Variation Of Turbulent Kinetic Energy Research Articles

Computational Study on Influence Factors and Vortical Structures in Static Drift Tests

This paper conducted a computational study on the KCS benchmark model at static drift conditions. At the first instance, the roles played by the grid size, turbulence model, and time step are qualitatively and quantitatively analyzed with the orthogonal experimental method (OEM). After the verification of simulated results compared with experimental data in a Static Oblique Towing Test (OTT), hydrodynamic performance is obtained with the employment of the SST κ-ω turbulence model. The grid size is set as 0.07 m while the time step as 0.01 s. The characteristics of the wake field are illustrated in different forms, such as contours of the free surface, distribution of pressure and hydrodynamic forces, variation of turbulent kinetic energy (TKE), and so on. For a deep insight into the physical mechanisms of the asymmetrical flow field, the Detached Eddy Simulation (DES) method is also utilized to capture vortical structures occurring around the hull, in comparison with results obtained through the Reynolds Averaged Navier Stokes (RANS) model. With the aim of a hydrodynamic derivative estimation or detailed flow characteristics analysis, corresponding selections of the computational method are disparate.

Effect of Vortex Generator on Gas Turbine Blade Cooling

The current numerical study suggests using a vortex generator to lessen the consequences of a counter-rotating vortex pair. For this inquiry, the delta winglet pair in the common-flow-down arrangement is selected. A suitable model for turbulence is examined. The x, y, and z vorticity is studied. Additionally, the effect of variations in turbulent kinetic energy is examined. The outcome is contrasted with the reference scenario. Employing the k-omega SST turbulence model and the commercial code FLUENT, numerical analysis is accomplished.

Turbulence effect on total mechanical energy budget and energy loss of turbulent flows with different hydraulic regimes in open-channel transitions

ABSTRACT In this study, a modified form of the total mechanical energy budget equation is developed for 3-D turbulent flows with different hydraulic regimes in open-channel transitions, from which the effect of all turbulence parameters can be evaluated by applying some equalizations and RANS numerical simulations. The total energy equation is also used to extract an explicit relationship for energy loss based on turbulence parameters. The findings are presented in the form of the application of the relationship to calculate the energy loss based on simulation results for subcritical turbulent flow and hydraulic jump in open-channel transitions, which leads to identifying the effect of non-homogeneity and anisotropy of turbulence on flow energy balance. The results show that the work done by viscous shear stresses, the viscous diffusion of turbulence, and the turbulent diffusion have little to no effect on the total mechanical energy budget of open-channel turbulent flows; instead, the effect of the variations of turbulent kinetic energy and the work done by turbulence stresses is more significant. The benefit of using the modified energy equation is demonstrated by the potential for evaluating the details that were not previously considered.

Turbulence properties of a vertical round jet in a wavy-crossflow environment

The discharge of wastewater into coastal waters can be simplified as a turbulent jet under waves and currents. A laboratory study has been carried out to measure the instantaneous flow field of a vertical round jet under wavy-crossflow environment using an improved particle image velocimetry (PIV) technique. The phase-averaged streamlines are found to be the most chaotic at the wave trough phase. Temporal variation in fluctuating turbulent kinetic energy is explored. Results indicate a lack of distinctive patterns in fluctuation turbulent kinetic energy across wave phases, particularly in far field. This suggests that wave phases marginally affect jet width expansion, especially in the far field. Spatial variations in turbulent kinetic energy are examined and crossflow and wave period are also considered. It is found that decreasing relative wave-orbital velocity to crossflow velocity Rwc enhances maximum turbulent kinetic energy in the near field of the wavy-crossflow jet.

Experimental and Numerical (Fluent-VOF, k-ϵ, DPM) Study of Variation of Trap Efficiency of Irregular Hexagonal SIT (Sediment Invert Trap) for Particle Removal in Rectangular Open Drains and Sewers

