scholarly journals Velocity difference changes between fluid and sand particles in boundary-layer and very near wake area

2021 ◽  
Vol 25 (6 Part A) ◽  
pp. 4217-4224
Author(s):  
Sha Sha ◽  
Xiantang Zhang ◽  
Zhiang Wang ◽  
Han Liu ◽  
Huiyao Zhang
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Cylindrical Surface ◽  
Dynamic Pressure ◽  
Fluid Velocity ◽  
Near Wake ◽  
Two Phase ◽  
Velocity Change ◽  
Sand Flow ◽  
Sand Particles

Fluent simulates the water-sand flow around a cylinder. Monitoring lines are set up at different positions in the cylindrical surface and the very near wake area behind the cylinder, in order to explore the speed difference of fluid and sand in the water-sand two-phase flow in the boundary-layer and the very near wake area. The results show that the sand particles stay for the longest time on the back of the cylindrical surface and in the very near wake area, and a small part of the sand particles are sticky on the back of the cylindrical pier. When the height of the cylinder is z/D ? (1.57, 3.14), the turbulent flow on the cylindrical surface is fully developed. The dynamic pressure of the flow field in the very near wake area be-hind the cylinder fluctuates greatly, and the water-sand flow is extremely unstable. At the monitoring position of the cylinder, there is a sudden decrease in the velocity of the fluid, while the velocity of the sand particles changes little and remains finally at about -0.02 m/s. The water-sand flow field near the wall changes drastically, but the velocity change of sand particles has obvious hysteresis compared with fluid. When leaving the near-wall position but still in the cylindrical wake area (x/D ? 3), the changes in the water-sand flow field are more intense and the velocity of the sand particles is still slightly larger than the fluid velocity.

Wind Tunnel Experiments on How a Porous Fence Affects Flow and Erosion on Sand Dune

2010 ◽  
Author(s):  
Daisuke Aoshima ◽  
Itsuki Nakamura ◽  
Yusuke Sakamoto ◽  
Takahiro Tsukahara ◽  
Makoto Yamamoto ◽  
...  
Keyword(s):  
Flow Field ◽  
Sand Dune ◽  
Phase Flow ◽  
Erosion Process ◽  
Wind Tunnel Experiments ◽  
Two Phase ◽  
Combating Desertification ◽  
Sand Movement ◽  
Sand Particles ◽  
Porous Fence

For the purpose of combating desertification, it is important to understand mechanisms of the wind-blown sand movement, which is essentially a complicated two-phase flow phenomenon of sand particles and air. Therefore, we investigated the flow field around a model dune and the erosion process of the dune. In this study, we employed a porous fence, which was installed on the model dune, and examined its effect on the sand movement. The erosion process and its relationship with the turbulent intensity and the flow around the dune were discussed focusing on dependence of the flow field on the fence porosity. We tested four types of porous fences, which had different porosities: 0% (no permeability), 10%, 30%, and 50%. How a position of the fence affects suppression of the dune erosion was also examined. In the present experimental range, it can be concluded that the most effective fence position to suppress the sand movement should depend on porosity of the fence.

Mass Flux and Hydrodynamic Forces of Two-Phase Cavitating Flow Through a Safety Relief Valve at Initial Subcooling Conditions

2014 ◽  
Author(s):  
Jorge Pinho ◽  
Patrick Rambaud ◽  
Saïd Chabane
Keyword(s):  
Mass Flux ◽  
Dynamic Pressure ◽  
Fluid Velocity ◽  
Flow Characteristics ◽  
Relief Valve ◽  
Two Phase ◽  
Fluid Forces ◽  
Flow Through ◽  
Phase Mixture ◽  
Local Speed

