scholarly journals Study of a Rock-Ramp Fish Pass with Staggered Emergent Square Obstacles

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1175
Author(s):  
Flavia Cavalcanti Miranda ◽  
Ludovic Cassan ◽  
Pascale Laurens ◽  
Tien Dung Tran
Keyword(s):  
Velocity Field ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Design Process ◽  
Water Depth ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Fish Passage ◽  
Lower Velocity ◽  
Water Depths

A rock-ramp fish passage with square obstacles was experimentally and numerically studied in this work with the objective of investigating in detail the hydraulic behind such fishways and to evaluate the importance of the shape of the obstacles. The LES and VOF methods were used for the simulations, and for the measurements, shadowgraphy and ADV were applied. Two different validations were successfully performed. In the first one, the experimental and numerical results of a chosen case were compared in detail. In the second validation, the focus was given to the stage-discharge. Following the validation, a numerical study was carried out to point out the differences in the flow characteristics from a configuration with square and circular obstacles. The discharge was nearly the same for both configurations, which implies different water depths. The results showed a lower velocity field, lower turbulent kinetic energy, and lower lateral fluctuations for the configuration with square blocks, which indicated a better passability for this geometry. However, it also presented a higher water depth, which led to a less attractive discharge. The differences in the flow generated in the two configurations indicated that the shape is an important modifiable parameter to be considered in the design process.

scholarly journals Budgets of Turbulent Kinetic Energy and Reynolds Normal Stresses in Coaxial Jets with and Without Swirl: A Numerical Study

2020 ◽  
Vol 9 ◽  
pp. 32-42
Author(s):  
Pravin Ananta Kadua ◽  
Yasuhiko Sakaib ◽  
Yasumasa Itob ◽  
Koji Iwanob ◽  
Masatoshi Suginob ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Numerical Study ◽  
Normal Stresses ◽  
Coaxial Jets

scholarly journals Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1481
Author(s):  
Xinrui Li ◽  
Zhenggui Li ◽  
Baoshan Zhu ◽  
Weijun Wang
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Flow Instability ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

scholarly journals NUMERICAL SIMULATION OF TURBULENT WAVE BOUNDARY LAYERS

1986 ◽  
Vol 1 (20) ◽  
pp. 119 ◽  
Author(s):  
J.H. Trowbridge ◽  
C.N. Kanetkar ◽  
N.T. Wu
Keyword(s):  
Velocity Field ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Boundary Layers ◽  
Second Order ◽  
Minor Role ◽  
Steady Streaming ◽  
Stokes Waves ◽  
A Minor ◽  
Wave Boundary

This paper reports numerical computations of fully rough turbulent boundary layers produced by first and second order Stokes waves. The computations are based on a mixing length turbulence closure and on a slightly more sophisticated turbulent kinetic energy closure. The first order results compare well with existing laboratory results. Reversal of the second order steady streaming under relatively long waves, which has been predicted analytically, is also predicted in the numerical results, The steady second order velocity field is found to become fully established only after a development time on the order of a few hundred wave periods. Both the first and second order results indicate that advection and diffusion of turbulent kinetic energy play a minor role in determining the Reynolds averaged velocity field.

scholarly journals Free surface profile and inception point as characteristics of aerated flow over stepped spillway: Numerical study

2019 ◽  
Vol 42 (1) ◽  
pp. 42-48
Author(s):  
Chakib Bentalha ◽  
Mohammed Habi
Keyword(s):  
Free Surface ◽  
Kinetic Energy ◽  
Water Depth ◽  
Numerical Study ◽  
Surface Profile ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Ansys Fluent ◽  
Vof Model ◽  
Inception Point

Abstract Stepped spillway is hydraulic structure designed to dissipate the excess in kinetic energy at the downstream of dams and can reduce the size of stilling basin at the toe of the spillway or chute. The flow on a stepped spillway is characterised by the large aeration that can prevent or reduce the cavitation damage. The air entrainment starts where the boundary layer attains the free surface of flow; this point is called “point of inception”. Within this work the inception point is determined by using software Ansys Fluent where the volume of fluid (VOF) model is used as a tool to track the free surface thereby the turbulence closure is derived in the k − ε turbulence standard model. This research aims to find new formulas for describe the variation of water depth at step edge and the positions of the inception point, at the same time the contour map of velocity, turbulent kinetic energy and strain rate are presented. The found numerical results agree well with experimental results like the values of computed and measured water depth at the inception point and the numerical and experimental inception point locations. Also, the dimensionless water depth profile obtained by numerical method agrees well with that of measurement. This study confirmed that the Ansys Fluent is a robust software for simulating air entrainment and exploring more characteristics of flow over stepped spillways.

