Tsunami-like flow induced forces on the structure: Dependence of the hydrodynamic force coefficients on Froude number and flow channel width in quasi-steady flow phase

In this paper, we discover the origin of the scaling laws of sediment transport under turbulent flow over a sediment bed, for the first time, from the perspective of the phenomenological theory of turbulence. The results reveal that for the incipient motion of sediment particles, the densimetric Froude number obeys the ‘(1 + σ )/4’ scaling law with the relative roughness (ratio of particle diameter to approach flow depth), where σ is the spectral exponent of turbulent energy spectrum. However, for the bedforms, the densimetric Froude number obeys a ‘(1 + σ )/6’ scaling law with the relative roughness in the enstrophy inertial range and the energy inertial range. For the bedload flux, the bedload transport intensity obeys the ‘3/2’ and ‘(1 + σ )/4’ scaling laws with the transport stage parameter and the relative roughness, respectively. For the suspended load flux, the non-dimensional suspended sediment concentration obeys the ‘ − Z ’ scaling law with the non-dimensional vertical distance within the wall shear layer, where Z is the Rouse number. For the scour in contracted streams, the non-dimensional scour depth obeys the ‘4/(3 − σ )’, ‘−4/(3 − σ )’ and ‘−(1 + σ )/(3 − σ )’ scaling laws with the densimetric Froude number, the channel contraction ratio (ratio of contracted channel width to approach channel width) and the relative roughness, respectively.

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A Double-Bridge Channel Shape of a Membraneless Microfluidic Fuel Cell

Energies ◽

10.3390/en14216973 ◽

2021 ◽

Vol 14 (21) ◽

pp. 6973

Author(s):

Ji-Hyun Oh ◽

Muhammad Tanveer ◽

Kwang-Yong Kim

Keyword(s):

Fuel Cell ◽

Numerical Model ◽

Power Density ◽

Flow Channel ◽

Channel Width ◽

Channel Height ◽

Cross Sectional ◽

Channel Shape ◽

Microfluidic Fuel Cell ◽

Inner Channel

A double-bridge shape is proposed as a novel flow channel cross-sectional shape of a membraneless microfluidic fuel cell, and its electrochemical performance was analyzed with a numerical model. A membraneless microfluidic fuel cell (MMFC) is a micro/nano-scale fuel cell with better economic and commercial viability with the elimination of the polymer electrolyte membrane. The numerical model involves the Navier–Stokes, Butler–Volmer, and mass transport equations. The results from the numerical model were validated with the experimental results for a single-bridge channel. The proposed MMFC with double-bridge flow channel shape performed better in comparison to the single-bridge channel shape. A parametric study for the double-bridge channel was performed using three sub-channel widths with the fixed total channel width and the bridge height. The performance of the MMFC varied most significantly with the variation in the width of the inner channel among the sub-channel widths, and the power density increased with this channel width because of the reduced width of the mixing layer in the inner channel. The bridge height significantly affected the performance, and at a bridge height at 90% of the channel height, a higher peak power density of 171%was achieved compared to the reference channel.

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Simulation of Flow Around a Cube at Moderate Reynolds Numbers Using the Lattice Boltzmann Method

Journal of Fluids Engineering ◽

10.1115/1.4044821 ◽

2019 ◽

Vol 142 (1) ◽

Cited By ~ 1

Author(s):

Majid Hassan Khan ◽

Atul Sharma ◽

Amit Agrawal

Keyword(s):

Reynolds Number ◽

Drag Coefficient ◽

Lattice Boltzmann Method ◽

Steady Flow ◽

Flow Regime ◽

Lattice Boltzmann ◽

Reynolds Numbers ◽

Side Force ◽

Force Coefficients ◽

Boltzmann Method

Abstract This article reports flow behavior around a suspended cube obtained using three-dimensional (3D) lattice Boltzmann method (LBM)-based simulations. The Reynolds number (Re) range covered is from 84 to 770. Four different flow regimes are noted based on the flow structure in this range of Re: steady axisymmetric (84 ≤ Re ≤ 200), steady nonaxisymmetric (215 ≤ Re ≤ 250), unsteady nonaxisymmetric in one plane and axisymmetric in the other plane (276 ≤ Re ≤ 300), and unsteady nonaxisymmetric in streamwise orthogonal planes (339 ≤ Re ≤ 770). Recirculation length and drag coefficient follow inverse trend in the steady flow regime. The unsteady flow regime shows hairpin vortices for Re ≤ 300 and then it becomes structureless. The nature of force coefficients has been examined at various Reynolds numbers. Temporal behavior of force coefficients is presented along with phase dependence of side force coefficients. The drag coefficient decreases with increase in Reynolds number in the steady flow regime and the side force coefficients are in phase. Drag coefficients are compared with established correlations for flow around a cube and a sphere. The side force coefficients are perfectly correlated at Re = 215 and they are anticorrelated at Re = 250. At higher Reynolds numbers, side force coefficients are highly uncorrelated. This work adds to the existing understanding of flow around a cube reported earlier at low and moderate Re and extends it further to unsteady regime at higher Re.

