On the Disappearance of the Steady Wake Region Behind Porous Objects Under Free Stream Flow At Low Reynolds Numbers

2021 ◽  
Author(s):  
Dipankar Chatterjee ◽  
Chandan Kumar
Keyword(s):  
Porous Body ◽  
Quantitative Estimation ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Darcy Number ◽  
The Body ◽  
Complete Disappearance ◽  
Wake Region ◽  
Porosity Parameter ◽  
Porous Bodies

Abstract A solid bluff object produces a recirculating wake region immediately behind it when subjected to flow separation under a steady flow condition. Similar phenomena can also be observed for a porous body. However, unlike the solid object the porous body allows some part of the flow to go through it. A consequence of this flow penetration in porous objects is, the wake behind the body may get reduced in size and detach from the body. The wake even may disappear at some value of the porosity parameter (Darcy number). In this brief article, we compute the critical values of the porosity parameter for complete disappearance of the wake region behind two-dimensional porous bodies of circular and square shapes. A regime diagram is constructed to show the regions of wake formation, its detachment and finally its disappearance around circular and square shaped porous bodies. The critical value of the porosity parameter increases with increasing Reynolds number, and it is found greater for the square body in comparison to the circular one. The study provides a quantitative estimation of how the porosity plays a significant role in demarcating the flow characteristics around porous objects.

Pulsatile pipe flow pseudoplastic materials; The flow enhancement for Re ≪ 1

1983 ◽  
Vol 48 (6) ◽  
pp. 1579-1587 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Small Parameter ◽  
Pipe Flow ◽  
Quantitative Estimation ◽  
Reynolds Numbers ◽  
Power Law Model ◽  
Viscosity Function ◽  
Small Reynolds Numbers ◽  
Title Problem ◽  
Flow Enhancement ◽  
Method Of Small Parameter

Solution of the title problem for the power-law model of viscosity function is constructed by the method of small parameter in the region of small Reynolds numbers. The main result of the paper is a quantitative estimation of the values of Re, when the influence of inertia on flow enhancement may be quite neglected.

A NUMERICAL STUDY ON THE HEMODYNAMIC AND SHEAR STRESS OF DOUBLE ANEURYSM THROUGH S-SHAPED VESSEL

2015 ◽  
Vol 27 (04) ◽  
pp. 1550033 ◽  
Author(s):  
Mahdi Halabian ◽  
Alireza Karimi ◽  
Borhan Beigzadeh ◽  
Mahdi Navidbakhsh
Keyword(s):  
Blood Flow ◽  
Mechanical Behavior ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
The Body ◽  
Sweep Angle ◽  
Abdominal Aortic ◽  
Hemodynamic Characteristics ◽  
Refined Meshes

Abdominal aortic aneurysm (AAA) is a degenerative disease defined as the abnormal ballooning of the abdominal aorta (AA) wall which is usually caused by atherosclerosis. The aneurysm grows larger and eventually ruptures if it is not diagnosed and treated. Aneurysms occur mostly in the aorta, the main artery of the chest and abdomen. The aorta carries blood flow from the heart to all parts of the body, including the vital organs, the legs, and feet. The objective of the present study is to investigate the combined effects of aneurysm and curvature on flow characteristics in S-shaped bends with sweep angle of 90° at Reynolds number of 900. The fluid mechanics of blood flow in a curved artery with abnormal aortic is studied through a mathematical analysis and employing Cosmos flow simulation. Blood is modeled as an incompressible non-Newtonian fluid and the flow is assumed to be steady and laminar. Hemodynamic characteristics are analyzed. Grid independence is tested on three successively refined meshes. It is observed that the abrupt expansion induced by AAA results in an immensely disturbed regime. The results may have implications not only for understanding the mechanical behavior of the blood flow inside an aneurysm artery but also for investigating the mechanical behavior of the blood flow in different arterial diseases, such as atherosclerosis.

scholarly journals Fish larvae exploit edge vortices along their dorsal and ventral fin folds to propel themselves

