Turbulent flow characteristics responsible for current-induced scour around a complex pier

2021 ◽  
Author(s):  
Priyanka Gautam ◽  
T I Eldho ◽  
B. S. Mazumder ◽  
M. R. Behera
Keyword(s):  
Reynolds Number ◽  
Spectral Analysis ◽  
Turbulent Flow ◽  
Vortex Shedding ◽  
Flow Characteristics ◽  
Acoustic Doppler Velocimeter ◽  
Reynolds Stresses ◽  
Velocity Data ◽  
Pile Cap ◽  
Upward Moving

This study investigates the turbulent flow characteristics around a complex pier (CP) with elliptical pile cap, for understanding the mechanics of flow responsible for current-induced scour. The velocity data are recorded using an acoustic Doppler velocimeter (ADV) for a Reynolds number of 67,745. This study gives mean velocities in horizontal and vertical planes, Reynolds stresses, turbulent kinetic energy, and spectral analysis around the CP, which are not addressed earlier. The streamwise spectra with vortex-shedding frequencies and corresponding Strouhal numbers are focused on three distinct regions generated by CP. The elliptical pile-cap shields the downward flow at the upstream of the column, and the upward-moving wakes at the downstream of the CP, responsible for the sediment entrainment around a pier. On comparison, the effect of perturbed flow around the CP is considerably less than that of the simple pier (SP), resulting in less scour around the CP with identical flow situations.

scholarly journals Numerical Study of Flow Characteristics Around Confined Cylinder using OpenFOAM

2018 ◽  
Vol 7 (4.35) ◽  
pp. 617
Author(s):  
P. Mathupriya ◽  
L. Chan ◽  
H. Hasini ◽  
A. Ooi
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Vortex Formation ◽  
Plane Channel ◽  
Flow Characteristics ◽  
Strong Interactions ◽  
Two Dimensional ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency

The numerical study of the flow over a two-dimensional cylinder which is symmetrically confined in a plane channel is presented to study the characteristics of vortex shedding. The numerical model has been established using direct numerical simulation (DNS) based on the open source computational fluid dynamics (CFD) code named OpenFOAM. In the present study, the flow fields have been computed at blockage ratio, β of 0.5 and at Reynolds number, Re of 200 and 300. Two-dimensional simulations investigated on the effects of Reynolds number based on the vortex formation and shedding frequency. It was observed that the presence of two distinct shedding frequencies appear at higher Reynolds number due to the confinement effects where there is strong interactions between boundary layer, shear layer and the wake of the cylinder. The range of simulations conducted here has shown to produce results consistent with that available in the open literature. Therefore, OpenFOAM is found to be able to accurately capture the complex physics of the flow.

Direct simulations of low-Reynolds-number turbulent flow in a rotating channel

1993 ◽  
Vol 256 ◽  
pp. 163-197 ◽  
Author(s):  
Reidar Kristoffersen ◽  
Helge I. Andersson
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Complete Suppression ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Computational Mesh ◽  
Developed Pressure ◽  
Rotating Channel

Direct numerical simulations of fully developed pressure-driven turbulent flow in a rotating channel have been performed. The unsteady Navier–Stokes equations were written for flow in a constantly rotating frame of reference and solved numerically by means of a finite-difference technique on a 128 × 128 × 128 computational mesh. The Reynolds number, based on the bulk mean velocity Um and the channel half-width h, was about 2900, while the rotation number Ro = 2|Ω|h/Um varied from 0 to 0.5. Without system rotation, results of the simulation were in good agreement with the accurate reference simulation of Kim, Moin & Moser (1987) and available experimental data. The simulated flow fields subject to rotation revealed fascinating effects exerted by the Coriolis force on channel flow turbulence. With weak rotation (Ro = 0.01) the turbulence statistics across the channel varied only slightly compared with the nonrotating case, and opposite effects were observed near the pressure and suction sides of the channel. With increasing rotation the augmentation and damping of the turbulence along the pressure and suction sides, respectively, became more significant, resulting in highly asymmetric profiles of mean velocity and turbulent Reynolds stresses. In accordance with the experimental observations of Johnston, Halleen & Lezius (1972), the mean velocity profile exhibited an appreciable region with slope 2Ω. At Ro = 0.50 the Reynolds stresses vanished in the vicinity of the stabilized side, and the nearly complete suppression of the turbulent agitation was confirmed by marker particle trackings and two-point velocity correlations. Rotational-induced Taylor-Görtler-like counter-rotating streamwise vortices have been identified, and the simulations suggest that the vortices are shifted slightly towards the pressure side with increasing rotation rates, and the number of vortex pairs therefore tend to increase with Ro.