At some locations along the length of open sewers and drains, sediment particles get deposited on the bottom bed, reducing hydraulic efficiency. A sediment invert trap (SIT) can be implemented on the bottom of open sewers and drains to trap sediment particles moving on the bed surface. Several investigators have conducted experimental and computational studies to understand the particle trapping behavior of invert traps of various shapes and depths under varying sediment and flow parameters. In experimental studies, previous investigators have used actual and artificial sediment particles; in computational analyses, spherical particles have been considered. The current study investigated the particle trapping behavior of an irregular hexagonal sediment invert trap (SIT) through experiments and two-dimensional (2D) numerical modeling. Seventy-two experiments were performed using actual sewage solid particles in an open rectangular channel with a bottom-fitted invert trap with multiple depths. Sixty numerical simulations were performed using ANSYS Fluent 2020 R1 computational fluid dynamics (CFD) software, considering spherical and nonspherical sewage solid particles. The velocity field was predicted using the volume of fluid (VOF) model combined with the realizable k-ϵ turbulence model. Particle trap efficiency was predicted using a stochastic discrete phase model (DPM). Trap efficiency varied significantly with depth of flow, invert trap depth, slot aperture size, and particle size and shape. Analysis of the simulated flow field showed that variation of turbulent kinetic energy above the trap’s slot aperture was also responsible for variations in trap efficiency values. Fluent simulations considering particles as nonspherical (using shape factors) agreed well with experimentally measured trap efficiency, with mean absolute percentage errors (MAPE) of 6.23%, 8.79%, and 13.77% for particle size ranges SS1, SS2, and SS3, respectively, with both slot apertures at all flow depths. The 2D-CFD study consistently overpredicted trap efficiencies compared to the experimental findings. With a fixed length and width of 0.32 and 0.15 m, respectively, the optimal depth of the irregular hexagonal SIT was found to be 0.65 m with slot aperture sizes of 0.15 and 0.03 m, whereas with slot aperture size of 0.15 m only, invert trap depths equal to 0.58, 0.43, and 0.38 m was found as optimum.

Experimental and numerical study on the wave attenuation performance and dynamic response of kelp-box type floating breakwater

As a kind of marine plant, kelp plays an important role in the improvement of marine environment. In addition, kelp arrays exhibit a great potential for wave attenuation. In this paper, a kelp-box type floating breakwater is proposed and experimental studies are carried out. Firstly, comparative experimental studies of the wave attenuation performance of kelp-box type floating breakwater with different kelp lengths, planting intervals and the number of rows of kelp arrangements are conducted. Secondly, the mooring force and motion responses of kelp-box type floating breakwater with different arrangements of kelp are compared exhaustively. Finally, a numerical model of the interaction between wave and kelp-box type floating breakwater is set up. The mechanism of wave energy dissipation is analyzed based on the velocity field, evolution of vorticity and turbulent kinetic energy around the kelp-box type floating breakwater. The results indicate that kelp improves the wave dissipation capacity of box floating breakwater. And kelp-box type floating breakwater with longer kelp lengths, denser planting intervals and more rows of planting exhibits better wave attenuation performance, especially for long waves. In addition, variations in turbulent kinetic energy and shedding of vortices are the main causes of wave dissipation of kelp-box type floating breakwater.

Differences of turbulence modulation by heavy particles on solid wall and erodible bed surface

In this paper, wall-resolved large-eddy simulation of turbulence, Lagrangian point-force model of particle tracking, and two-way coupling approach are used to simulate the particle-laden flow over a rigid wall. The flow is a turbulent open channel flow with the particle-free friction Reynolds number of Reτ=4200. Together with the simulated results over an erodible bed from Zheng et al. [J. Fluid Mech. 918, 1–27 (2021)], the influence of the lower boundary condition of particle motion with the wall-normal gravity on turbulence modulation is thoroughly compared. It is found that high-inertia (St+=244.5) particles studied in this work moving over a rigid wall increase the mean fluid velocity and the scales of turbulence structures away from the wall, suppress turbulence fluctuations and Reynolds stress, and reduce the scales of turbulence structures near the wall as compared with the particle-free flow. Gravitational settling of particles accounts for most of the changes, and the crossing trajectory caused by particles bouncing near the rigid wall is responsible for the reduction of the scales of the near-wall turbulence structures. On the contrary, the splashing process of particles over the erodible bed leads to the decrease in the mean fluid velocity, the anisotropic variation of turbulent kinetic energy, the shrink of the outer turbulence structure, and the enlargement of the near-wall streaks. The results reveal the significance of the near-wall particle motion (rebound or splashing) on turbulence modulation.

Variation of turbulent kinetic energy due to dimples in intake manifold for diesel engine

This work compares the application of spherical dimples in a modified intake manifold for the diesel engine to a normal intake manifold in terms of turbulent kinetic energy. In this work spherical dimples having an h/d ratio of 0.5 are used. These dimples had been designed by using designing tools in the design modeler module of ANSYS. Same bend angle condition 60° degree from the axis of manifold had been taken for both modified and normal intake system. The main purpose of this work is to observe the variation in turbulent kinetic energy due to the incorporation of spherical dimples in a intake model with a 20 mm diameter, 200 mm length and with a bend around 160 mm length. In this flow dynamics parameters other than turbulent kinetic energy like velocity and pressure were also observed. All numerical analyses were carried out on the FLUENT module of ANSYS and significant improvements of 25.45% and 35.41% for partial and full dimpled surface were reported in turbulent kinetic energy with respect to normal intake manifold, which were obtained due to modifications in the intake system. This work provides path to develop new techniques for enhancing mixing in the diesel engine.