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Numerical Studies on PEM Fuel Cell with Different Landing to Channel Width of Flow Channel

Procedia Engineering ◽

10.1016/j.proeng.2014.12.437 ◽

2014 ◽

Vol 97 ◽

pp. 1534-1542 ◽

Cited By ~ 14

Author(s):

M. Muthukumar ◽

P. Karthikeyan ◽

M. Vairavel ◽

C. Loganathan ◽

S. Praveenkumar ◽

...

Keyword(s):

Fuel Cell ◽

Pem Fuel Cell ◽

Flow Channel ◽

Channel Width ◽

Numerical Studies

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Impact of a falling jet

Journal of Fluid Mechanics ◽

10.1017/s0022112010001291 ◽

2010 ◽

Vol 657 ◽

pp. 22-35 ◽

Cited By ~ 6

Author(s):

PAUL CHRISTODOULIDES ◽

FRÉDÉRIC DIAS

Keyword(s):

Galerkin Method ◽

Froude Number ◽

Steady Flow ◽

Maximum Pressure ◽

Horizontal Plate ◽

Vertical Pipe ◽

Simplified Models ◽

Free Surfaces ◽

Bernoulli’S Equation ◽

The Impact

Given the complexity of the problem of the impact of a mass of liquid on a solid structure, various simplified models have been introduced in order to obtain some insight on particular aspects of the problem. Here the steady flow of a jet falling from a vertical pipe, hitting a horizontal plate and flowing sideways is considered. Depending on the elevation H of the pipe relative to the horizontal plate and the Froude number F, the flow can either leave the pipe tangentially or detach from the edge of the pipe. When the flow leaves tangentially, it can either be diverted immediately by the plate or experience squeezing before being diverted. First, the problem is reformulated using conformal mappings. The resulting problem is then solved by a collocation Galerkin method; a particular form is assumed for the solution, and certain coefficients in that representation are then found numerically by satisfying Bernoulli's equation on the free surfaces at certain discrete points. The resulting equations are solved by Newton's method, yielding various configurations of the solution based on the values of F and H. The pressure exerted on the plate is computed and discussed. For a fixed value of F, the maximum pressure along the plate goes through a minimum as H increases from small to large values. Results are presented for the three possible configurations: (i) tangential departure from the pipe and no squeezing, (ii) tangential departure from the pipe followed by squeezing of the liquid and (iii) detachment of the liquid from the pipe (with subsequent squeezing).

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Principal Curves for Lumen Center Extraction and Flow Channel Width Estimation in 3-D Arterial Networks: Theory, Algorithm, and Validation

IEEE Transactions on Image Processing ◽

10.1109/tip.2011.2179054 ◽

2012 ◽

Vol 21 (4) ◽

pp. 1847-1862 ◽

Cited By ~ 8

Author(s):

W. C. K. Wong ◽

R. W. K. So ◽

A. C. S. Chung

Keyword(s):

Flow Channel ◽

Channel Width ◽

Principal Curves

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Impact of a rising stream on a horizontal plate of finite extent

Journal of Fluid Mechanics ◽

10.1017/s0022112008004746 ◽

2009 ◽

Vol 621 ◽

pp. 243-258 ◽

Cited By ~ 9

Author(s):

P. CHRISTODOULIDES ◽

F. DIAS

Keyword(s):

Galerkin Method ◽

Froude Number ◽

Steady Flow ◽

Stagnation Point ◽

Critical Value ◽

Horizontal Plate ◽

Free Surfaces ◽

Bernoulli’S Equation ◽

Asymmetric Flows ◽

Finite Extent

The steady flow of a stream emerging from a nozzle, hitting a horizontal plate and falling under gravity is considered. Depending on the length of the plate L and the Froude number F, the plate can either divert the stream or lead to its detachment. First, the problem is reformulated using conformal mappings. The resulting problem is then solved by a collocation Galerkin method; a particular form is assumed for the solution, and certain coefficients in that representation are then found numerically by satisfying Bernoulli's equation on the free surfaces at certain discrete points. The resulting equations are solved by Newton's method, yielding various configurations of the solution based on the values of F and L. The lift exerted on the plate is computed and discussed. If the plate is long enough, physically meaningful solutions are found to exist only for values of F greater than or equal to a certain critical value F0, which is to be determined. Results are presented, both for F > F0 where the detachment is horizontal and for F = F0 where the detachment point is a stagnation point at a 120° corner. Related asymmetric flows where the rising stream is inclined are also studied.

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