Maximum Turbulent Kinetic Energy Research Articles

Do fishways stress fish? Assessment of physiological and hydraulic parameters of rainbow trout navigating a novel W-weir fishway

Experiments were performed in a novel pool & weir fishway to study the relationship between hydrodynamic and physiological parameters using rainbow trout (Oncorhynchus mykiss; mean TL = 15 cm). Fish were tested randomly using three fishway slopes (4, 7 and 10%) and three spacing ratios of W shaped weirs. Effect on fish hematology, immunology and stress were examined. Results showed that changing fishway hydraulic conditions altered fish stress levels. Increasing fishway slope and decreasing weir spacing, resulted in increased number of red blood cells and hematocrit, and decreased white blood cell count and serum lysosomes. In addition, levels of the most important stress indicator, cortisol, were elevated significantly compared to the control group, as slope, and consequently turbulence levels increased. Results showed that maximum turbulent kinetic energy (TKE) for a 10% fishway slope was increased to 0.22 m2/s2 while for a 4% slope and larger weir spacing was reduced to 0.05 m2/s2 which is the best condition for fish to rest in the pools created between the weirs. Observations on turbulence metrics showed that a weir spacing ratio of 6 offered the lowest gradients of energy changes. Furthermore, increasing the spacing ratio from 2 to 6 reduced cortisol levels and generally improved the physiological status of fish in the fishway. Considering turbulence levels at different depths of flow, the study concluded that physiological conditions for the passage of rainbow trout were best for a spacing ratio of 6 and a fishway slope of 4%. The evaluation of physiological metrics proved to be a vital and reliable process to integrate with hydrodynamics so fishway designs may be optimized to avoid stressing fish, and to enhance survival opportunities for migrating populations.

Investigation of flow characteristics for triangular grooved shape cylinder at different heights in shallow water

This study is an investigation and comparison of the flow characteristic around triangular grooved and bare cylinders, positioned horizontally in shallow water using Particle Image Velocimetry (PIV). Throughout the experiment, Reynolds number, Froude number and water height have been selected as 5000, 0.27 and 90 mm, respectively. To observe the effect of height (h) on the flow structure, cylinder is positioned at h: 0 mm, 15 mm, 22.5 mm, 30 mm, 37.5 mm, 45 mm, 52.5 mm and 60 mm. Moreover, grooved angle (a) has been changed from 0°, 80°, 85°, 90° and 95° in shallow water to investigate the effect of grooved angle. The results show that the vortex forms vary according to the groove angle. It is seen that the vortex, the cylinders especially positioned at h: 0 mm and h: 60 mm, are affected owing to the surface and bottom effect. Furthermore, the largest Reynolds stress is observed at the h: 37.5 mm while the largest wake region is observed at the h: 52.5 mm. Also, the maximum Drag Coefficient (Cd) and Turbulence Kinetic Energy (TKE) are observed at h: 0 mm, a: 90° for grooved cylinder and at h: 37.5 mm for bare cylinder, respectively.

Modelling of flow pattern in an open channel with sidewall obstruction

To predict flow pattern of shallow obstructed open channel flows, laboratory experiments of flow around a vertical emergent sidewall abutment (lateral constriction) in an open channel flow is simulated numerically and results of water surface and vertical profile of velocity are compared with the numerical results. The turbulence kinetic energy at the separation zone and bed shear stresses are also investigated. A computational fluid dynamic (CFD) numerical tool and volume of fluid (VOF) were used to predict water surface profiles. Results showed a very good agreement between the numerical and the experimental results of the water surface profiles. The numerical findings highlighted an increase in the velocity around the structure of two times the average flow velocity. The maximum pressure was observed in front of the constriction increases with increasing discharges. The vertical velocity profiles upstream the sidewall abutment at the three selected locations showed reasonable results. The maximum turbulence kinetic energy is shown at the zone of separation when the flow passes around the nose with high velocity. In this research, numerically it was found that the estimated bed shear stresses are 2-3 times the mean bed-shear stress of incoming flow. While, previous researchers finding showed a maximum value of bed shear stress near the leading edge 3.63 to 5 times the bed shear stress of the incoming flow. Because of the wide rang variation in calculating bed shear stresses by the previous researchers, so our research aims to calculate it using CFD and compare it with others. Also, dynamics of the flow around the obstacle was considered in this research under uniform flow conditions for an aspect ratio ranged 5 to 10.