Previous experiments were conducted and reported in a safety relief valve. It was noticed that in presence of a cavitating two-phase flow, the mass flux tends to be reduced due to the two-phase mixture compressibility. Moreover, the forces acting on the valve are dependent on the dynamic pressure and therefore, characteristics may be affected by the presence of a gas phase. The goal of this study is to propose a mathematical model capable of predicting the mass flux and forces acting on a safety relief valve experiencing cavitation at initial high subcooling conditions. For the mass flux prediction, an extension of the actual recommended sizing equations of IEC 60534-2-3 is proposed, including a formulation of the semi-critical region based on the hypothesis that compressibility of a two-phase mixture may be considered as an ellipse. It is verified that at chocking flow conditions, the critical section is partially filled by vapor as the fluid velocity equals the local speed of sound. Finally, a theoretical analysis is proposed to estimate the hydrodynamic fluid forces acting on the disk of a safety relief valve, using a simplified axisymmetric system of a plate over a nozzle. Results show a good agreement against experimental data and underline the influence of the backpressure in the SRV flow characteristics.

Numerical Investigation of Scour Beneath a Subsea Piggyback Pipeline

2020 ◽  
Author(s):  
Jun Huang ◽  
Guang Yin ◽  
Muk Chen Ong ◽  
Xu Jia
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Kinetic Theory ◽  
Boundary Layer Flow ◽  
Granular Flow ◽  
Scour Depth ◽  
Two Dimensional ◽  
Two Phase ◽  
Binary Collisions ◽  
Layer Flow

Abstract In present study, two-dimensional numerical simulations have been carried out to investigate scour beneath a piggyback pipeline subjected to a subsea boundary layer flow using SedFoam (an open-source multi-dimensional Eulerian two-phase solver for sediment transport based on OpenFOAM). In the piggyback configuration, a small pipeline is attached on the upstream and downstream sides of a large pipeline. This form of piggyback can reduce the scour depth beneath the pipeline (Yang et al., 2019). In the solver, the turbulence Reynolds stress is resolved using a two-phase modified k-ε model. The particle stresses caused by the binary collisions and contacts are modeled by the kinetic theory for granular flow and a phenomenological frictional model, respectively. The effects of the locations of the small pipelines attached on the large pipeline on the scour and the surrounding flow field are discussed.

Characteristics of the Flow Past a Wall-Mounted Finite-Length Square Cylinder at Low Reynolds Number With Varying Boundary Layer Thickness

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Sachidananda Behera ◽  
Arun K. Saha
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Field ◽  
Layer Thickness ◽  
Finite Length ◽  
Boundary Layer Thickness ◽  
Square Cylinder ◽  
Near Wake ◽  
Wall Boundary Layer ◽  
Wall Boundary

Direct numerical simulation (DNS) is performed to investigate the modes of shedding of the wake of a wall-mounted finite-length square cylinder with an aspect ratio (AR) of 7 for six different boundary layer thicknesses (0.0–0.30) at a Reynolds number of 250. For all the cases of wall boundary layer considered in this study, two modes of shedding, namely, anti-symmetric and symmetric modes of shedding, were found to coexist in the cylinder wake with symmetric one occurring intermittently for smaller time duration. The phase-averaged flow field revealed that the symmetric modes of shedding occur only during instances when the near wake experiences the maximum strength of upwash/downwash flow. The boundary layer thickness seems to have a significant effect on the area of dominance of both downwash and upwash flow in instantaneous and time-averaged flow field. It is observed that the near-wake topology and the total drag force acting on the cylinder are significantly affected by the bottom-wall boundary layer thickness. The overall drag coefficient is found to decrease with thickening of the wall boundary layer thickness.

The Numerical Simulation of the Single Abrasive Motion Law in the Environment of Structural Surface

2010 ◽  
Vol 102-104 ◽  
pp. 573-577 ◽  
Author(s):  
Shi Ming Ji ◽  
Bao Li Ma ◽  
Da Peng Tan ◽  
Qiao Ling Yuan
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Flow Field ◽  
Surface Effect ◽  
Computational Method ◽  
Motion Trajectory ◽  
Two Phase ◽  
Leading Role ◽  
Turbulence Flow ◽  
Flow Coupling

As far as the controllability of turbulence flow field surface effect of the soft abrasive flow was concerned, to begin with the analysis of the motion of the particle in the flow field, the paper studied the motion law of particle in the flow field, especially in the boundary layer. Based on the fluid-solid two-phase flow coupling style, it established the single particle dynamics model. Then it established the realizable k-ε model, in the light of the numerical simulation of turbulent flow. With the adoption of the computational method of SIMPLEC, it asked for the velocity and the pressure of fluid in the U-shaped flow passage, the velocity and the motion law of particles with different granularities and velocity, in the boundary layer. Experimentation results tell us that the original velocity plays a leading role in the motion trajectory of particles. The diameter influenced the particles motion trajectory in some degree.

