Effect of Near Wall Turbulence on the Particle Removal From Bed Deposits in Horizontal Wells

2016 ◽  
Author(s):  
Majid Bizhani ◽  
Ergun Kuru ◽  
Sina Ghaemi
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Reynolds Stress ◽  
Turbulence Intensity ◽  
Experimental Program ◽  
Local Velocity ◽  
Cutting Bed ◽  
Cuttings Bed ◽  
The Impact ◽  
Near Wall

Although solids entrainment and deposition mechanisms have been studied extensively over the years, our understanding of fluids-particle interactions near bed interface is still limited. Progress toward such understanding has been relatively slow because of the difficulties inherent simultaneous measurement of local solids transport and adjacent near-bed fluid flow. With the introduction of non-intrusive measurement techniques such as Particle Image Velocimetry (PIV), it is now possible to determine the instantaneous velocity field and observe particle deposition/resuspension simultaneously under non-uniform flow conditions. An experimental program was conducted to investigate different aspects of turbulent flow of water over the cuttings bed deposited in horizontal annuli. A large-scale horizontal flow loop consisting of 9 m long high quality optic glass pipes (95 mm ID of outer pipe and 38 mm OD of inner pipe) equipped with state of the art PIV system has been used for the experiments. Turbulent flow over cuttings bed experiments were conducted at superficial Reynolds numbers of 9300 and 10800. Natural irregular shaped quartz sands with 3 different mean sieve sizes of 260, 350 and 600 micron were used as solid particles. The proposed work was accomplished through several tasks: i-) conduct experiments to measure the instantaneous local velocity profile during turbulent flow in the horizontal concentric annuli and examine the effect of stationary cutting bed on the local velocity profile, Reynolds stress and turbulence intensity; ii-) investigate the impact of particle size on the near-wall turbulent activities. Results have indicated that existence of a cuttings bed on the lower side of the wellbore dramatically alters the near wall velocity profile comparing to the case with no cuttings bed. Presence of cuttings bed causes the maximum velocity to shift toward the inner pipe. Presence of stationary cutting bed causes a reduction in Reynolds stress, axial and radial turbulence intensity, which in turn, would adversely affect the hole cleaning. Larger cuttings slightly enhanced turbulent stress and radial intensities. However, the increase in these entities as a result of increasing cutting size was far less than the decrease in them as a consequence of presence of stationary cutting bed. Axial turbulence intensity was the same in the core flow away from the cuttings bed for flow with and without a cuttings bed. However, the peak of axial intensities is shown to be less for flow near the cuttings bed.

Effect of Sand Bed Deposits on the Characteristics of Turbulent Flow of Water in Horizontal Annuli

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Turbulent Flow ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Velocity Profiles ◽  
Experimental Program ◽  
Critical Flow ◽  
Local Velocity ◽  
Flow Rates ◽  
Critical Flow Rate ◽  
Horizontal Annuli

An experimental program was conducted to investigate turbulent flow of water over the stationary sand bed deposited in horizontal annuli. A large-scale horizontal flow loop equipped with the state-of-the-art particle image velocimetry (PIV) system has been used for the experiments. Experiments were conducted to measure the instantaneous local velocity profiles during turbulent flow and examine the impact of the presence of a stationary sand bed deposits on the local velocity profiles, Reynolds shear stresses and turbulence intensities. Results have shown that the existence of a stationary sand bed causes the volumetric flow to be diverted away from the lower annular gap. Increasing the sand bed height causes further reduction of the volumetric flow rate in the lower annulus. Velocity profiles near the surface of the bed deposits showed a downward shift from the universal law in wall units indicating that the flow is hydraulically rough near the sand bed. The equivalent roughness height varied with flow rates. At flow rates less than the critical flow rate, the Reynolds stress profile near the bed interface had slightly higher peak values than that of the case with no sand bed. At the critical flow rate, however, the peak Reynolds stress values for the flow over the sand bed was lower than that of the case with no bed. This behavior is attributed to the bed load transport of sand particles at the critical flow rate.

Simplified theory of the near-wall turbulent layer of Newtonian and drag-reducing fluids

1982 ◽  
Vol 119 ◽  
pp. 423-441 ◽  
Author(s):  
M. A. Goldshtik ◽  
V. V. Zametalin ◽  
V. N. Shtern
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Outer Boundary ◽  
Viscous Sublayer ◽  
Viscous Layer ◽  
Mean Velocity ◽  
Turbulent Layer ◽  
The Mean ◽  
Near Wall