Investigation of Flow Pattern around Rectangular and Oblong Piers with collar Located in a 180o Sharp Bend

Flow in river bends is associated with generation of secondary flows that leads to a rather complicated flow pattern around bridge piers located in the bend. In this study, the flow patterns around rectangular and oblong piers models with collar located at the 90o angle of a 180-degree sharp bend in an experimental plume were investigated. The 3D flow velocity data were collected using a Vectrino velocimeter. The experimental results indicated that the presence of the rectangular pier caused more intense deviation of the streamlines towards the outer bank of the bend. Furthermore, installation of the oblong pier, the maximum secondary flow power and angular velocity were decreased, respectively, by 35% and 45% in comparison with the installation of the rectangular pier. In addition, it was found that the maximum turbulence kinetic energy around the two piers was not significantly different, but by installing the rectangular pier, a region with high values of turbulence kinetic energy is formed at 90° near the inner bank. Also, installation of oblong pier reduces the values of shear stress in comparison with the use of the rectangular pier.

Study of Unsteady Flow Through and Around an Array of Isolated Square Cylinders

Abstract Flow past a porous square cylinder, which is constituted by an array of small square cylinders, was studied by simplified and highly stable lattice Boltzmann method (LBM) at Re = 4000. The effects of solid volume fractions (SVF) on the flow structure and important aerodynamic parameters were investigated and the internal fluid was described by phase-averaged method and its interaction with the near region. Several energy-contained Strouhal numbers come up in cylinder arrays, and mass flux through arrays is calculated to estimate the effects of blocking. The average total force on the array is found to decrease monotonically with decreasing SVF, and it has a dramatic drop as SVF decreasing from 0.062 to 0.036. The mass flux of array for SVF = 0.062 is smaller than that of 0.073 due to the stagger arrangement of isolated cylinders. The underlying Reynolds stresses reveal the increase in mean wake length as SVF decreases, and it behaves like the solid one for SVF = 0.132. Comparing with the other SVFs, the shear layer region at SVF = 0.132 indicates a significant decrease of curvature and a linear increase of growth rate, but a nonlinear growth rate for the other SVFs can be observed. The local maximum turbulent kinetic energy (TKE) and vorticity in shear layer region reveal the variation during the initial stages following separation. Moreover, detailed investigations of instantaneous wake dynamics provide an assistance to understand the flow physics of cylinder arrays for different SVF.

Three-dimensional numerical simulation of local scour around circular side-by-side bridge piers with ice cover

Local scour around piers is one of the primary causes of collapse of bridges that cross rivers. The most severe scouring occurs in cold regions where ice cover significantly changes the velocity profile. Having an accurate estimation of the maximum scour depth around bridge piers, especially in cold regions, is necessary for a safer design of piers. In this study, 3D numerical models are compared to laboratory experiments to examine the process of local scour around bridge piers with and without smooth and rough ice cover. By using the equation of Meyer-Peter and Müller, the sediment transport model is validated to approximate the transport of the sediment particles. Numerical results showed good agreements with experimental observations where the maximum scour depth and turbulent kinetic energy around bridge piers were the highest under rough ice cover conditions.

Impeller shape-optimization of stirred-tank reactor: CFD and fluid structure interaction analyses