Study of turbulent flow past a square cylinder using partially-averaged Navier–Stokes method in OpenFOAM

The present paper reports numerical simulation of turbulent flow over a square cylinder using a novel scale resolving computational fluid dynamics technique named Partially-Averaged Navier–Stokes (PANS), which bridges Reynolds-Averaged Navier–Stokes (RANS) with Direct Numerical Simulation (DNS) in a seamless manner. All stream-wise and wall normal mean velocity components, turbulent stresses behavior have been computed along the flow (streamwise) as well as in transverse (wall normal) direction. The measurement locations are chosen based on the previous studies so that results could be compared. However, the Reynolds number ( Re) of the flow is maintained at 21,400 and K– ω turbulence model is considered for the present case. All the computations are performed in OpenFOAM framework using a finite volume solver. Additionally, turbulent kinetic energy variations are presented over a wide range of measurement planes in order to explain the energy transfer process in highly unsteady turbulent flow field. The fluctuating root mean square velocities in the streamwise as well as in the wall normal direction have been discussed in the present work. It has been found that Partially-Averaged Navier–Stokes (PANS) model is capable of capturing the properties of highly unsteady turbulent flows and gives better results than Reynolds-Averaged Navier–Stokes (RANS). The results obtained using Partially-Averaged Navier–Stokes (PANS) are quite comparable with Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) data available in literature. The partially-averaged Navier–Stokes results are compared with our simulated Reynolds-Averaged Navier–Stokes (RANS) results, available experimental as well as numerical results in literature and it is found to be good in agreement.

Turbulent fluid flow and heat transfer analysis of heated rectangular blocks encountered in electronics enclosures

Computational investigation of steady, two-dimensional heat transfer attributes for forced convective chaotic discharge in a vertical channel of cluster of heated rectangular sections is performed. The discharge is deemed to be periodic fully developed so that the issue is determined for two extending zone and explanation is developed to more number of sections. This structure reproduces the driven convective cooling of a cluster of engraved circuit panels confronted in computerize belongings. Two mathematical statements for k- ℇ model is used for modeling for the turbulence and the finite volume methodology is used. Computations are performed for Reynolds numbers ranging from 6000-12000, Prandtl number of 0.7 and various geometric parameters characterizing the problem. As Reynolds number steps up the Nusselt Number increases. Re-circulations undermine the local Nusselt number when matched with comparing variation from a identical plate. The velocity contours, temperature distributions, variation of turbulent kinetic energy and kinetic energy dissipation rates in a vertical channel is found. With the blocks in the cluster, pressure fall is higher in resemblance to plane duct.

Numerical study of air-water two-phase flow in a two-dimensional vertical helical channel

In this study, air-water two-phase flow patterns in a two-dimensional vertical helical channel are investigated. The simulations are performed using OpenFOAM software. The single-fluid method and Eulerian−Eulerian approach are used to solve the governing equations. The paper focuses on different flow patterns based on the change in the apparent velocity of water and air, and the influence of volume fraction of the air at the entrance of the channel. The variations of turbulent kinetic energy, volume fraction and velocity profile are presented. The range of air and water apparent velocities at the channel entrance is 0.05–10 m s−1 and 0.1–1.5 m s−1, respectively. According to the results, four flow patterns including bubbly, churn, turbulent, and annular are observed. It is demonstrated that for the bubbly regime, the values of volume fraction of phases are close to unity. When the air inlet velocity is very high, the two-phase flow forms the annular flow pattern.

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.

On assessment of heat transfer deterioration of a channel with supercritical n-decane for scramjet engines cooling

To explore the local heat transfer deterioration (HTD) behavior in cooling channels with the endothermic hydrocarbon fuel for a scramjet engine, the flow and thermal performance of a rectangular channel cooled by supercritical hydrocarbon fuel are analyzed in detail, especially at the region of the heated wall. A 3D geometrical model is simulated under a SST k-ω turbulence model to validate results which agrees well with available experimental data. The critical variations of turbulent kinetic energy and representative thermo-physical properties are selected to assess the internal mechanism of HTD in terms of the deteriorative point of the wall temperature and the heat transfer coefficient. This study reveals that the occurrence of HTD is strongly affected by the variation of turbulent kinetic energy, and that the local HTD behavior is considered to be induced by the laminar flow caused by thermal acceleration effect.