We propose a simplified theory of a viscous layer in near-wall turbulent flow that determines the mean-velocity profile and integral characteristics of velocity fluctuations. The theory is based on the concepts resulting from the experimental data implying a relatively simple almost-ordered structure of fluctuations in close proximity to the wall. On the basis of data on the greatest contribution to transfer processes made by the part of the spectrum associated with the main size of the observed structures, the turbulent fluctuations are simulated by a three-dimensional running wave whose parameters are found from the problem solution. Mathematically the problem reduces to the solution of linearized Navier-Stokes equations. The no-slip condition is satisfied on the wall, whereas on the outer boundary of a viscous layer the conditions of smooth conjunction with the asymptotic shape of velocity and fluctuation-energy profiles resulting from the dimensional analysis are satisfied. The formulation of the problem is completed by the requirement of maximum curvature of the mean-velocity profile on the outer boundary applied from stability considerations.The solution of the problem does not require any quantitative empirical data, although the conditions of conjunction were formulated according to the well-known concepts obtained experimentally. As a result, the near-wall law for the averaged velocity has been calculated theoretically and is in good agreement with experiment, and the characteristic scales for fluctuations have also been determined. The developed theory is applied to turbulent-flow calculations in Maxwell and Oldroyd media. The elastic properties of fluids are shown to lead to near-wall region reconstruction and its associated drag reduction, as is the case in turbulent flows of dilute polymer solutions. This theory accounts for several features typical of the Toms effect, such as the threshold character of the effect and the decrease in the normal fluctuating velocity. The analysis of the near-wall Oldroyd fluid flow permits us to elucidate several new aspects of the drag-reduction effect. It has been established that the Toms effect does not always result in thickening of the viscous sublayer; on the contrary, the most intense drag reduction takes place without thickening in the viscous sublayer.

scholarly journals Assessing Spacing Impact on Coherent Features in a Wind Turbine Array Boundary Layer

2017 ◽  
Author(s):  
Naseem Ali ◽  
Nicholas Hamilton ◽  
Raul Cal
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Wind Turbine ◽  
Reynolds Stress ◽  
Flow Structure ◽  
Energy Content ◽  
Turbulence Kinetic Energy ◽  
Flow Structures ◽  
Spanwise Direction ◽  
The Impact

Abstract. As wind farms become larger, the spacing between turbines becomes a significant design element that imposes serious economic constraints. Effects of turbine spacing on the power produced and flow structure are crucial for future development of wind energy. To investigate the turbulent flow structures in a 4 × 3 Cartesian wind turbine array, a wind tunnel experiment was carried out parameterizing the streamwise and spanwise wind turbine spacing. Four cases were chosen spacing turbines by 6 diameters (D) or 3D in the streamwise, and 3D or 1.5D in the spanwise direction. Data were obtained experimentally using stereo particle-image velocimetry. Mean streamwise velocity showed maximum values upstream of the turbine with the spacing of 6D and 3D, in the streamwise and spanwise direction, respectively. Fixing the spanwise turbine spacing to 3D, variations in the streamwise spacing influence the turbulent flow structure and the power available to following wind turbines. Quantitative comparisons were made through spatial averaging, shifting measurement data and interpolating to account for the full range between devices to obtain data independent of array spacing. The largest averaged Reynolds stress is seen in cases with spacing of 3D and 3D, in the streamwise and spanwise direction, respectively. Snapshot proper orthogonal decomposition was employed to identify the flow structures based on the turbulence kinetic energy content. The maximum turbulence kinetic energy content in the first POD mode compared with other cases is seen for turbine spacing of 6D × 1.5D. The flow upstream of each wind turbine converges faster than the flow downstream according to accumulation of turbulence kinetic energy by POD modes, regardless of spacing. The streamwise-averaged profile of the Reynolds stress is reconstructed using a specific number of modes for each case; the case of 6D × 1.5D spacing shows the fastest reconstruction. Intermediate modes are also used to reconstruct the averaged profile and show that the intermediate scales are responsible for features seen in the original profile. The variation in streamwise and spanwis spacing leads to changing the background structure of the turbulence, where the color map based on barycentric map and anisotropy stress tensor provides a new perspective on the nature of the perturbations within the wind turbine array. The impact of the streamwise and spanwise spacings on power produced is quantified, where the maximum production corresponds with the case of greatest turbine spacing.

scholarly journals Assessing spacing impact on coherent features in a wind turbine array boundary layer

2018 ◽  
Vol 3 (1) ◽  
pp. 43-56 ◽  
Author(s):  
Naseem Ali ◽  
Nicholas Hamilton ◽  
Dominic DeLucia ◽  
Raúl Bayoán Cal
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Flow ◽  
Wind Turbine ◽  
Reynolds Stress ◽  
Energy Content ◽  
Turbulence Kinetic Energy ◽  
Flow Structures ◽  
Spanwise Direction ◽  
The Impact