An Expression of Reynolds Stresses in Turbulent Lubrication Theory

1992 ◽  
Vol 114 (1) ◽  
pp. 57-60 ◽  
Author(s):  
A. K. Tieu ◽  
P. B. Kosasih
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Turbulent Flow ◽  
Low Reynolds Number ◽  
Stress Gradient ◽  
Lubrication Theory ◽  
Mixing Length ◽  
Reynolds Stresses ◽  
Shear Stress Gradient ◽  
Low Reynolds

This paper proposes an alternative model of Reynolds stresses for turbulent lubrication theory. The approach relies on Prandtl’s mixing length theory which is based on a modified Van Driest mixing formula [1]. However, unlike the previous theories [2, 3] the proposed equation is capable of accounting for the effect of shear stress gradient on the mixing length. Thus it is well suited to turbulent flow analysis in bearings where the presence of shear stress gradient due to the effect of pressure gradient should be considered. A series of velocity measurements in thin channels in the low Reynolds number turbulent flow range are analysed using the theory. The data analysis shows a strong effect of shear stress gradient on the viscous sublayer in the low Reynolds number regime. As a result, a new model of mixing length applicable to the turbulent lubrication analysis in thin film at low or high Reynolds numbers or under low or high shear stress gradient is presented.

Heat and mass transfer from rotating cones

1963 ◽  
Vol 17 (1) ◽  
pp. 105-112 ◽  
Author(s):  
C. L. Tien ◽  
D. T. Campbell
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Heat And Mass Transfer ◽  
Flow Characteristics ◽  
Sublimation Rate ◽  
Semi Empirical ◽  
Good Agreement

Heat transfer by convection from isothermal rotating cones is investigated experimentally by measuring the sublimation rate from naphthalene-coated cones and using the analogy between heat and mass transfer. Measurements are made for a range of conditions from entirely laminar flow to conditions when the outer 70% of the surface area is covered by turbulent flow. Mass-transfer measurements for laminar flow over cones of vertex angles 180°, 150°, 120° and 90° are in good agreement with the theoretical prediction. For turbulent flow, experimental results for cones of the above vertex angles also agree very well with the semi-empirical analogy calculations for the disk case. A different heat- and mass-transfer relationship with the rotational Reynolds number is observed in the measurements on the 60° cone, and is believed to be due to a change of flow characteristics. The instability and the transition of flows over different cone models are also discussed.

Experimental Investigation of Flow Laminarization in a Graphite Flow Channel at High Pressure and High Temperature

2017 ◽  
Author(s):  
Francisco I. Valentín ◽  
Narbeh Artoun ◽  
Masahiro Kawaji
Keyword(s):  
Reynolds Number ◽  
High Temperature ◽  
Turbulent Flow ◽  
Flow Channel ◽  
Transitional Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Reynolds Stresses ◽  
Frequency Spectra ◽  
Flow Laminarization