Mixing is an important operation in the chemical industry. The present numerical study, validated by experimental data, offers a computational framework for minimizing the stirred-tank reactor power consumption and the impeller equivalent stress. The flow pattern, turbulence parameters, and power consumption of the three types of impellers, named as 6-blade Rushton turbine and U-shape and V-shape impeller designs, are numerically studied using the Computational Fluid Dynamic (CFD) analysis. The interaction between the fluid and the solid is then studied through a two-way Fluid Structural/Solid Interaction (FSI) analysis. Multi-objective Genetic Algorithm (MOGA) is used along with both Direct Optimization (DO) and Response Surface Optimization (RSO) to optimize the blade’s geometrical parameters, including blade thickness (Tb), disk thickness (TD), and vertical angle of the blade (θ). The variation between experimental and numerical results, in terms of power consumption, is around 5%. The computational results show that the power number (Np) can decrease, respectively by 21% and 48%, for the V- and U-shape impellers compared to the 6-blade Rushton turbine. The maximum turbulent kinetic energy and the maximum dissipation rate of the turbulent kinetic energy of the U-shape (k = 0.065 m2/s2, ε = 65.14 m2/s3) are more than V-shape impeller (k = 0.044 m2/s2, ε = 25.16 m2/s3). The FSI results also show that the lowest von Mises stress occurs in the V-shape impeller.

Modeling and analysis of highway emission dispersion due to noise barrier and automobile wake effects

Highway automobile emissions is an important environmental issue and can be complex due to the influences of multiple factors such as noise barrier configurations, vehicle induced wake flows, and traffic flow conditions. To better understand this phenomenon, a three-dimensional computational fluid dynamics (CFD) model has been developed and implemented to simulate the automobile emissions dispersion under various conditions. The model was first validated by comparing simulation results of velocity and emission concentration with data from a wind tunnel experiment in the literature. Furthermore, simulation and analysis revealed that with the existence of noise barriers, the automobile wake region was enlarged, the flow recirculation zone was enhanced, and the emission concentration level was increased. In addition, vehicle body geometry effects were simulated and analyzed. Results showed that the maximum turbulent kinetic energy can be observed on the upper and lower surfaces of a vehicle due to the shear layer and flow separation. For different vehicle body geometry with slant angle effects, turbulent kinetic energy and the concentration of emission around the vehicles were reduced. Traffic speed, another major factor in highway automobile emissions in general, resulted in more emissions remaining on the highway in congestion cases. Simulation results from this research will help to find possible solutions to solve this environmental issue by obtaining a better understanding of highway automobile emissions through the analyzation of the effects of noise barrier configurations, vehicle induced wake flows, and traffic flow conditions.

Numerical Investigation of Vertical Crossflow Jets with Various Orifice Shapes Discharged in Rectangular Open Channel

Vertical jet in flowing water is a common phenomenon in daily life. To study the flow and turbulent characteristics of different jet orifice shapes and under different velocity ratios, the realizable k-ε turbulent model was adopted to analyze the three-dimensional (3D) flow, turbulence, and vortex characteristics using circular, square, and rectangular jet orifices and velocity ratios of 2, 5, 10, and 15. The following conclusions were drawn: The flow trajectory of the vertical jet in the channel exhibits remarkable 3D characteristics, and the jet orifice and velocity ratio have a significant influence on the flow characteristics of the channel. The heights at which the spiral deflection and maximum turbulent kinetic energy (TKE) occur for the circular jet are the smallest, while those for square jets are the largest. As the shape of the jet orifice changes from a circle to a square and then to a rectangle, the shape formed by the plane of the kidney vortices and the region above it gradually changes from a circle to a pentagon. With the increase in the velocity ratio, the 3D characteristics, maximum TKE, and kidney vortex coverage of the flow all gradually increase.

Modelling Stilling Basins for Sewage Networks

Concrete elements play an effective role in stilling basin design in terms of enhancing the dissipation of energy to prevent immoderate scouring of downstream structures. Proper appurtenances, such as wedge-shaped splitter blocks, baffle walls, inverted t-sections, rectangular walls, inverted L sections, and impact walls, are thus utilised with circular pipe outlets to create stilling basins that are shorter yet more effective, and thus more economical. This research was based on numerical analysis of stilling basins using FLOW-3D software; the resulting Froude numbers were compared with the Froude number of a case study, a stilling basin manhole created by the Karbala Government. This research thus examined the influence of Froude number, the arrangement and location of dissipators, and the height of the pipe inlet under different hydraulic condition in order to better simulate stilling basin models. The turbulent energy dissipation was found to vary from 16% to 85%. The results from the models showed that L-sections offered maximum turbulent energy dissipation (ΔE/E1), while the rectangular wall shape gave minimum turbulent energy dissipation (ΔE/E1). It was also observed that the maximum turbulent kinetic energy almost always occurred in the initial sections, with flow becoming generally less turbulent at the end sections. Thus, at the end of all stilling basins, the turbulent kinetic energy dissipation and turbulent kinetic energy profiles became more uniform. The proposed numerical simulation using FLOW-3D was shown to be a reliable tool for predicting and discussing the turbulent energy dissipation in stilling basins. Further conclusions included the fact that the maximum turbulent energy dissipation (ΔE/E1) increases as values of Fr increase. The results of this research could thus help hydraulic designers to consider their selections for the optimum design of stilling basins more carefully.