Abstract. As wind farms become larger, the spacing between turbines becomes a significant design consideration that can impose serious economic constraints. To investigate the turbulent flow structures in a 4 × 3 Cartesian wind turbine array boundary layer (WTABL), a wind tunnel experiment was carried out parameterizing the streamwise and spanwise wind turbine spacing. Four cases are chosen spacing turbines by 6 or 3D in the streamwise direction, and 3 or 1.5D in the spanwise direction, where D = 12 cm is the rotor diameter. Data are obtained experimentally using stereo particle image velocimetry. Mean streamwise velocity showed maximum values upstream of the turbine with the spacing of 6 and 3D in the streamwise and spanwise direction, respectively. Fixing the spanwise turbine spacing to 3D, variations in the streamwise spacing influence the turbulent flow structure and the power available to following wind turbines. Quantitative comparisons are made through spatial averaging, shifting measurement data and interpolating to account for the full range between devices to obtain data independent of array spacing. The largest averaged Reynolds stress is seen in cases with spacing of 3D × 3D. Snapshot proper orthogonal decomposition (POD) was employed to identify the flow structures based on the turbulence kinetic energy content. The maximum turbulence kinetic energy content in the first POD mode is seen for turbine spacing of 6D × 1.5D. The flow upstream of each wind turbine converges faster than the flow downstream according to accumulation of turbulence kinetic energy by POD modes, regardless of spacing. The streamwise-averaged profile of the Reynolds stress is reconstructed using a specific number of modes for each case; the case of 6D × 1.5D spacing shows the fastest reconstruction to compare the rate of reconstruction of statistical profiles. Intermediate modes are also used to reconstruct the averaged profile and show that the intermediate scales are responsible for features seen in the original profile. The variation in streamwise and spanwise spacing leads to changes in the background structure of the turbulence, where the color map based on barycentric map and Reynolds stress anisotropy tensor provides an alternate perspective on the nature of the perturbations within the wind turbine array. The impact of the streamwise and spanwise spacings on power produced is quantified, where the maximum production corresponds with the case of greatest turbine spacing.

Influence of Flue Gas Turbulence Intensity on the Heat and Mass Transfer and Pressure Drop Inside a TMC Based Heat Exchanger

2021 ◽  
Author(s):  
Saja Al-rifai ◽  
Cheng-Xian Lin
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Heat And Mass Transfer ◽  
Turbulence Intensity ◽  
Flue Gas ◽  
Condensation Rate ◽  
The Impact

Abstract In this study, a numerical analysis of turbulent flow heat and mass transfer in the cross-flow transport membrane condenser (TMC) based heat exchange was carried out. The heat exchanger under investigation was designed to recover both sensible and latent heat due to transport of heat and mass through a nanoporous ceramic membrane in the bundle of tubes of the heat exchanger. The shear stress transport SST k-ω turbulence model was used to model the turbulent flow of the flue gas mixture. The condensation rate of the water vapor from the flue gas were calculated using a mixed condensation model. The mixed model was based on the capillary condensation and wall condensation in the membrane tube. The numerical study was focused on the investigation of the impact of the turbulence intensity of the flue gas at various inlet conditions, such as Reynolds numbers and temperatures, on the heat and mass transfer and pressure drop characteristics. The numerical results were validated against the experimental results reported in the literature. Different tube diameters were used in the simulation, with the Reynolds number varied from 3000 to 10000. The results showed that an increase in turbulence intensity led to a significant increase in the turbulent kinetic energy, condensation rate, average convective Nusselt number and change on the pressure drop in the heat exchanger. The effects of inlet flow Reynolds number and tube diameter on the heat and mass transfer were also presented and discussed.

A CFD Simulation of Near Wall Turbulent Flow in Concentric Annulus

2013 ◽  
Author(s):  
Aziz Rahman ◽  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Experimental Data ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Water Flow ◽  
Simulation Study ◽  
Cfd Simulation ◽  
Concentric Annulus ◽  
Sst Model ◽  
Cfd Analyses ◽  
Near Wall

A CFD simulation study was conducted to analyse the near wall turbulence characteristics of water flow through concentric annulus. The continuity and momentum equations were solved by using a commercial CFD package (CFX 14) with the Shear-Stress-Transport (SST) model option. The simulation results were compared to the experimental data obtained by using high resolution Particle Image Velocimetry (PIV) analyses of water flow in a horizontal concentric annulus. A fully developed turbulent flow of water through a horizontal flow loop (ID = 9.5 cm) with concentric annular geometry (inner to outer pipe radius ratio = 0.4) was used for comparison purpose. Reynolds number ranged from 17,500 to 68,500. Annular velocity profile obtained from simulation study showed good agreement with the experimental data. Near wall velocity profile obtained from CFD simulation followed the universal wall law (u+ = y+) up to y+ = 11. CFD analyses using the SST model resulted a good number of velocity data up to y+ = 11, which is normally a very difficult task to achieve experimentally. The CFD analyses using SST model is computationally inexpensive and therefore, can be conveniently used for investigating the near wall turbulent characteristics of flow in concentric annulus.