scholarly journals A CFD-based procedure for airspace integration of small unmanned aircraft within congested areas

2017 ◽  
Vol 9 (4) ◽  
pp. 235-252 ◽  
Author(s):  
Craig WA Murray ◽  
David Anderson
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Flow Characteristics ◽  
Unmanned Aircraft ◽  
Prevailing Wind ◽  
A Posteriori ◽  
Vehicle Performance ◽  
Inlet Velocity ◽  
Congested Area ◽  
The City

Future integration of small unmanned aircraft within an urban airspace requires an a posteriori understanding of the building-induced aerodynamics which could negatively impact on vehicle performance. Moving away from generalised building formations, we model the centre of the city of Glasgow using Star-CCM+, a commercial CFD package. After establishing a critical turbulent kinetic energy for our vehicle, we analyse the CFD results to determine how best to operate a small unmanned aircraft within this environment. As discovered in a previous study, the spatial distribution of turbulence increases with altitude. It was recommended then that UAVs operate at the minimal allowable altitude within a congested area. As the flow characteristics in an environment are similar, regardless of inlet velocity, we can determine areas within a city which will have consistently low or high values of turbulent kinetic energy. As the distribution of turbulence is dependent on prevailing wind directions, some directions are more favourable than others, even if the wind speed is unchanging. Moving forward we should aim to gather more information about integrated aircraft and how they respond to turbulence in a congested area.

scholarly journals Effect of Baffles on the Sloshing in Road Tankers Carrying LPG: A Comparative Numerical Study

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
J. L. Bautista-Jacobo ◽  
E. Rodríguez-Morales ◽  
J. J. Montes-Rodríguez ◽  
H. Gámez-Cuatzín
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Stokes Equations ◽  
Numerical Study ◽  
Interface Velocity ◽  
Vehicle Control ◽  
Navier Stokes ◽  
Type I ◽  
Type Ii ◽  
Navier Stokes Equations

This work presents a comparative numerical study of the effect of using baffles, and its design, on the behavior of sloshing in a partially filled road tanker carrying LPG. Navier-Stokes equations and standardk-εturbulence model are used to simulate fluid movement; the Volume of Fluid (VOF) method is used to track the liquid-gas interface. Velocity distributions, sloshing stabilization times, and contours of turbulent kinetic energy, which are of high importance in choosing the best design of baffles, are shown. The results show sloshing stabilization times of 22 and 21 s for road tankers with cross-shaped (Type I) and X-shaped (Type II) baffles, respectively, finding lower values of turbulent kinetic energy for Type II design, being, therefore, the best design of baffles for damping of sloshing and vehicle control among studied ones.

scholarly journals Experimental and Numerical Study of the Effects of Geometric Appendance Elements on Energy Dissipation over Stepped Spillway

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 957
Author(s):  
Amir Ghaderi ◽  
Saeed Abbasi
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Numerical Study ◽  
Air Entrainment ◽  
Computational Procedure ◽  
Stepped Spillway ◽  
Construction Costs ◽  
Geometric Configurations ◽  
Inception Point

In the stepped spillway, the steps, by providing an artificial roughening bed, dissipate the flow of energy more than other types of spillways, so the construction costs for stilling basin are reduced. However, what is important in this type of spillway is increasing the effectiveness of steps in the rate of energy dissipation. The present study deals with experimental and numerical simulations regarding the influence of geometric appendance elements on the steps and its impact on the energy dissipation performances, flow patterns properties, turbulent kinetic energy, flow resistance and the Darcy roughness. The localization of inception point of air entrainment is also assessed. To this aim, different configurations are taken into account. The computational procedure is validated with experimental results and then used to test the hydraulic behavior of different geometric configurations. The results showed that the appendance elements on the steps increased the turbulent kinetic energy (TKE) values and Darcy–Weisbach friction and the energy dissipation increased significantly. By reducing the height of the elements, energy dissipation and the TKE value increase more significantly. With the appendance elements on step, the air entrainment inception locations a positioning further upstream than the flat step stepped spillway.