Dynamics and Numerical Modeling of Sandy Desert Morphology Caused by Aeolian Transport of Sand Particles

2011 ◽  
Vol 462-463 ◽  
pp. 1038-1043 ◽  
Author(s):  
Xamxinur Abdikerem ◽  
Mamtimin Gheni ◽  
Abdurahman Ablimit ◽  
A Fang Jin
Keyword(s):  
Numerical Modeling ◽  
Flow Field ◽  
Stream Flow ◽  
Sand Particle ◽  
Threshold Condition ◽  
Sandy Desert ◽  
Aeolian Transport ◽  
Significant Information ◽  
Sand Flow ◽  
Sand Particles

Wind caused the much sediment fluxes leading to both erosion and deposits in the sandy desertification area, and the much kind of beautiful sandy desert morphologies are formed. This is really crucial to the development of the dynamic behaviour of aeolian transport of sand particles. The sand desert morphologies are representing significant information archives for understanding the desertification problem. Dynamics and numerical modeling provides an essential tool for studying the aeolian transport of sand particle and morphology of sand desert such as ripple and dune. In this study, the mathematical models based on the dynamics are analyzed by considering the several keys as saltation, creep, suspension, avalanche and its threshold condition etc. for sand morphology forming processes. Then due to sand flow field real characteristics, the establishing process of stream flow field are analyzed, and the implication relationships as well as the coupling process between uniform stream flow field and the sand flow field are analyzed. Finally, the sand flow field models is discretized, and different kinds of sandy desert morphology are simulated by considering the sand particle size and mass in fixed, semi-fixed and free sand flow field area.

Simulation of Bubble Dynamics in Sub-Cooled Boiling on Fuel Clad in PWRs

2002 ◽  
Author(s):  
Wen Wu ◽  
Barclay G. Jones
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Bubble Dynamics ◽  
Pure Water ◽  
Fluid Velocity ◽  
Safety Margin ◽  
Spherical Model ◽  
Flow Region ◽  
Surface Region ◽  
Bulk Fluid

The crud deposition on nuclear fuel assembly cladding generally increases the resistance to heat transfer, which may result in deterioration of thermal performance, degradation of the fuel cladding, and an axial power shift, i.e. Axial Offset Anomaly (AOA). Crud formation continues to elude prediction. An operational difficulty, of not being able to accurately determine power safety margin, then arises. In some cases, this condition has required decreasing the core power by as much as thirty percent, hence, resulting in considerable loss of revenue for the utility. The specific purpose of this study is to examine bubble dynamics, flow characteristics of the surrounding fluid, and its impact on the formation of the curd. The presence of a bubble on the clad surface affects the flow field around it , particularly in forming a stagnant flow region behind the bubble. The temperature difference between the bubble and the bulk coolant surrounding it causes vaporization at the bubble-clad interface and condensation at its apex. Pure water is thereby moved into the bubble through vaporization resulting in the concentration of solutes in the water at the bubble/wall surface region, which may cause their precipitation on and/or attachment to the clad surface, thereby initiating crud deposition. We investigate analytically and numerically, the growth of a bubble in the boundary layer and the influence of the bubble on the flow. Because of the small bubble size, a spherical model of the bubble is selected for our research. A two-step calculation is applied to this model. In the first step, bubble growth is estimated analytically with omission of the effect of the bulk fluid velocity, a reasonable approximation. In the second step, the flow field around the stationary bubble is obtained through numerical methods. Some parameters in PWR operating condition have been determined approximately e.g. size of the bubble, boundary layer thickness, flow velocity and drag forces on the bubble.