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.

Comparison of mixing layer heights determined using LiDAR, radiosonde, and numerical weather prediction model at a rural site in southern India

ABSTRACTThere is no agreed reference method for accurately determination of mixing layer height (MLH) in the existing literature. In part, this is due to different definitions of the atmospheric boundary layer exist, depending on the quantities and the physical processes invoked. In addition, MLH during late afternoon transition period is highly challenging to determine and perform model simulations because of the rapid variations in turbulent kinetic energy. For the first time, MLH has been determined at remote tropical site of Gadanki, India (13.45°N, 79.17°E, 360 masl) using ground-based elastic backscatter LiDAR (EBL). This article focuses on the late afternoon transition period and compares it with MLH obtained from the EBL to concurrent radiosonde (RS) observations [MLH (RS)] and numerical models. Five different techniques have been applied to the EBL backscatter profiles for the determination of MLH. The mean of the five methods agreed to within 15% with the RS-derived MLH under various synoptic conditions at the site. This indicates the potential capability of continuous monitoring of MLH by our EBL system. However, MLH determined by Weather Research and Forecasting model and European Center for Medium-Range Weather Forecasts Re Analaysis (ERA)-interim reanalysis systematically underestimated of the MLH (LiDAR) by about 62% and 48%, respectively. The mean growth rate of diurnal evolution of MLH was found to about 120 and 200 m h−1 during winter and spring seasons, respectively.

Time Variability of Surface-Layer Characteristics over a Mountain Ridge in the Central Himalayas During the Spring Season

We present the diurnal variations of surface-layer characteristics during spring (March–May 2013) observed near a mountain ridge at Nainital ( $$29.4^{\circ }\mathrm{N},\,79.5^{\circ }\mathrm{E},$$ 1926 m above mean sea level), a hill station located in the southern part of the central Himalayas. During spring, this region generally witnesses fair-weather conditions and significant solar heating of the surface, providing favourable conditions for the systematic diurnal evolution of the atmospheric boundary layer. We mainly utilize the three-dimensional wind components and virtual temperature observed with sonic anemometers (sampling at 25 Hz) mounted at 12- and 27-m heights on a meteorological tower. Tilt corrections using the planar-fit method have been applied to convert the measurements to streamline-following coordinate system before estimating turbulence parameters. The airflow at this ridge site is quite different from slope flows. Notwithstanding the prevalence of strong large-scale north-westerly winds, the diurnal variation of the mountain circulation is clearly discernible with the increase of wind speed and a small but distinct change in wind direction during the afternoon period. Such an effect further modulates the surface-layer water vapour content, which increases during the daytime and results in the development of boundary-layer clouds in the evening. The sensible heat flux (H) shows peak values around noon, with its magnitude increasing from March $$(222\pm 46\,\mathrm{W\,m}^{-2})$$ to May $$(353\pm 147\,\mathrm{W\,m}^{-2}).$$ The diurnal variation of turbulent kinetic energy (e) is insignificant during March while its mean value is enhanced by 30–50 % of the post-midnight value during the afternoon (1400–1600 IST), delayed by $${\approx }2\,\mathrm{h}$$ compared to the peak in H. This difference between the phase variations of incoming shortwave flux, H and e primarily arise due to the competing effects of turbulent eddies produced by thermals and wind shear, the latter increase significantly with time until nighttime during April–May. Variations of the standard deviations of vertical wind normalized with friction velocity $$(\sigma _\mathrm{w}/u_{*})$$ and temperature normalized with scaling temperature $$(\sigma _{\theta }/T_{*})$$ as functions of stability parameter (z / L) indicate that they follow a power-law variation during unstable conditions, with an index of 1/3 for the former and −1/3 for the latter. The coefficients defining the above variations are found in agreement with those derived over flat as well as complex terrain.

