scholarly journals Optimal undulatory swimming for a single fish-like body and for a pair of interacting swimmers

2017 ◽  
Vol 813 ◽  
pp. 301-345 ◽  
Author(s):  
Audrey P. Maertens ◽  
Amy Gao ◽  
Michael S. Triantafyllou
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Energy Savings ◽  
Body Motion ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Line Configuration ◽  
Measured Displacement ◽  
Undulatory Swimming ◽  
Carangiform Swimming

We establish through numerical simulation conditions for optimal undulatory propulsion for a single fish, and for a pair of hydrodynamically interacting fish, accounting for linear and angular recoil. We first employ systematic two-dimensional (2-D) simulations to identify conditions for minimal propulsive power of a self-propelled fish, and continue with targeted 3-D simulations for a danio-like fish; all at Reynolds number 5000. We find that the Strouhal number, phase angle between heave and pitch at the trailing edge, and angle of attack are principal parameters. For 2-D simulations, imposing a deformation based on measured displacement for carangiform swimming provides, at best, efficiency of 35 %, which increases to 50 % for an optimized motion; for a 3-D fish, the efficiency increases from 22 % to 34 %. Indeed, angular recoil has significant impact on efficiency, and optimized body bending requires maximum bending amplitude upstream of the trailing edge. Next, we turn to 2-D simulation of two hydrodynamically interacting fish. We find that the upstream fish benefits energetically only for small distances. In contrast, the downstream fish can benefit at any position that allows interaction with the upstream wake, provided its body motion is timed appropriately with respect to the oncoming vortices. For an in-line configuration, one body length apart, the efficiency of the downstream fish can increase from 50 % to 60 %; for an offset arrangement it can reach 80 %. This proves that in groups of fish, energy savings can be achieved for downstream fish through interaction with oncoming vortices, even when the downstream fish lies directly inside the jet-like flow of an upstream fish.

Numerical Study on the Performance of a Micropump with a Wiggling Blade

2005 ◽  
Vol 219 (10) ◽  
pp. 1069-1077
Author(s):  
T Uchiyama ◽  
K Kikuyama
Keyword(s):  
Numerical Simulation ◽  
Finite Element Method ◽  
Reynolds Number ◽  
Numerical Study ◽  
Two Dimensional ◽  
Progressive Wave ◽  
Trailing Edge ◽  
Pump Performance ◽  
Dimensional Finite Element ◽  
Straight Conduit

This study is concerned with the numerical simulation for the performance of a micropump having a wiggling blade. The blade is mounted on a straight conduit, and the wiggling motion is expressed by a progressive wave. The flow in the pump is simulated by the two-dimensional finite element method. The Reynolds number Re, based on the phase velocity of the progressive wave and the blade length, ranges from 10 to 150. The similarity for pump performance appears at Re ≥ 100. However, the pump performance deteriorates with decreasing Re at Re < 100. The time variation of the pump flowrate is found to be very small, demonstrating that the pump can deliver almost steady flow. The simulation also reveals the mechanism of the delivery as follows: The flow heading for the pump outlet occurs near the concave surface of the blade, and it is transported by the progressive wave to the blade trailing edge, and eventually, it is shed from the trailing edge.

Numerical Simulation of Flows in a Pipe with an Aneurismal Sac (Effects of Aneurismal Models and Stents)

2008 ◽  
Vol 33-37 ◽  
pp. 1025-1030
Author(s):  
Gulbahar Wahap ◽  
Tatsuya Kobori ◽  
Yoko Takakura ◽  
Norio Arai ◽  
Yoshifumi Konishi ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Human Blood ◽  
Steady States ◽  
Computational Results ◽  
Two Dimensional ◽  
Blood Flows ◽  
Inflow Condition ◽  
Inflow Conditions ◽  
Two Dimensional Flows

Recently, the intravascular therapy using microcoils and stents to treat aneurysms has attracted researcher’s interest. In this study, in order to evaluate the effects of the stents, a numerical simulation of two-dimensional flows has been carried out for a pipe with a model of an aneurismal sac. Using aneurismal models with different inclined angles to the pipe, inflow conditions with steady states or pulsations have been applied in the range of Reynolds number in human blood flows. First, the computational results are compared with experiments under the steady inflow condition, which has shown the reliability of the numerical simulation. Furthermore, the mechanism of flows with an aneurismal model is discussed in the case with or without a stent, and consequently the effect of the stent is clarified.

scholarly journals Direct Numerical Simulation in Two Dimensional Homogeneous Isotropic Turbulence Using Spectral Method

2013 ◽  
Vol 5 (3) ◽  
pp. 435-445
Author(s):  
M. S. I. Mallik ◽  
M. A. Uddin ◽  
M. A. Rahman
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Flow Field ◽  
Direct Numerical Simulation ◽  
Spectral Method ◽  
Isotropic Turbulence ◽  
Qualitative Behavior ◽  
Two Dimensional ◽  
Homogeneous Isotropic Turbulence ◽  
Decaying Turbulence