Numerical Simulation of the Flow Field and Pollutant Dispersion around a Hill under Different Thermal Stratifications

AbstractThis paper applied a commercial computational fluid dynamics code, STAR-CD, with the renormalization group k–ε turbulence model to simulate the flow and dispersion of contaminants released from a source on the windward side of a hill under different thermal stratifications. In the wake region, the influence of atmospheric stratification on the flow field is inconspicuous under neutral and unstable conditions because of the effect of mechanical disturbance. However, this influence becomes slightly conspicuous under stable conditions. When atmospheric stratification is stable, in the range of z/H < 1.0 (where z is height above the surface and H is height of the hill), the velocity deficits are smaller than those under neutral and unstable conditions. The maximum turbulence kinetic energy (TKE) appears in the wake regions, and the variation in TKE is significantly lower than that under neutral and unstable conditions. When atmospheric stratification is unstable, the vertical and horizontal spread of the plume is slightly greater than that under neutral and stable conditions and the maximum concentration is less than that under neutral conditions. When the Froude number is large (~11; Brunt–Väisälä frequency = 0.52), atmospheric stratification is slightly stable, the structure of flow around the hill is generally similar to that under neutral conditions, and the high-concentration regions are large on the windward side of the hill. Smaller high-concentration regions just appear on the windward side of the hill under unstable conditions. The pollutant concentrations in the wake region of the hill increase as a result of the effect of thermal stability, and the vertical spreading range of the plume along the downwind axis (x axis) is larger than that under neutral and stable conditions.

An experimental investigation of flow resistance and turbulent flow in brush fish pass

The flow and turbulence structure of a brush fish pass was investigated in a 1:2 physical model for Reynolds numbers of 5·46 × 104–1·78 × 105 and Froude numbers of 0·18–0·72. Experiments were performed with three different bed slopes (2, 4, and 6%) and four different areal bristle densities. For each bed slope and bristle density, data were collected for six different relative submergences of emergent flexible bristles. Bristle density and channel bed slope were found to play a crucial role in the experiments. From dimensional analysis and physical model measurements and calculations, the friction factor was derived for the brush fish pass. The main findings can be summarised as follows; (a) flow resistance was found to be a function of the Cauchy number of the bristles, the channel bed slope and bristle density; (b) the channel bed slope is a main parameter that controls the maximum velocity and turbulent kinetic energy (TKE) magnitudes; and (c) the spatially averaged TKE seems to be considerably lower for the same dissipated power in a brush fish pass compared with other conventional fish passes (vertical slot and natural types). Hydraulic design recommendations are given to avoid a tumbling flow regime and drag coefficient scale effects.

Flow and heat transfer of nanofluid in a channel partially filled with porous media considering turbulence effect in pores

The flow and heat transfer of Al2O3–water nanofluid in a channel partially filled with porous media is investigated numerically. The turbulence effect in the porous media is taken under consideration in this article. A simple case is simulated first to evaluate the accuracy of the results in comparison with the available data. The turbulent kinetic energy profile is investigated at a flow cross section. The results show that the maximum turbulent kinetic energy occurs in the clear fluid region in the vicinity of the porous media region. The turbulent kinetic energy is a decreasing function of the porosity of the porous medium. The effect of porosity on the variation of turbulent kinetic energy decreases with the increase in the porosity of the porous medium. The turbulent kinetic energy in clear fluid and porous media regions decreases with the increase in nanofluid concentration from 0.01 to 0.03, and it increases with the increase in nanofluid concentration from 0.03 to 0.05. The temperature of the nanofluid increases with the increase in the nanofluid concentration and decrease in the porosity of porous media. It is shown that for this case, with the increase in nanofluid concentration and porosity of porous media, the skin friction coefficient increases and the Nusselt number decreases.