Hot wire anemometer (HWA) measurements of turbulent gas flow have been performed in upward forced convection experiments at pressures ranging from 0.6 MPa to 6.3 MPa and fluid temperatures ranging from 293 K to 673 K. The results are relevant to deteriorated turbulent heat transfer (DTHT) and flow laminarization in strongly heated gas flows which could occur in gas-cooled Very High Temperature Reactors. The HWA signals were analyzed to directly confirm the occurrence of flow laminarization phenomenon due to strong heating. An X-probe was used to collect radial and axial velocity fluctuation data for pressurized air and pure nitrogen flowing through a circular 16.8 mm diameter flow channel in a 2.7 m long graphite test section for local Reynolds numbers varying from 500 to 22,000. Analyses of the Reynolds stresses and turbulence frequency spectra were carried out and used as indicators of laminar, transition or fully turbulent flow conditions. Low Reynolds stresses indicated the existence of laminar or transitional flow until the local Reynolds number reached a large value, ∼11,000 to 16,000, much higher than the conventional Re = 4,000–5,000 for transition to fully turbulent flow encountered in pipe flows. The critical Reynolds number indicating the completion of transition approximately doubled as the pressure was increased from 0.6 MPa to 2.8 MPa.

scholarly journals Numerical Analysis of Turbulent Flow over a 2-D Prolate Spheroid

2019 ◽  
Vol 8 (4) ◽  
pp. 4646-4651
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Turbulent Flow ◽  
Flow Characteristics ◽  
Prolate Spheroid ◽  
External Flow ◽  
Complex Phenomenon ◽  
Convective Flux ◽  
Viscous Forces ◽  
Laminar And Turbulent Flow

Recently external flow over body creates more interest of study because flow characteristics are dominated by complex phenomenon like separation and transition.in this paper turbulent flow over a 2-D prolate spheroid (6:1) is consider for analysis. Generation of surface grid around prolate spheroid by using grid generation code MESHGEN. Laminar and turbulent Flow past given geometry is simulated by Navier-stoke code RANS3D by second order upwind scheme for convective flux discretization by k-ε model for different Reynolds number, angles of attack .It is observed that the value of drag coefficient is lower than that of a cylinder due to its more streamlined contour. The variation of Cd was steeper in the laminar range than the turbulent range due to the effects of viscous forces being greater in laminar flow.

Numerical investigation of semifilled-pipe flow

2021 ◽  
Vol 932 ◽  
Author(s):  
Julian Brosda ◽  
Michael Manhart
Keyword(s):  
Shear Stress ◽  
Free Surface ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Pipe Flow ◽  
Flow Characteristics ◽  
Streamwise Vorticity ◽  
Reynolds Stresses ◽  
Data Set ◽  
Wall Shear

This study describes turbulent flow in a semifilled pipe with a focus on its secondary currents. To the authors’ knowledge, we provide the first highly resolved data-set for semifilled-pipe flow using direct numerical simulation. The flow parameters range from $Re_\tau =115$ , just maintaining turbulence, to moderate turbulent flow at $Re_\tau =460$ . Some of the main flow characteristics are in line with previously published results from experiments, such as the velocity-dip phenomenon, the main secondary flow and the qualitative distribution of the Reynolds stresses in the core of the flow. We observe some flow phenomena which have not yet been reported in the literature so far for this type of flow. Among those is the inner secondary cell in the mixed corner between the free surface and the pipe's wall, which plays a major role in the distribution of the wall shear stress along the perimeter. We observe that the position and extension of the inner vortex scale with the wall shear stress and those of the outer vortex scale with outer variables. For the first time, we present and discuss distributions of the complete Reynolds stress tensor and its anisotropy which gives rise to the generation of mean streamwise vorticity in a small region in the mixed corners of the pipe. Mean secondary kinetic energy, however, is generated at the free surface around the stagnation point between the inner and outer vortices. This generation mechanism is in line with a vortex dynamics mechanism proposed in the literature.

Experimental Investigation on Flows in a Corrugated Channel

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Efe Ünal ◽  
Hojin Ahn ◽  
Esra Sorguven
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
High Speed ◽  
Rectangular Channel ◽  
Vortex Formation ◽  
Bulk Flow ◽  
High Speed Camera ◽  
Reynolds Stresses ◽  
Flat Plates ◽  
Corrugated Channel