2016 ◽  
Vol 13 (116) ◽  
pp. 20160068 ◽  
Author(s):  
Gen Li ◽  
Ulrike K. Müller ◽  
Johan L. van Leeuwen ◽  
Hao Liu
Keyword(s):  
Larval Fish ◽  
Fish Larvae ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bony Fish ◽  
The Body ◽  
Functional Explanation ◽  
Image Velocimetry ◽  
Median Fins

Larvae of bony fish swim in the intermediate Reynolds number ( Re ) regime, using body- and caudal-fin undulation to propel themselves. They share a median fin fold that transforms into separate median fins as they grow into juveniles. The fin fold was suggested to be an adaption for locomotion in the intermediate Reynolds regime, but its fluid-dynamic role is still enigmatic. Using three-dimensional fluid-dynamic computations, we quantified the swimming trajectory from body-shape changes during cyclic swimming of larval fish. We predicted unsteady vortices around the upper and lower edges of the fin fold, and identified similar vortices around real larvae with particle image velocimetry. We show that thrust contributions on the body peak adjacent to the upper and lower edges of the fin fold where large left–right pressure differences occur in concert with the periodical generation and shedding of edge vortices. The fin fold enhances effective flow separation and drag-based thrust. Along the body, net thrust is generated in multiple zones posterior to the centre of mass. Counterfactual simulations exploring the effect of having a fin fold across a range of Reynolds numbers show that the fin fold helps larvae achieve high swimming speeds, yet requires high power. We conclude that propulsion in larval fish partly relies on unsteady high-intensity vortices along the upper and lower edges of the fin fold, providing a functional explanation for the omnipresence of the fin fold in bony-fish larvae.

Experimental Investigation of Effect of Tip Coolant Ejection on Internal Flow Characteristics Within a Realistic Blade Coolant Channel

2013 ◽  
Author(s):  
Jian Pu ◽  
Zhaoqing Ke ◽  
Jianhua Wang ◽  
Lei Wang ◽  
Hongde You
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Ratio ◽  
Lp Turbine ◽  
Mass Flow Ratio

This paper presents an experimental investigation on the characteristics of the fluid flow within an entire coolant channel of a low pressure (LP) turbine blade. The serpentine channel, which keeps realistic blade geometry, consists of three passes connected by a 180° sharp bend and a semi-round bend, 2 tip exits and 25 trailing edge exits. The mean velocity fields within several typical cross sections were captured using a particle image velocimetry (PIV) system. Pressure and flow rate at each exit were determined through the measurements of local static pressure and volume flow rate. To optimize the design of LP turbine blade coolant channels, the effect of tip ejection ratio (ER) from 180° sharp bend on the flow characteristics in the coolant channel were experimentally investigated at a series of inlet Reynolds numbers from 25,000 to 50,000. A complex flow pattern, which is different from the previous investigations conducted by a simplified square or rectangular two-pass U-channel, is exhibited from the PIV results. This experimental investigation indicated that: a) in the main flow direction, the regions of separation bubble and flow impingement increase in size with a decrease of the ER; b) the shape, intensity and position of the secondary vortices are changed by the ER; c) the mass flow ratio of each exit to inlet is not sensitive to the inlet Reynolds number; d) the increase of the ER reduces the mass flow ratio through each trailing edge exit to the extent of about 23–28% of the ER = 0 reference under the condition that the tip exit located at 180° bend is full open; e) the pressure drop through the entire coolant channel decreases with an increase in the ER and inlet Reynolds number, and a reduction about 35–40% of the non-dimensional pressure drop is observed at different inlet Reynolds numbers, under the condition that the tip exit located at 180° bend is full open.