Salt intrusion at a submarine spring in a fringing reef lagoon

AbstractVariations in discharge and turbulent kinetic energy (TKE) were studied at a point‐source submarine groundwater discharge (SGD), within a fringing reef lagoon, from quadrature (neap) to syzygy (spring) tides. The principal factors affecting discharge and TKE variations were tides and waves. Field data indicated discharge, and TKE varied with high and low tides, and with quadrature and syzygy. Maximum discharge and TKE values were observed during low tides when the hydrostatic pressure over the jet was minimal, while the lowest discharge and TKE values were found at high tides. Syzygy tides produced consistent saltwater intrusion during high tides, while quadrature tides produced the greatest TKE values. In general, as the discharge intensified during low tides, jet temperatures decreased suggesting that waters originated further within the aquifer. At the same time jet salinities increased, suggesting a mixing of aquifer and seawater. To reconcile these two seemingly opposing views, it is proposed that the jet conduit is connected to a stratified chamber with seawater below brackish water. The greatest subtidal discharge occurred during quadrature tides. Syzygy produced low subtidal discharge driven by flow reversals (flow into the aquifer) observed throughout syzygy high tides in conjunction with the peak wave setup (>5 cm) observed during a storm. While tides were the primary driving force of the discharge, waves played a nonnegligible role. Wave effects on the discharge were most evident during syzygy high tides combined with a storm, when the subtidal spring discharge was weakest and salt intrusion developed.

망간단괴 집광기 주위 해수 유동교란 수치해석

Seawater flow characteristics around a manganese nodule mining device in deep sea were analyzed through numerical investigation. The mining device influences the seawater flow field with complicated velocity distributions, and they are largely dependent on the seawater flow speed, device moving speed, and injection velocity from the collecting part. The flow velocity and turbulent kinetic energy distributions are compared at several positions from the device rear, side, and top, and it is possible to predict the distance from which the mining device affects the seawater flow field through the variation of turbulent kinetic energy. With the operation of the collecting device the turbulent kinetic energy remarkably increases, and it gradually decreases along the seawater flow direction. Turbulent kinetic energy behind the mining system increases with the seawater flow velocity. The transient behavior of nodule particles, which are not collected, is also predicted. This study will be helpful in creating an optimal design for a manganese nodule collecting device that can operate efficiently and which is eco-friendly.

Variations in turbulent kinetic energy at a point source submarine groundwater discharge in a reef lagoon

The influence of sea level variations due to tides and wave setup on turbulent kinetic energy (TKE) was observed at a point source submarine groundwater discharge in a fringing coral reef lagoon. Tidal and wave setup variations modulated speed, TKE, TKE dissipation, and water temperature and salinity at the buoyant jet. The primary driver of jet TKE and speed variations was tides, while wave setup was a minor contributor. An inverse relationship between surface elevation and TKE was explained with an exponential equation based on sea level variations. During low tides, peak jet speeds (up to 0.3 m s−1) and TKE per unit mass (up to 0.4 m2 s−2) were observed. As high tide approached, the jet produced minimum TKE of ~0.003 m2 s−2 and TKE dissipation ranged from 2 to 8×10−4 m2 s−3. This demonstrated the sensitivity of the jet discharge to tides despite the small tidal range (<20 cm). Jet temperatures and salinities displayed semidiurnal oscillations with minimum salinity and temperature values during maximum discharge. Jet salinities increased throughout low tides while temperatures decreased. This pattern suggested the jet conduit was connected to a stratified cavity within the aquifer containing cool fresh water over cool salty water. As low tides progressed, jet outflow increased in salinity because of the mixing within the conduit, while lower jet temperatures suggested water coming from further or deeper in the aquifer. The presence of such a cavity has been recently confirmed by divers.

Ensemble simulations to investigate the impact of large‐scale urbanization on precipitation in the lower reaches of Yangtze River Valley, China

AbstractThe influence of urban clusters in the lower reaches of Yangtze River Valley (YRV) on a summertime heavy precipitation event is evaluated based on ensemble simulations using the Weather Research and Forecasting (WRF) model. Results show that control runs with realistic representation of urban areas perform better than the sensitivity runs with urban areas replaced by cropland, suggesting that the urban canopy physics in the surface layer, and hence realistic urban land‐use classification, is crucial for urban‐induced precipitation modelling. Precipitation starts later but is stronger due to the urban effects. Urbanization leads to two adjacent belts of increasing and decreasing precipitation to the north of the Yangtze River. These urban‐induced variations in precipitation are attributed to the impact of urban clusters in the lower reaches of the YRV, which act like a single large (non‐continuous) city to slow down the precipitation process due to its building barrier effect. Such an impact leads to more precipitation in the north of the precipitation field but provides less moisture for precipitation in the south. The variations of turbulent kinetic energy and vorticity that resulted from the effects of urban clusters show upward propagation during the precipitation event, suggesting that the urbanization impact may be transferred from surface to upper atmosphere, which could exert important influences on precipitation processes.