of Science and Technology,Taiwan,China(MOST 1032923-E-006-006-MY3).
文摘Presence of a cavity changes the mean and fluctuating pressure distributions inside and near the cavity.For cylindrical cavity flow,the diameter-to-depth ratio is the dominant factor.In this study,flow is naturally developed along a flat plate with two different lengths,resulting in different incoming boundary layer thicknesses ahead of the cavity.The effect of Reynolds number based on incoming boundary layer thickness on characteristics of mean and fluctuating pressure distributions is addressed.Pressure sensitive paint was also used to visualize the mean surface pressure patterns.The effect of Reynolds number on the classification of compressible cylindrical cavity flow and self-sustained oscillating frequency is not significant.An increase in Reynolds number results in a reduction in the value of differential pressure or momentum flux near the rear edge.
基金the National Natural Science Foundation of China(Grants 91852113 and 11772174,and 91952302),National Key Project(Grant GJXM92579)the National Key R&D Program of China(Grant 2019YFA0405302)the authors would like to express their gratitude to Tsinghua National Laboratory for Information Science and Tech no logy for computation resources.
文摘The delayed detached-eddy simulation with adaptive coefficient(DDES-AC)method is used to simulate the baseline and leading-edge undulation control of dynamic stall for the reverse flow past a finite-span wing with NACA0012 airfoil.The numerical results of the baseline configuration are compared with available measurements.DDES and DDES-AC perform differently when predicting the primary and secondary dynamic stalls.Overall,DDES-AC performs better owing to the decrease of grey area between the strong shear layer and the fully three-dimensional separated flow.Moreover,the effects of the undulating leading-edge on the forces,lift gradients,and instantaneous flow structures are explored.Compared with the uncontrolled case,the lift gradient in the primary dynamic stall is reduced from 18.4 to 8.5,and the secondary dynamic stall disappears.Therefore,periodic unsteady air-loads are also reduced.Additionally,the control mechanism of the wavy leading edge(WLE)is also investigated by comparison with the straight leading edge(SLE).No sudden breakdown of strong vortices is the main cause for WLE control.
文摘Background: A Randomized Controlled Trial (RCT) has been elaborated where goal directed fluid and hemodynamic therapy (GDFHT) will be realized with trans-thoracic echocardiographic aortic blood flow peak velocity variation (ΔVpeak) and distance minute (DM) to guide fluid therapy and hemodynamics in high risk pediatric surgical patients. This RCT will clarify the impact of GDFHT with ΔVpeak and DM on postoperative outcome in terms of morbidity, length of stay in the intensive care unit (LOSICU), length of mechanical ventilation (LMV) and length of hospital stay (LOS) in children. To determine values of ΔVpeak, DM and VTI predictive of these postoperative outcomes, an observational pilot study will be realized. This pilot study is described here. The primary objective of this study is to determine values of ΔVpeak, DM and ITV predictive of postoperative outcome in children in terms of morbidity. The secondary objectives are to determine values of ΔVpeak, DM and ITV predictive of LOSICU, LMV, LOS, intraoperative, postoperative fluid administration and vasoactive-inotropic therapy. Methods: 500 - 1000 children aged less than 18 years will be included prospectively. Statistic analysis will be realized with XLSTAT 2019.4.2 software or plus. Results and Conclusions: This trial protocol will determine values of ΔVpeak, DM and ITV with echocardiography predictive of postoperative outcome in children.
文摘Taking into account the startup behaviour of following vehicles in the waiting area of urban traffic signal, we propose an extended Nagel-Schreckenberg model for single-lane traffic flow, in which the dynamic behavior of each vehicle depends on not only its own headway but also the headway of the immediately preceding one. The numerical simulation of the present model reproduces some complicated nonlinear phenomena observed in real traffic such as free flow, ghostly blockage, synchronized flow and so on. For specific parameter combinations the flow-density relation of this model shows two meta-stable branches near the transition density from free flow to wide moving traffic jam. Finally, the analytical results of the model under some specific parameters are given by using the mean field theory.