Magnetic bubbles dynamics and heat transfer characteristics under influence of non-uniform magnetic fields

2021 ◽  
pp. 095440622110358
Author(s):  
MM Larimi ◽  
A Ramiar ◽  
H Ramyar ◽  
Hamid Kazemi Moghadam
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Boundary Layer ◽  
External Magnetic Field ◽  
Flow Field ◽  
Thermal Boundary Layer ◽  
Computational Study ◽  
Two Phase ◽  
Navier Stokes Equation ◽  
Vof Model

The computational study of transient immiscible and incompressible two-phase flows is one of the most common and desirable way for investigation of engineering phenomena and physics science. In the previous studies, generally bubbles current have been used as an active method for increasing heat transfer, however, due to existence of hydraulic boundary layers, the bubbles were not able to cross over this layer to thinning the thermal boundary layer and consequently the efficiency of this method was not very considerable. In this study, by considering potential of magnetic field, the effect of co-applying of external non uniform magnetic field and magnetic bubbles in enhancing the heat transfer efficiency in a 3-D tube has been investigated. The computational model consisted of the Navier–Stokes equation for liquid phase and VOF model for interface tracking are carried out by OpenFOAM. The external magnetic field has been considered non-uniform and time dependent. The results predicted that magnetic bubbles and external magnetic field due to their effect on thermal boundary layer increased significantly heat transfer and Nusselt number. Furthermore, results indicated magnetic bubbles can act as an active torbulators in the flow field and can be applied for increasing recirculation and secondary flow in the flow field. The average temperature and magnetic field over times for different cases have been discussed in the results.

scholarly journals Wind Tunnel Test on Windblown Sand Two-Phase Flow Characteristics in Arid Desert Regions

2021 ◽  
Vol 11 (23) ◽  
pp. 11349
Author(s):  
Bin Huang ◽  
Zhengnong Li ◽  
Zhitian Zhang ◽  
Zhefei Zhao ◽  
Bo Gong
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Two Phase ◽  
Windblown Sand ◽  
Sand Flow ◽  
Desert Regions ◽  
Sand Particles ◽  
Arid Desert

Windblown sand two-phase flow characteristics become an essential factor in evaluating the windblown sand load on infrastructures and civil structures. Based on the measured wind characteristics in arid desert regions, windblown sand flow fields with three kinds of sand beds are simulated in the wind tunnel, respectively. The results indicate that the characteristic saltation height of sand particles increases with the wind speed and particle size in the windblown sand flow field. As the sand concentration increases, the wind speed decreases, and the turbulence intensity increases. The concentration, energy, and impact pressure of sand particles increase with increasing wind speed and decrease exponentially with increasing height. At the same wind speed, the concentration, energy, and impact pressure of the coarse sand, fine sand, and mixed sand increases, in turn. Moreover, the variation of kinetic energy with height is similar to that of total energy with height and the proportion of potential energy to total energy is quite small.

Numerical Simulation for Transient Flow of Field of Water Jet Based on Euler Method

2013 ◽  
Vol 694-697 ◽  
pp. 551-554
Author(s):  
Fei Dong ◽  
Shou Chen Xing ◽  
Chen Hai Guo
Keyword(s):  
Numerical Simulation ◽  
Transient Flow ◽  
Fluid Dynamic ◽  
Dynamic Pressure ◽  
Fluid Velocity ◽  
Initial Pressure ◽  
Euler Method ◽  
Water Jet ◽  
Core Area ◽  
Two Phase

It is hard to accurately predict the shape and the characteristic of jet because of the dynamic characteristic of water jet in the atmosphere. The Eulerian model was used to calculate the water jet numerical simulation of two-phase flow. The distribution of the velocity, pressure and the component of the nozzle flow field were obtained under the condition of the initial pressure of nozzle is 100 MPa and the outlet diameter of nozzle is 0.2 mm. The results show that fluid velocity increases rapidly in the nozzle contraction section and appears the isokinetic core area after leaving the nozzle; the fluid dynamic pressure rapid rises in the nozzle contraction section and keeps invariant at the isokinetic core area; the ratio of the contraction flow radius and the nozzle radius is 7:10.

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