scholarly journals Turbulent Characteristics and Air Entrainment Patterns in Breaking Surge Waves

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 422
Author(s):  
Zhuoran Li ◽  
Akash Venkateshwaran ◽  
Shooka Karimpour
Keyword(s):  
Sudden Change ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Quadrant Analysis ◽  
Concentration Profiles ◽  
Air Concentration ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Turbulent Characteristics ◽  
3D Flows

Breaking surge waves are highly turbulent three-dimensional (3D) flows, which occur when the water flow encounters a sudden change in depth or velocity. The 3D turbulent structures across a breaking surge are induced by the velocity gradient across the surge and phase discontinuity at the front. This paper examined the turbulent structures in breaking surge waves with Froude numbers of 1.71 and 2.13 by investigating the air entrainment and perturbation patterns across the surge front. A combination of the Volume Of Fluid (VOF) method and Large Eddy Simulation (LES) was utilized to capture air entrainment and turbulent structures simultaneously. The 3D nature of the vortical structures was simulated by implementing a spanwise periodic boundary. The water surface perturbation and air concentration profiles were extracted, and the averaged air concentration profiles obtained from the numerical simulations were consistent with laboratory observations reported in the literature. The linkage between turbulent kinetic energy distribution and air entrainment was also explored in this paper. Finally, using quadrant analysis and the Q-criterion, this paper examined the role of the spanwise perturbations in the development of turbulent structures in the surge front.

scholarly journals Numerical Investigation of Powered Jet Effects by RANS/LES Hybrid Methods

2019 ◽  
Vol 37 (3) ◽  
pp. 565-571
Author(s):  
Zhibin Gong ◽  
Jie Li ◽  
Jixiang Shan ◽  
Heng Zhang
Keyword(s):  
Numerical Investigation ◽  
Hybrid Methods ◽  
Three Dimensional ◽  
Jet Flow ◽  
Weno Scheme ◽  
Detached Eddy Simulation ◽  
Turbulent Structures ◽  
Ambient Flow ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

For the high-precision simulation of engine jet effects, an improved delayed detached eddy simulation (IDDES) method based on the two-equation shear stress transport (SST) model is developed, and the fifth-order finite-volume weighted essentially non-oscillatory (WENO) scheme is employed to enhance accuracy of spatial discretization, and then numerical investigation of powered jet effects by RANS/LES hybrid methods is carried out. The effects of the grid distributions and the accuracy of the spatial schemes are discussed during the RANS/LES validation analysis on the fully expanded jet flow and Acoustic Reference Nozzle (ARN) jet flow. The results show that, by enlarging the grid density and improving the accuracy of the spatial schemes, the velocity distributions in the jet flow can be better predicted, the non-physical steady flow after the jet nozzle can be shortened, the instantaneous flow structures are clearer and the turbulent intensities are more accurate. Then IDDES simulation of turbofan engine jet flow is carried out. The mixing characteristics of the external fan jet flow and internal core jet flow as well as the ambient flow are obtained, and the three-dimensional turbulent structures are also given.

Effect of bridge pier induced turbulence on vegetated meander river morphology

2021 ◽  
Author(s):  
Suresh Modalavalasa ◽  
Vinay Chembolu ◽  
Ketan Kumar Nandi ◽  
Vinayak Kulkarni ◽  
Subashisa Dutta
Keyword(s):  
Transverse Velocity ◽  
Three Dimensional ◽  
Main Channel ◽  
Bridge Pier ◽  
Bridge Piers ◽  
Turbulent Structures ◽  
Meandering Channel ◽  
Turbulent Characteristics ◽  
Sinuous Channel ◽  
The Difference