Direct numerical simulation (DNS) in two-dimensional homogeneous isotropic turbulence is performed by using the Spectral method at a Reynolds number Re = 1000 on a uniformly distributed grid points. The Reynolds number is low enough that the computational grid is capable of resolving all the possible turbulent scales. The statistical properties in the computed flow field show a good agreement with the qualitative behavior of decaying turbulence. The behavior of the flow structures in the computed flow field also follow the classical idea of the fluid flow in turbulence. Keywords: Direct numerical simulation, Isotropic turbulence, Spectral method. © 2013 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi:http://dx.doi.org/10.3329/jsr.v5i3.12665 J. Sci. Res. 5 (3), 435-445 (2013)  

Two-dimensional impervious sails: experimental results compared with theory

1984 ◽  
Vol 144 ◽  
pp. 445-462 ◽  
Author(s):  
B. G. Newman ◽  
H. T. Low
Keyword(s):  
Reynolds Number ◽  
Dynamic Instability ◽  
Two Dimensional ◽  
Poor Agreement ◽  
Trailing Edge ◽  
Small Incidence ◽  
Visualization Experiments ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Edge Flow

Experiments have been made on quasi two-dimensional sails of small camber and at small incidence. Four excess-length ratios have been tested at a Reynolds number of 1.2 x 105. The results for lift, tension, centre of lift, maximum camber and its position, and leading- and trailing-edge membrane angles have been compared with existing inviscid theories and show poor agreement in general. This is attributed to leading- and trailing-edge flow separations as indicated by supplementary flow-visualization experiments. The optimum incidences in particular are much greater than the theoretical value of 0°. Luffing occurs at slightly negative incidences and appears to be a dynamic instability. The highest lift-to-drag ratio obtained was 16.5 on a membrane with an excess-length ratio of 0.03.

Direct numerical simulation of a puff and a slug in transitional cylindrical pipe flow

1999 ◽  
Vol 387 ◽  
pp. 39-60 ◽  
Author(s):  
H. SHAN ◽  
B. MA ◽  
Z. ZHANG ◽  
F. T. M. NIEUWSTADT
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Pipe Flow ◽  
Leading Edge ◽  
Transition Process ◽  
Axial Position ◽  
Trailing Edge ◽  
Mean Velocity ◽  
The Mean

A direct numerical simulation of transitional pipe flow is carried out with the help of a spectral element method and used to investigate the localized regions of ‘turbulent’ flow that are observed in experiments. Two types of such regions can be distinguished: the puff and the slug. The puff, which is generally found at low values of the Reynolds numbers, is simulated for Re = 2200 where the Reynolds number Re is based on the mean velocity UB and pipe diameter D. The slug occurs at a higher Reynolds number and it is simulated for Re = 5000. The computations start with a laminar pipe flow to which is added a prescribed velocity disturbance at a given axial position and for a finite time. The disturbance then evolves further into a puff or slug structure.The simulations confirm the experimentally observed fact that for a puff the velocity near the leading edge changes more gradually than for a slug where an almost discontinuous change is observed. The positions of the leading and trailing edges of the puff and slug are computed from the simulations as a function of time. The propagation velocity of the leading edge is found to be constant and equal to 1.56UB and 1.69UB for the puff and slug, respectively. For the trailing edge the velocity is found to be 0.73UB and 0.52UB, respectively. By rescaling the simulation results obtained at various times to a fixed length, we define an ensemble average. This method is used to compute the average characteristics of the puff and slug such as the spatial distribution of the mean velocity, the turbulent velocity fluctuations and also the wall shear stress. By computing particle trajectories we have investigated the entrainment and detrainment of fluid by a puff and slug. We find that the puff detrains through its trailing edge and entrains through its leading edge. The slug entrains fluid through its leading and through most of its trailing edge. As a consequence the fluid inside the puff is constantly exchanged with fluid outside whereas the fluid inside a slug remains there. These entrainment/detrainment properties which are in agreement with the measurements of Wygnanski & Champagne (1973) imply that the puff has the characteristics of a wave phenomenon while the slug can be characterized more as a material property which travels with the flow.Finally, we have investigated in more detail the velocity field within the puff. In a coordinate system that travels with the mean velocity we find recirculation regions both near the trailing and leading edges which agrees at least qualitatively with experimental data. We also find streamwise vortices, predominantly in the trailing-edge region which have been also observed in experiments and which are believed to play an important role in the dynamics of the transition process.

scholarly journals Numerical simulation of two-dimensional laminar unsteady flow past a right trapezoidal cylinder at low Reynolds number: study of sharpening angle, time step, grid independence and domain size