Flows in a corrugated channel are investigated by a high-speed camera and a particle image velocimetry (PIV) system. The bottom wall of the rectangular channel was corrugated with periodic grooves while the top wall and two sidewalls were flat plates made of Plexiglas. Flow visualization data from the high-speed camera determine the critical Reynolds number to be around 1500 by examining the stability of the vortex in the groove as well as fluid ejection from the groove. The visualization data for turbulent flow also show how a vortex evolves within the groove and triggers another vortex formation in the subsequent groove, and how fluid ejected from the groove triggers another ejection from the subsequent groove. Thus, strong hydrodynamic interactions are observed between successive corrugations. In addition, PIV data provide the profiles of velocities and Reynolds stresses as a function of Reynolds number. Time-averaged streamlines show that a large, stable vortex exists in the groove for laminar flow. On the other hand, for turbulent flow, the vortex is unstable inside the groove, often prompting fluid ejection which interacts with the bulk flow. Especially the Reynolds stress of the square of velocity fluctuation in the direction normal to the bulk flow significantly increases as the fluid ejection from the groove intensifies with increasing Reynolds number.

scholarly journals Numerical Computations for Flow Patterns and Force Statistics of Three Rectangular Cylinders

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hamid Rahman ◽  
Shams-ul-Islam ◽  
Waqas Sarwar Abbasi ◽  
Raheela Manzoor ◽  
Fazle Amin ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Flow Characteristics ◽  
Drag And Lift Coefficients ◽  
Aspect Ratios ◽  
Spacing Ratio ◽  
Drag And Lift ◽  
Rectangular Cylinders

In this work, numerical simulations are performed in order to study the effects of aspect ratio (AR) and Reynolds number (Re) on flow characteristics of three side-by-side rectangular cylinders for fixed spacing ratio ( g ), using the lattice Boltzmann method (LBM). The Reynolds number varies within the range 60 ≤ Re ≤ 180, aspect ratio is between 0.25 and 4, and spacing ratio is fixed at g  = 1.5. The flow structure mechanism behind the cylinders is analyzed in terms of vorticity contour visualization, time-trace analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and variations of mean drag coefficient, and Strouhal number. For different combinations of AR and Re, the flow is characterized into regular, irregular, and symmetric vortex shedding. In regular and symmetric vortex shedding the drag and lift coefficients vary smoothly while reverse trend occurs in irregular vortex shedding. At small AR, each cylinder experiences higher magnitude drag force as compared to intermediate and large aspect ratios. The vortex shedding frequency was found to be smaller at smaller AR and increased with increment in AR.

scholarly journals Analyzing the Turbulent Flow Characteristics by Utilizing k-ϵ Turbulence Model.

2017 ◽  
Vol 2 (11) ◽  
pp. 28
Author(s):  
Md. Safayet Hossain ◽  
Md. Ishtiaque Hossain ◽  
Somit Pramanik ◽  
Dr. Jamal Uddin Ahamed
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Skin Friction Coefficient ◽  
Working Fluid ◽  
Turbulent Dissipation ◽  
Quadrilateral Elements ◽  
Fully Developed Turbulent Flow

This study attempts to illustrate the behavior of a fully developed turbulent flow by using k-ε turbulence model. A two dimensional smooth bend channel is adopted for this experiment and water was chosen as working fluid. The Reynolds number was gradually increased to predict the diversity in turbulent kinetic energy (TKE), turbulent dissipation rate, turbulent intensity and eddy viscosity. Primarily the flow has been solved by employing three distinct k-ϵ turbulence models namely, Standard, Renormalization-group (RNG) and Realizable model. After experimenting with ten different sample (from 74E03 to 298E03) of Reynolds numbers, each of these analyses explicitly showed that Standard k-ε model gives much higher value of any aforementioned turbulent properties with respect to other two equation turbulence models. Later it’s been discovered that TKE obtained from Standard k-ω model is almost same as Realizable k-ε model (for Re=298E03, the difference is about 1.8%). It has been observed that the skin friction coefficient at the bend region obtained from different two equation models (Standard, Realizable and RNG k-ϵ model and Standard k-ω model) are almost similar to each other for each sample of Reynolds number. Quadrilateral elements were taken into consideration for grid generation in this analysis. Also, to decrease cost and to achieve further accuracy as well as reduced time consumption mapped faced meshing was utilized.

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