<p>A natural riverine corridor has several curls based on its physical and geomorphological characteristics. In most of the scenarios, the bridge construction on a meandering channel aligns along the convergent section. The enhanced secondary flow at convergent sections and the effect of meandering curvature bring the complexity in river turbulent characteristics. This effect may become predominant inside the main channel with variability in size and shape of the bridge pier. The present work discusses the turbulent structures in the main channel due to the variability in pier diameter (1inch and 2 inch ϕ) and a number of bridge piers on floodplain with inclusive of vegetation. Three-dimensional flow vertical and transverse velocity measurements were carried with acoustic Doppler velocimeter (ADV) 100Hz, at apex cross-section in a low sinuous channel. The results of the analysis showed that the combined effect of pier and vegetation on floodplain significantly altered the shear layer mechanisms in the channel with varying flow patterns. The comparison of the difference in secondary velocities between the pier with 1 inch and 2 inch ϕ  is 57% more in the case of lesser diameter pier. Further, the effect of size and number of piers on transverse velocity, Reynold’s shear stress is more susceptible to the mainstream. The convergence induced contraction of the meandering channel along with the bridge pier on its floodplain is observed to affect the turbulent structures formed in the main channel.</p>

scholarly journals Three-Dimensional Aerators: Characteristics of the Air Bubbles

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1430
Author(s):  
Shuai Li ◽  
Jianmin Zhang ◽  
Xiaoqing Chen ◽  
Jiangang Chen
Keyword(s):  
Three Dimensional ◽  
Flow Region ◽  
Air Entrainment ◽  
Chord Length ◽  
Air Concentration ◽  
Bubble Frequency ◽  
Cross Sectional ◽  
Frequency Distributions ◽  
Air Bubble ◽  
Flow Features

Three-dimensional aerators are often used in hydraulic structures to prevent cavitation damage via enhanced air entrainment. However, the mechanisms of aeration and bubble dispersion along the developing shear flow region on such aerators remain unclear. A double-tip conductivity probe is employed in present experimental study to investigate the air concentration, bubble count rate, and bubble size downstream of a three-dimensional aerator involving various approach-flow features and geometric parameters. The results show that the cross-sectional distribution of the air bubble frequency is in accordance with the Gaussian distribution, and the relationship between the air concentration and bubble frequency obeys a quasi-parabolic law. The air bubble frequency reaches an apex at an air concentration (C) of approximately 50% and decreases to zero as C = 0% and C = 100%. The relative location of the air-bubble frequency apex is 0.210, 0.326 and 0.283 times the thickness of the layers at the upper, lower and side nappes, respectively. The air bubble chord length decreases gradually from the air water interface to the core area. The air concentration increases exponentially with the bubble chord length. The air bubble frequency distributions can be fit well using a “modified” gamma distribution function.

On the Unsteady and Turbulent Characteristics of the Three-Dimensional Shear-Driven Cavity Flow

1994 ◽  
Vol 116 (3) ◽  
pp. 439-449 ◽  
Author(s):  
S. A. Jordan ◽  
S. A. Ragab
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Cavity Flow ◽  
Complex Flow ◽  
Driven Cavity ◽  
Eddy Simulation ◽  
Turbulent Characteristics ◽  
Moderate Reynolds Number ◽  
Flow Features ◽  
Driven Cavity Flow

The three-dimensional shear-driven cavity flow is numerically investigated at Reynolds numbers of 5000 and 10000. This investigation focuses on the unsteadiness and turbulent characteristics of the flow. At the moderate Reynolds number (Re = 5000) where the cavity flow is fully laminar, a direct numerical simulation (DNS) is used whereas large-eddy simulation (LES) methodology is adopted to predict the cavity flow at the higher Reynolds number (Re = 10000). Establishing a suitable form for the subgrid scale (SGS) turbulence model in this complex flow is guided by the DNS results at Re = 5000. Additionally, the SGS model is verified against DNS results at Re = 7500 where the cavity flow is known through experimentation to be locally transitional. The LES results verify the published experimental evidence as well as uncover new flow features within the cavity.

scholarly journals Application of VOF and k-ε turbulence model in simulation of flow over a bottom aerated ramp and step structure

Water SA ◽  
2019 ◽  
Vol 45 (2 April) ◽  
Author(s):  
Talia Tokyay ◽  
Can Kurt
Keyword(s):  
Flow Direction ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Single Step ◽  
Air Concentration ◽  
Two Phase ◽  
Cross Sectional ◽  
Ansys Fluent ◽  
Jet Length ◽  
Logarithmic Decay

