A Numerical Study of Metachronal Propulsion at Low to Intermediate Reynolds Numbers

Inspired by the forward swimming of long-tailed crustaceans, we study an underwater propulsion mechanism for a swimming body with multiple rigid paddles attached underneath undergoing cycles of power and return strokes with a constant phase-difference between neighboring paddles, a phenomenon known as metachronal propulsion. To study how inter-paddle phase-difference affects flux production, we develop a computational fluid dynamics model and a numerical algorithm based on the immersed boundary method, which allows us to simulate metachronal propulsion at Reynolds numbers (RE) ranging from close to 0 to about 100. Our main finding is that the highest average flux is generated when nearest-neighbor paddles maintain an approximate 20%–25% phase-difference with the more posterior paddle leading the cycle; this result is independent of stroke frequency across the full range of RE considered here. We also find that the optimal paddle spacing and the number of paddles depend on RE; we see a qualitative transition in the dynamics of flow generated by metachronal propulsion as RE rises above 80. Roughly speaking, in terms of average flux generation, a tight paddle spacing is preferred when RE is less than 10, but a wider spacing becomes clearly favored when RE is close to or above 100. In terms of efficiency of flux generation, at RE 0.1 the maximum efficiency occurs at two paddles, and the efficiency decreases as the number of paddles increases. At RE 100 the efficiency increases as the number of paddles increases, and it appears to saturate by eight paddles, whereas using four paddles is a good tradeoff for both low and intermediate RE.

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Three regimes of inertial focusing for spherical particles suspended in circular tube flows

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.325 ◽

2019 ◽

Vol 871 ◽

pp. 952-969 ◽

Cited By ~ 3

Author(s):

Saki Nakayama ◽

Hiroshi Yamashita ◽

Takuya Yabu ◽

Tomoaki Itano ◽

Masako Sugihara-Seki

Keyword(s):

Circular Tube ◽

Numerical Study ◽

Reynolds Numbers ◽

Tube Diameter ◽

Spherical Particles ◽

Immersed Boundary ◽

Cross Sectional ◽

Inertial Focusing ◽

Critical Reynolds Numbers ◽

The Cross

An experimental and numerical study on the inertial focusing of neutrally buoyant spherical particles suspended in laminar circular tube flows was performed at Reynolds numbers ($Re$) ranging from 100 to 1000 for particle-to-tube diameter ratios of ${\sim}0.1$. In the experiments, we measured the cross-sectional distribution of particles in dilute suspensions flowing through circular tubes several hundreds of micrometres in diameter. In the cross-section located at 1000 times the tube diameter from the tube inlet, all particles were highly concentrated on one annulus or two annuli, depending on $Re$. At low $Re$, the particles were focused on the so-called Segré–Silberberg (SS) annulus, in accordance with previous studies (regime (A)). At higher $Re$, two particle focusing annuli appeared, with the outer annulus corresponding to the SS annulus (regime (B)). We call the annulus closer to the tube centre ‘the inner annulus’, although this term was used by Matas et al. (J. Fluid Mech., vol. 515, 2004, pp. 171–195) for a significantly broader annulus which included the transient accumulation of particles observed in regime (A). At even higher $Re$, particles were focused on the inner annulus (regime (C)), indicating that the radial position of the SS annulus is no longer a stable equilibrium position. These experimental results were confirmed by a numerical simulation based on the immersed boundary method. The results of this study also indicate that the critical Reynolds numbers between two neighbouring regimes decrease with the increase of the particle-to-tube diameter ratio.

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An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2006-90006 ◽

2006 ◽

Cited By ~ 3

Author(s):

Michael Maurer ◽

Jens von Wolfersdorf ◽

Michael Gritsch

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Thermal Performance ◽

Pressure Loss ◽

Numerical Study ◽

Rectangular Channel ◽

Reynolds Numbers ◽

Transfer Enhancement ◽

High Reynolds Numbers ◽

High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

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Numerical study on swirl cooling flow, heat transfer and stress characteristics based on fluid-structure coupling method under different swirl chamber heights and Reynolds numbers

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2021.121228 ◽

2021 ◽

Vol 173 ◽

pp. 121228

Author(s):

Hong-Wei Li ◽

Yin-Feng Gao ◽

Chang-He Du ◽

Wen-Peng Hong

Keyword(s):

Heat Transfer ◽

Numerical Study ◽

Reynolds Numbers ◽

Coupling Method ◽

Fluid Structure ◽

Cooling Flow ◽

Swirl Chamber ◽

Flow Heat

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Analogue tuning of particle focusing in elasto-inertial flow

Meccanica ◽

10.1007/s11012-021-01329-z ◽

2021 ◽

Author(s):

I. Banerjee ◽

M. E. Rosti ◽

T. Kumar ◽

L. Brandt ◽

A. Russom

Keyword(s):

Numerical Simulations ◽

Cross Section ◽

Immersed Boundary Method ◽

Circular Cross Section ◽

Finite Size ◽

Reynolds Numbers ◽

Immersed Boundary ◽

Particle Focusing ◽

Inertial Flow ◽

Particle Behaviour

AbstractWe report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.