Impact of Vegetation Density on the Wake Structure

Research of interactions between in-channel vegetation and flow structure is important for the restoration of aquatic ecosystems. This study aims to investigate the impact of the vegetation patch density on the wake structure. We used uniform fiberglass circular cylinders to simulate the non-submerged rigid plant community. In addition, a wide range of vegetation patch densities was considered and a 3D acoustic Doppler velocimeter (ADV) was used to measure local flow velocities. High-density vegetation patches correlated with a high maximum turbulent kinetic energy and a double-peak phenomenon for the lateral distribution. In conclusion, differences between Reynolds shear stresses near the bed surface upstream and downstream of vegetation patches correlate with the vegetation density.

Effects of Emergent Vegetation Patterns on Flow Velocity, Turbulence, and Erosion Around River Banks

The effects of two different emergent vegetation patterns on the flow velocity and turbulent kinetic energy (TKE) along the vegetated banks are experimentally investigated with natural reed stems. The results reveal that vegetation patterns can significantly alter the distributions of flow velocity and TKE. At locations for the maximum TKE, closed concentric circles named recirculation cells are observed. The location for the maximum TKE which may induce potential soil erosion for partly vegetated pattern moves forward 1 m in comparison with the vegetated pattern. An empirical function is found to describe the variations of TKE along the flow direction. Gentler distributed flow velocity and lower TKE at the rear part of the vegetation section for partly vegetated pattern suggest that vegetation pattern is an important factor for aquatic vegetation recovery in rivers. The findings of the research may provide some guidance for the engineering practices of river ecological restoration with aquatic vegetation.

The use of computational fluid dynamics to predict the turbulent dissipation rate and droplet size in a stirred autoclave

The prediction of droplet sizes in emulsions is important for fields ranging from the chemical process industry to emergency planning in the event of an underwater oil release. Typically scale models have needed to be built and the results scaled up, but as computational resources have grown and turbulence models have matured it has become possible to use computational fluid dynamics (CFD) to simulate the behaviour of the fluid/s. While direct simulation of multiphase breakup at high Reynolds number is currently computationally impractical, this paper looks into the use of CFD along with a correlation function based on maximum turbulent kinetic energy dissipation rate to predict the Sauter mean diameter of droplets in a 1 in. baffle-and-vane type autoclave. The results show that using a RNG-k∊ turbulence model with a simplified 2D geometry gave droplet sizes within 26.2 μm of the Sauter mean diameter observed in experiments with no additional tuning of parameters. Correlating pipe and autoclave flows through the Reynolds number and the turbulent kinetic energy dissipation rate was also investigated. Using the traditional definitions of the Reynolds numbers the correlation is poor, the coefficient of determination of the linear fit to the log-log data is 0.64. The first modification replaced the diameter of the blade as characteristic length with the tip swept circumference which increased the coefficient of determination to 0.960. A further modification using data obtained from the turbulent fields of the simulation showed a significant improvement with the coefficient of determination increasing to 0.988.

A Hooked-Collar for Bridge Piers Protection: Flow Fields and Scour

A new type of collar, the hooked-collar, was studied through experiments and numerical methods. Tests were conducted using a hooked collar of a width of 1.25b and a height of 0.25b, where b is the bridge-pier width. The hooked-collar efficiency was evaluated by testing different hooked-collar placements within the bridge-pier, which were compared to the bridge-pier without any collar. A double hooked-collar configuration, one placed at the bed level and the other buried 0.25b, was the most efficient at reducing the scour hole. In other cases, a hooked-collar positioned 0.25b above the bed slightly reduced the scour hole and had similar scour patterns when compared to the pier without the hooked-collar. The flow fields along the vertical symmetrical plane in the experiments are also presented. Laboratory experiments and numerical tests show that maximal downflow is highly reduced along with a corresponding decrease in horseshoe vortex strength for the experiments with the hooked-collar, compared to cases without the hooked-collar. The flow fields reveal that the maximum turbulent kinetic energy decreases with the installation of the hooked-collar.