Analysis of Turbulent Flow Around Horizontal Axis Wind Turbines Using Algebraic Stress Model

2015 ◽  
Author(s):  
Saman Beyhaghi ◽  
Ryoichi S. Amano
Keyword(s):  
Turbulent Flow ◽  
Wind Turbine ◽  
Reynolds Stress ◽  
Wind Turbines ◽  
Cost Effective ◽  
Horizontal Axis ◽  
Stress Model ◽  
Reynolds Stresses ◽  
Algebraic Stress Model ◽  
Near Wall

Due to the problems associated with increase of greenhouse gases, and the limited supply of fossil fuels, switching to clean and renewable sources of energy seems necessary. Wind energy is a very suitable form of renewable energy which can be a good choice for those areas around the world with sufficient amount of wind annually. However, in order for the commercial wind turbines to be cost-effective, they need to operate at very high elevations, and therefore, blades with the length as high as 60–70 m are common. Because of the high manufacturing and transportation costs of the wind turbine components, it is necessary to evaluate and predict the performance of the turbine prior to shipping it to the installation site. Computational Fluid Dynamics (CFD) has proven to be a simple, cheap and yet relatively accurate tool for prediction of wind turbine performance, where suitability of different designs can be evaluated at a low cost. Total lift and drag forces can be calculated, from which one can estimate the torque, and ultimately the output power. Reynolds Stress Model (RSM) is a well-known Reynolds Averaged Navier-Stokes (RANS) turbulence model, which is typically more accurate than eddy viscosity models, but it comes with higher computational cost. In the present work, turbulent flow of air around a horizontal axis wind turbine blade is modeled computationally by using a modified version of RSM, known as Algebraic Stress Model (ASM) for the near-blade region. Because of the periodicity nature of the flow domain, only one of three blades is modeled by applying the periodic conditions on the sides of a 120 degree sector of the domain. While the flow is solved in the bulk fluid using the k-epsilon model, in order to better capture the near-wall effects and to make the computations cost effective, it is proposed to apply ASM only in the locations very close to the blade surface. A number of reasonable assumptions are made in ASM in order to convert the transport differential equations of the Reynolds stresses into an algebraic form. The highly coupled system of non-linear equations is then solved concurrently for six Reynolds stress components. Turbulent kinetic energy, turbulent dissipation rate, and mean velocity gradients are calculated from the k-epsilon model and used as initial values and iterated through the ASM computations. To the best of our knowledge, this is the first time that ASM is used for analysis of Reynolds stress for flow around rotating wind turbines blades. Reynolds stresses are obtained at several locations (heights) along the blade, and at different radial distances from the blade. Different variations of implicit and explicit ASM are examined and compared in terms of accuracy. Results indicate that the implicit ASM method using the full form of pressure-strain term tends to show predictions that are closer to the predictions of the fully-resolved RSM simulation, as compared to the other ASM models examined. Therefore, there seems to be a good potential for reducing computational costs for determination of near wall Reynolds stresses and ultimately calculating torque and power generated from wind turbines without sacrificing the accuracy.

scholarly journals Mass Transport and Turbulent Statistics within Two Branching Coral Colonies

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 153
Author(s):  
Md Monir Hossain ◽  
Anne E. Staples
Keyword(s):  
Mass Transport ◽  
Turbulent Flow ◽  
Reynolds Stress ◽  
Transport Processes ◽  
Transport Mechanisms ◽  
Local Flow ◽  
Turbulent Statistics ◽  
The Mean ◽  
Mass Transport Mechanisms ◽  
The Impact

Large eddy simulations were performed to characterize the flow and mass transport mechanisms in the interior of two Pocillopora coral colonies with different geometries, one with a relatively loosely branched morphology (P. eydouxi), and the other with a relatively densely branched structure (P. meandrina). Detailed velocity vector and streamline fields were obtained inside both corals for the same unidirectional oncoming flow, and significant differences were found between their flow profiles and mass transport mechanisms. For the densely branched P. meandrina colony, a significant number of vortices were shed from individual branches, which passively stirred the water column and enhanced the mass transport rate inside the colony. In contrast, vortices were mostly absent within the more loosely branched P. eydouxi colony. To further understand the impact of the branch density on internal mass transport processes, the non-dimensional Stanton number for mass transfer, St, was calculated based on the local flow time scale and compared between the colonies. The results showed up to a 219% increase in St when the mean vortex diameter was used to calculate St, compared to calculations based on the mean branch diameter. Turbulent flow statistics, including the fluctuating velocity components, the mean Reynolds stress, and the variance of the velocity components were calculated and compared along the height of the flow domain. The comparison of turbulent flow statistics showed similar Reynolds stress profiles for both corals, but higher velocity variations, in the interior of the densely branched coral, P. meandrina.

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