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A numerical study of fractional order population dynamics model

Results in Physics ◽

10.1016/j.rinp.2021.104456 ◽

2021 ◽

pp. 104456

Author(s):

H. Jafari ◽

R.M. Ganji ◽

N.S. Nkomo ◽

Y.P. Lv

Keyword(s):

Population Dynamics ◽

Fractional Order ◽

Numerical Study ◽

Dynamics Model ◽

Population Dynamics Model

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A numerical study of fish adaption behaviors in complex environments with a deep reinforcement learning and immersed boundary–lattice Boltzmann method

Scientific Reports ◽

10.1038/s41598-021-81124-8 ◽

2021 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Yi Zhu ◽

Fang-Bao Tian ◽

John Young ◽

James C. Liao ◽

Joseph C. S. Lai

Keyword(s):

Lattice Boltzmann Method ◽

Lattice Boltzmann ◽

Prey Capture ◽

Numerical Study ◽

Benchmark Problems ◽

Immersed Boundary ◽

Complex Environments ◽

Fish Model ◽

Point To Point ◽

Boltzmann Method

AbstractFish adaption behaviors in complex environments are of great importance in improving the performance of underwater vehicles. This work presents a numerical study of the adaption behaviors of self-propelled fish in complex environments by developing a numerical framework of deep learning and immersed boundary–lattice Boltzmann method (IB–LBM). In this framework, the fish swimming in a viscous incompressible flow is simulated with an IB–LBM which is validated by conducting two benchmark problems including a uniform flow over a stationary cylinder and a self-propelled anguilliform swimming in a quiescent flow. Furthermore, a deep recurrent Q-network (DRQN) is incorporated with the IB–LBM to train the fish model to adapt its motion to optimally achieve a specific task, such as prey capture, rheotaxis and Kármán gaiting. Compared to existing learning models for fish, this work incorporates the fish position, velocity and acceleration into the state space in the DRQN; and it considers the amplitude and frequency action spaces as well as the historical effects. This framework makes use of the high computational efficiency of the IB–LBM which is of crucial importance for the effective coupling with learning algorithms. Applications of the proposed numerical framework in point-to-point swimming in quiescent flow and position holding both in a uniform stream and a Kármán vortex street demonstrate the strategies used to adapt to different situations.

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A Method of Full-Range Gas Concentration Detection Based on Multi-frequency Ultrasonic Cross-cycle Phase Difference Measurement

IEEE Access ◽

10.1109/access.2021.3068200 ◽

2021 ◽

pp. 1-1

Author(s):

Hui Sun ◽

Yunbo Shi ◽

Xin Ding ◽

Xibo Ding ◽

Haibin Wu

Keyword(s):

Phase Difference ◽

Full Range ◽

Cycle Phase ◽

Gas Concentration ◽

Difference Measurement

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Electrodynamics of a magnet moving through a conducting pipe

Canadian Journal of Physics ◽

10.1139/p06-065 ◽

2006 ◽

Vol 84 (4) ◽

pp. 253-271 ◽

Cited By ~ 16

Author(s):

M Hossein Partovi ◽

Eliza J Morris

Keyword(s):

Drag Force ◽

Eddy Currents ◽

Numerical Study ◽

Full Range ◽

Magnetic Behavior ◽

Integral Form ◽

Asymptotic Formulas ◽

Pipe Material ◽

Point Dipole ◽

Axially Symmetric

The popular demonstration involving a permanent magnet falling through a conducting pipe is treated as an axially symmetric boundary-value problem. Specifically, Maxwell's equations are solved for an axially symmetric magnet moving coaxially inside an infinitely long, conducting cylindrical shell of arbitrary thickness at nonrelativistic speeds. Analytic solutions for the fields are developed and used to derive the resulting drag force acting on the magnet in integral form. This treatment represents a significant improvement over existing models, which idealize the problem as a point dipole moving slowly inside a pipe of negligible thickness. It also provides a rigorous study of eddy currents under a broad range of conditions, and can be used for magnetic braking applications. The case of a uniformly magnetized cylindrical magnet is considered in detail, and a comprehensive analytical and numerical study of the properties of the drag force is presented for this geometry. Various limiting cases of interest involving the shape and speed of the magnet and the full range of conductivity and magnetic behavior of the pipe material are investigated and corresponding asymptotic formulas are developed.PACS Nos.: 81.70.Ex, 41.20.–q, 41.20.Gz

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A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

Journal of Heat Transfer ◽

10.1115/1.3245674 ◽

1983 ◽

Vol 105 (4) ◽

pp. 862-869 ◽

Cited By ~ 15

Author(s):

R. S. Amano ◽

M. K. Jensen ◽

P. Goel

Keyword(s):

Heat Transfer ◽

Numerical Solutions ◽

Numerical Study ◽

Separated Flow ◽

Flow Region ◽

Reynolds Numbers ◽

Turbulent Heat ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

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