2018 ◽  
Vol 192 ◽  
pp. 02030
Author(s):  
Sodsai Lamtharn ◽  
Monsak Pimsarn
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Strouhal Number ◽  
Domain Size ◽  
Two Dimensional ◽  
Time Step ◽  
Flow Past ◽  
The Right ◽  
Grid Independence

Numerical simulation of two-dimensional laminar unsteady flow past a right trapezoidal cylinder at low Reynolds number (Re = 100), zero of the flow approaching angle and sharpening angle of the right trapezoidal of 22.5° with a side ratio B/A = 1 are carried out to provide moreapplicable data for engineering design of barred tee in aspect of structural integrity. A finite volume method, non-uniform meshing with second-order implicit time discretization into eight-node quadratic quadrilateral finite elements is employed. An incompressible flow SIMPLEC code with constant fluid properties is used. The convective terms using a third-order QUICK scheme. The numerical simulation result is compared against the published results of flow past a square cylinder. The effect of sharpening angle on the response of the right trapezoidal cylinder is investigated. A special study of the effects of flow on significant factor for time step, grid independence, blockage ratio, domain size, upstream and downstream extents, size domain next to cylinder and size domain extent are performed systematically. The Strouhal number and RMS lift coefficients of fully saturated flow are calculated. The result shown that increasing of sharpening angle, the Strouhal number is negligible changed whilst the RMS lift coefficients significantly increased.

Three-dimensional MHD flows in rectangular ducts with internal obstacles

2000 ◽  
Vol 418 ◽  
pp. 265-295 ◽  
Author(s):  
B. MÜCK ◽  
C. GÜNTHER ◽  
U. MÜLLER ◽  
L. BÜHLER
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Magnetic Fields ◽  
Interaction Parameter ◽  
Hartmann Number ◽  
Three Dimensional ◽  
Side Length ◽  
Two Dimensional ◽  
The Magnetic Field

This paper presents a numerical simulation of the magnetohydrodynamic (MHD) liquid metal flow around a square cylinder placed in a rectangular duct. In the hydrodynamic case, for a certain parameter range the well-known Kármán vortex street with three-dimensional flow patterns is observed, similar to the flow around a circular cylinder. In this study a uniform magnetic field aligned with the cylinder is applied and its influence on the formation and downstream transport of vortices is investigated. The relevant key parameters for the MHD flow are the Hartmann number M, the interaction parameter N and the hydrodynamic Reynolds number, all based on the side length of the cylinder. The Hartmann number M was varied in the range 0 [les ] M [les ] 85 and the interaction parameter N in the range 0 [les ] N [les ] 36. Results are presented for two fixed Reynolds numbers Re = 200 and Re = 250. The magnetic Reynolds number is assumed to be very small. The results of the numerical simulation are compared with known experimental and theoretical results. The hydrodynamic simulation shows characteristic intermittent pulsations of the drag and lift force on the cylinder. At Re = 200 a mix of secondary spanwise three-dimensional instabilities (A and B mode, rib vortices) could be observed. The spanwise wavelength of the rib vortices was found to be about 2–3 cylinder side lengths in the near wake. At Re = 250 the flow appears more organized showing a regular B mode pattern and a spanwise wavelength of about 1 cylinder side length. With an applied magnetic field a quasi-two-dimensional flow can be obtained at low N ≈ 1 due to the strong non-isotropic character of the electromagnetic forces. The remaining vortices have their axes aligned with the magnetic field. With increasing magnetic fields these vortices are further damped due to Hartmann braking. The result that the ‘quasi-two-dimensional’ vortices have a curvature in the direction of the magnetic field can be explained by means of an asymptotic analysis of the governing equations. With very high magnetic fields the time-dependent vortex shedding can be almost completely suppressed. By three-dimensional visualization it was possible to show characteristic paths of the electric current for this kind of flow, explaining the action of the Lorentz forces.

scholarly journals Some characteristics of the resultant air flow from motions induced by ventilation and heat source in a two-dimensional enclosure

2015 ◽  
Vol 37 (3) ◽  
pp. 177-186
Author(s):  
T. V. Tran ◽  
N. T. Thuy
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Source ◽  
Air Flow ◽  
Stationary Motion ◽  
Two Dimensional ◽  
Different Types ◽  
Heat Amount

Ventilated air flow in an enclosure is often unsteady (turbulent) at even very low Reynolds number (Re). Meantime natural convection in a box is stationary motion at large enough Rayleigh number (Ra). This paper deals with the interaction between two those flows in a two-dimensional room. The room has one inlet and one or two outlets. A heat source locates on the floor. The numerical simulation of the interaction is carried out at some values of Re and Ra for two cases of the inlet and outlet configuration. Some interesting characteristics of the resultant flow are discovered. The heat amount released by the source and removed from the room by different types of this flow is also provided.

Sign in / Sign up

Export Citation Format

Share Document