scholarly journals Experimental determination of tunnel ventilation axial ducted fan performance

2016 ◽  
Vol 20 (1) ◽  
pp. 209-221 ◽  
Author(s):  
Milan Sekularac
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Ventilation System ◽  
Flow Characteristics ◽  
Pollutant Removal ◽  
Reynolds Stresses ◽  
Scaled Model ◽  
Tunnel Ventilation ◽  
Longitudinal Ventilation ◽  
Traffic Tunnel

To investigate traffic tunnel ventilation flows, a scaled model of a traffic tunnel with longitudinal ventilation system based on ducted fans is used. Flows in tunnels are influenced by tunnel geometry, fan characteristics, ventilation operation scenario, vehicle traffic, atmospheric factors, etc. To analyze flow fields of tunnels in detail, knowledge of tunnel jet-fan properties and turbulent flow characteristics at the fan exit are required, and can be used as input data for CFD boundary conditions of tunnel flow computation. For this purpose experimental measurements were done using the hot wire anemometry technique. The obtained results, trough ensemble-averaged and time averaged profiles of all velocity components, turbulence intensity, turbulent kinetic energy, integral flow length scales, available Reynolds stresses, Turbulent kinetic energy production rates and the fan thrust performance, are presented. These data allow us to analyze in more detail the influence of fan flow on energy and pollutant removal efficiencies of the tunnel ventilation and to evaluate accuracy of CFD studies on fan improvements.

scholarly journals Local turbulent kinetic energy modelling based on Lagrangian stochastic approach in CFD and application to wind energy

2021 ◽  
Author(s):  
Kerlyns Martínez ◽  
Mireille Bossy ◽  
Jean-François Jabir
Keyword(s):  
Kinetic Energy ◽  
Wind Energy ◽  
Stochastic Model ◽  
Turbulent Kinetic Energy ◽  
Flow Characteristics ◽  
Direct Methods ◽  
Physical Parameters ◽  
Uncertainty Distribution ◽  
Deterministic Modelling ◽  
Wind Measurements

<p>In order to better integrate the underlying meteorological processes with the developing technologies within wind energy industry, acquiring relevant statistical information of air motion at a local place, and quantifying the subsequent uncertainty of involved parameters in the models, are fundamental tasks. Special emphasis should be made on the growing interest in energy production forecasting and modelling for wind energy developments that rises the issue of accounting for the uncertain nature of the local forecast. Taking this into consideration, we present the construction of an original stochastic model for the instantaneous turbulent kinetic energy at a given point of a flow, and we validate estimator methods on this model with observational data examples from annual historic of a 10 Hz anemometer wind measurements. <br>More precisely, starting from the viewpoint of Lagrangian modelling of the wind in the boundary layer, we establish a mathematical link between 3D+time computational fluid dynamics (CDF) models for turbulent near-wall flows and stochastic time series models by deriving a family of mean-field dynamics featuring the square norm of the turbulent velocity. Then, by approximating at equilibrium the characteristic nonlinear terms of the dynamics, we recover the so called Cox-Ingersoll-Ross stochastic model, which was previously suggested in the literature for modelling wind speed. Remarkably, our stochastic model for the instantaneous turbulent kinetic energy is parametrised by physical constants in CFD, which provides a more direct link between the stochastic nature of the underlying processes and the classical physics behind these phenomena. Nevertheless, these physical parameters may vary with the flow characteristics and situations, so we consider it relevant to adjust their values while constructing the forecasts. Such tuning of the physical parameters was previously proposed in the literature from a deterministic modelling context with RANS equations. We then propose a two-step procedure for the calibration of the parameters: a training stage where we construct a priori distribution for the parameter vector using direct methods and wind measurements, and a stage of refinement of the uncertainty distribution using Bayesian inference combined with Markov Chain Monte Carlo sample techniques. In particular, we show the accuracy of the calibration method and the performance of the calibrated model in predicting the wind distribution through the quantification of uncertainty.</p>

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