A three-dimensional numerical model of ANSYS, Fluent (2011) was employed for studying mid to high discharge supercritical two-phase flow over a single slope spillway with a single step for aeration of the flow. In this study 18 simulations were conducted using the Volume of Fluid (VOF) method for air-water interface tracking and simple k-ɛ model for turbulence closure. Submerged circular shaped pipes located at the bottom of the step were utilized as aerators. Analyses concentrate on the air-entrainment phenomenon and jet-length of the flow from the step to the re-attachment point. The variables considered in the study are discharge, aerator size, different aerator arrangements, Froude number of the flow, presence of a ramp before the step and its angle. Observed jet-length values in this study were compared with two sets of empirical formulae from literature for code validation. Cross-sectional average of air concentration due to bottom aeration was determined in the streamwise direction downstream of the re-attachment of the jet. The air concentration is observed to follow a logarithmic decay in the flow direction within the de-aeration zone.

scholarly journals Prediction of flow resistance in a compound open channel

2013 ◽  
Vol 16 (1) ◽  
pp. 19-32 ◽  
Author(s):  
Mrutyunjaya Sahu ◽  
S. S. Mahapatra ◽  
K. C. Biswal ◽  
K. K. Khatua
Keyword(s):  
Flow Resistance ◽  
Open Channel ◽  
Sudden Change ◽  
Flood Plain ◽  
Compound Channel ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Flow Prediction ◽  
Large Eddy ◽  
Artificial Neural Network Ann

Flooding in a river is a complex phenomenon which affects the livelihood and economic condition of the region. During flooding flow overtops the river course and spreads around the flood plain resulting in a two-course compound channel. It has been observed that the flow velocity in the flood plain is slower than that in the actual river course. This can produce a large shear layer between sections of the flow and produces turbulent structures which generate extra resistance and uncertainty in flow prediction. Researchers have adopted various numerical, analytical, and empirical models to analyze this situation. Generally, a one-dimensional empirical model is used for flow prediction assuming that the flow in the compound open channel is uniform. However, flow in a compound channel is quasi-uniform due to the transfer of momentum in sub-sections and sudden change of depths laterally. Hence, it is essential to analyze the turbulent structures prevalent in the situation. Therefore, in this study, an effort has been made to analyze the turbulent structure involved in flooding using large eddy simulation (LES) method to estimate the resistance. Further, a combination of an artificial neural network (ANN) and a fuzzy logic (FL) is considered to predict flow resistance in a compound open channel.

scholarly journals Three-dimensional Large Eddy Simulation of air entrainment under plunging breaking waves

2006 ◽  
Vol 53 (8) ◽  
pp. 631-655 ◽  
Author(s):  
Pierre Lubin ◽  
Stéphane Vincent ◽  
Stéphane Abadie ◽  
Jean-Paul Caltagirone
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals Investigation of Pressure Oscillation and Cavitation Characteristics for Submerged Self-Resonating Waterjet

2021 ◽  
Vol 11 (15) ◽  
pp. 6972
Author(s):  
Lihua Cui ◽  
Fei Ma ◽  
Tengfei Cai
Keyword(s):  
Sudden Change ◽  
Three Dimensional ◽  
Pressure Oscillation ◽  
Experimental Tests ◽  
Low Pressure ◽  
The Self ◽  
Two Phase ◽  
Cavitation Phenomenon ◽  
Pressure Zone ◽  
Unsteady Characteristics

The cavitation phenomenon of the self-resonating waterjet for the modulation of erosion characteristics is investigated in this paper. A three-dimensional computational fluid dynamics (CFD) model was developed to analyze the unsteady characteristics of the self-resonating jet. The numerical model employs the mixture two-phase model, coupling the realizable turbulence model and Schnerr–Sauer cavitation model. Collected data from experimental tests were used to validate the model. Results of numerical simulations and experimental data frequency bands obtained by the Fast Fourier transform (FFT) method were in very good agreement. For better understanding the physical phenomena, the velocity, the pressure distributions, and the cavitation characteristics were investigated. The obtained results show that the sudden change of the flow velocity at the outlet of the nozzle leads to the forms of the low-pressure zone. When the pressure at the low-pressure zone is lower than the vapor pressure, the cavitation occurs. The flow field structure of the waterjet can be directly perceived through simulation, which can provide theoretical support for realizing the modulation of the erosion characteristics, optimizing nozzle structure.

Sign in / Sign up

Export Citation Format

Share Document