Numerical Simulation for Flow over Two Circular Cylinders in Micro Channel with Lattice Boltzmann Method

2014 ◽  
Vol 670-671 ◽  
pp. 747-750
Author(s):  
Zhi Jun Gong ◽  
Jiao Yang ◽  
Wen Fei Wu
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Recirculation Zone ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Micro Channel ◽  
Zone Length ◽  
Spacing Ratio ◽  
Boltzmann Method

For indepth study on flow characteristics for fluid bypass obstacles in micro-channel, the Lattice Boltzmann Method (LBM) was used to simulate fluid flow over two circular cylinders in side-by-side arrangement of a micro-channel. The velocity distribution and recirculation zone length under different Reynolds numbers (Re = 0~100) and different spacing ratio (H/D= 0~2.0) were obtained. The results show that the pattern of flow and the size of recirculation zone in the micro-channel depend on the combined effect of Re and H/D.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

Numerical Simulation on Heat Transfer and Fluid Flow Characteristics of Arrays With Nonuniform Plate Length Positioned Obliquely to the Flow Direction

1998 ◽  
Vol 120 (4) ◽  
pp. 991-998 ◽  
Author(s):  
L. B. Wang ◽  
G. D. Jiang ◽  
W. Q. Tao ◽  
H. Ozoe
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Numerical Results ◽  
The Body ◽  
Number Range ◽  
Plate Length ◽  
Nonuniform Plate ◽  
Short Plate

The periodically fully developed laminar heat transfer and pressure drop of arrays with nonuniform plate length aligned at an angle (25 deg) to air direction have been investigated by numerical analysis in the Reynolds number range of 50–1700. The body-fitted coordinate system generated by the multisurface method was adopted to retain the corresponding periodic relation of the lines in physical and computational domains. The computations were carried out just in one cycle. Numerical results show that both the heat transfer and pressure drop increase with the increase in the length ratio of the long plate to the short plate, and decrease with the decrease in the ratio of transverse pitch to the longitudinal pitch. The numerical results exhibit good agreement with available experimental data.

scholarly journals Plasma Flows in Solar Filaments as Electromagnetically Driven Vortical Flows

Physics ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1046-1050
Author(s):  
Yuri E. Litvinenko
Keyword(s):  
Reynolds Numbers ◽  
Flow Speed ◽  
The Body ◽  
Exact Analytical Solutions ◽  
Electric And Magnetic Fields ◽  
Solar Filaments ◽  
Archimedean Force ◽  
Streaming Flows ◽  
Plasma Flow Speed ◽  
Scaling Arguments

Electromagnetic expulsion acts on a body suspended in a conducting fluid or plasma, which is subject to the influence of electric and magnetic fields. Physically, the effect is a magnetohydrodynamic analogue of the buoyancy (Archimedean) force, which is caused by the nonequal electric conductivities inside and outside the body. It is suggested that electromagnetic expulsion can drive the observed plasma counter-streaming flows in solar filaments. Exact analytical solutions and scaling arguments for a characteristic plasma flow speed are reviewed, and their applicability in the limit of large magnetic Reynolds numbers, relevant in the solar corona, is discussed.

Convective micromixers — design and industrial applications

2008 ◽  
Vol 222 (5) ◽  
pp. 807-816 ◽  
Author(s):  
N Kockmann
Keyword(s):  
Transient Flow ◽  
Phase Particle ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Industrial Applications ◽  
Particle Generation ◽  
Vitamin E Acetate ◽  
Mass Flowrate ◽  
High Reynolds ◽  
20 Nm

Convective static micromixers operate with high Reynolds numbers ( Re from 100 to 1000) in relatively large microchannels (100–1000 μm) for high flowrates and low risk of fouling and blocking. Typical flow characteristics of symmetrical mixing in T-shaped micromixers are presented with transient flow for Re number larger than 240. The simulation results are assisted by experimental data. Parallel mixing elements increase the mass flowrate up to 25 kg/h with 100 kPa pressure loss. The typical flow characteristics are described, which are essential for successful mixing devices. Three dimensionless parameters are introduced to describe the mixing performance and effectiveness of such devices. Particle generation are critical in microchannels due to fouling issues. The gas phase particle generation from homogeneous condensation of vitamin E acetate is described, reaching to particle diameters of 20 nm from temporal temperature gradients of about 1.6×106 K/s. In liquid phase, the reactive precipitation of BaSO4 is investigated, leading to particle diameters below 100 nm.

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