수축부 길이 변화에 따른 풍동 내부유동장 특성에 대한 수치해석

The steady-state, incompressible and three-dimensional numerical analysis was carried out to investigate the internal flow field characteristics of wind tunnel according to the change of contraction length. This study used a realizable k-ε turbulence model. As a result, regardless of the contraction lengths, the minimum value of the axial mean velocity component at the entrance of the plenum chamber is increased through the contraction and has the maximum value in the test section. When the flow passes through the inner space of the analytical models, the average pressure and axial force due to the surface pressure acting at the inlet of the plenum chamber is the smallest at the contraction length of 1,000 mm, but the axial force due to the surface stress increases as the contraction length increases. The maximum turbulent kinetic energy in the test section decreases as the contraction length increases. Comprehensively, it can be concluded that the contraction length of 1,000 mm at the contraction area ratio of 9:1 is the best choice for wind tunnel selection with superior performance.

High Reynolds number incompressible turbulent flow inside a lid-driven cavity with multiple aspect ratios

The numerical simulation of incompressible turbulent flow at Re = 11 800 (equivalent Reynolds number Rem = 10 030) inside lid-driven cavities with varying spanwise aspect ratio and depthwise aspect ratio (DAR) has been carried out using the dynamic Smagorinsky model. A better comparison of central line averaged velocities and second order turbulent properties is obtained with the existing experimental result of Prasad and Koseff [“Reynolds number and end-wall effects on a lid-driven cavity flow,” Phys. Fluids A 1, 208–218 (1989)] than with the one provided by Leriche and Gavrilakis [“Direct numerical simulation of the flow in a lid-driven cubical cavity,” Phys. Fluids 12, 1363–1376 (2000)]. It is noticed that the size of the downstream secondary vortex increases with an increase in the aspect ratio. Lower DAR cavities are found to be having the maximum turbulent kinetic energy (TKE) and turbulent production, which is further confirmed by the TKE spectra shown at the point of maximum turbulent production on the symmetrical mid-plane. The power spectra maintain a slope of −53 in the inertial subrange as proposed by Kolmogorov and show a steeper slope in the dissipating range. The time integral scale shows that in low DAR cavities, eddies are formed and undergo complete distortion more frequently. The joint probability density function confirms the anisotropy in turbulence, and the anisotropy invariant map (Lumley triangle) shows the type of turbulent anisotropy which shows whether the turbulence is either one-component or two-component near the walls.

Flow simulation and experimental study of a dynamic asymmetric impinging stream

Classical impinging stream technology can effectively enhance heat and mass transfer and is widely used in various chemical fields. The energy of a particle is rapidly reduced after penetrating the reverse jet due to the fluid resistance in a steady symmetrical impinging stream reactor; thus, the effective particle motion range is restricted. In this paper, we propose a new dynamic asymmetrical impinging stream reactor with dynamic sinusoidal variation in the inlet velocity. We investigated the flow field structure and characteristics of the dynamic asymmetric impinging stream reactor based on numerical simulation and experimental verification. The impingement surface was instantaneously moving in the axial region of the impinging stream reactor, thereby increasing the range of motion of the main active area. In this paper, we discuss the axial turbulent kinetic energy distribution and single particle motion behavior in the context of a dynamic asymmetrical impinging stream with an instantaneously moving impinging surface. In the simulation, the maximum turbulence kinetic energy was still located in the impingement region in the dynamic asymmetric impinging stream reactor (in agreement with that of the steady symmetric impinging stream technology), and the position variation in the maximum turbulent kinetic energy was consistent with that of the impinging surface. In addition, the notable improvements in the particle residence time and motion distance in the main active area have obvious practical advantages in engineering compared with using steady symmetrical impinging stream technology.