scholarly journals Effects of coral colony morphology on turbulent flow dynamics

2019 ◽  
Author(s):  
Md Monir Hossain ◽  
Anne E. Staples
Keyword(s):  
Turbulent Flow ◽  
Three Dimensional ◽  
Velocity Profiles ◽  
High Flow ◽  
Flow Dynamics ◽  
Immersed Boundary ◽  
Mean Velocity ◽  
Local Flow ◽  
The Mean ◽  
Mixing And Transport

AbstractLocal flow dynamics play a central role in physiological processes like respiration and nutrient uptake in coral reefs. Despite the importance of corals as hosts to a quarter of all marine life, and the pervasive threats currently facing corals, little is known about the detailed hydrodynamics of branching coral colonies. Here, in order to investigate the effects of the colony branch density and surface roughness on the local flow field, three-dimensional simulations were performed using immersed boundary, large-eddy simulations for four different colony geometries under low and high unidirectional oncoming flow conditions. The first two colonies were from the Pocillopora genus, one with a densely branched geometry, and one with a comparatively loosely branched geometry. The second pair of colony geometries were derived from a scan of a single Montipora capitata colony, one with the verrucae covering the surface intact, and one with the verrucae removed. We found that the mean velocity profiles in the densely branched colony changed substantially in the middle of the colony, becoming significantly reduced at middle heights where flow penetration was poor, while the mean velocity profiles in the loosely branched colony remained similar in character from the front to the back of the colony, with no middle-range velocity deficit appearing at the center of the colony. When comparing the turbulent flow statistics at the surface of the rough and smooth M. capitata colonies, we found higher Reynolds stress components for the smooth colony, indicating higher rates of mixing and transport compared to the rough colony, which must sacrifice mixing and transport efficiency in order to maintain its surface integrity in its natural high-flow environment. These results suggest that the densely branched, roughly patterned corals found in high flow areas may be more resistant not only to breakage, but also to flow penetration.

Experimental Study of the Flow in a Simulated Hard Disk Drive

2006 ◽  
Vol 128 (5) ◽  
pp. 1090-1100 ◽  
Author(s):  
Charlotte Barbier ◽  
Joseph A. C. Humphrey ◽  
Eric Maslen
Keyword(s):  
Hard Disk Drive ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Hard Disk ◽  
Disk Drive ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Local Flow ◽  
The Mean ◽  
Fundamental Value

Instantaneous circumferential and radial velocity components of the air flowing past a symmetrical pair of suspension/slider-units (SSUs) attached to an E-Block/arm were measured in a specially designed corotating disk apparatus simulating a hard disk drive (HDD) using the particle image velocimetry technique. The geometrical dimensions of the components in the apparatus test section were scaled up by a factor of two, approximately, relative to those of a nominal 312 inch HDD. Most of the measurements were obtained on the interdisk midplane for two angular orientations of the arm/SSUs: (a) One with the tip of the SSUs near the hub supporting the disks; (b) another with the tip of the SSUs near the rims of the disks. Data obtained for disk rotational speeds ranging from 250 to 3000rpm (corresponding to 1250 to 15,000rpm, approximately, in a 312 inch HDD) were post-processed to yield mean and rms values of the two velocity components and of the associated shear stress, the mean axial vorticity, and the turbulence intensity (based on the two velocity components). At the locations investigated near the arm/SSUs, and for disk rotational speeds larger than 1500rpm, the mean velocity components are found to be asymptotically independent of disk speed of rotation but their rms values appear to still be changing. At two locations 90 and 29deg, respectively, upstream of the arm/SSUs, the flow approaching this obstruction displays features that can be attributed to the three-dimensional wake generated by the obstruction. Also, between these two locations and depending on the angular orientation of the arm/SSUs, the effect of the obstruction is to induce a three-dimensional region of flow reversal adjacent to the hub. Notwithstanding, the characteristics of the flow immediately upstream and downstream of the arm/SSUs appear to be determined by local flow-structure interactions. Aside from their intrinsic fundamental value, the data serve to guide and test the development of turbulence models and numerical calculation procedures for predicting this complex class of confined rotating flows, and to inform the improved design of HDDs.

Another look at unidirectional turbulent flow

1995 ◽  
Vol 287 ◽  
pp. 75-92 ◽  
Author(s):  
A. J. Reynolds ◽  
K. Wieghardt
Keyword(s):  
Variational Principle ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Core Region ◽  
Flat Channel ◽  
Mean Velocity ◽  
Channel One ◽  
The Core ◽  
The Mean

Here we consider the mean velocity profile in the core region of a unidirectional turbulent flow, that is, a flow in which the turbulent motion is superposed upon parallel time-averaged streamlines. A kinematical variational principle, originally developed for three-dimensional free-turbulent motions, is shown to be applicable to significant parts of the velocity profiles for flows of both Couette and Poiseuille types. In addition to pure plane Couette and pure plane Poiseuille flows, the motions considered include a variety of admixtures produced by blowing through a wide flat channel one of whose walls comprises a belt which moves either in the direction of the blowing or counter to it.

Turbulent Flow Through a Ducted Elbow and Plugged Tee Geometry: An Experimental and Numerical Study

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Andrew M. Bluestein ◽  
Ravon Venters ◽  
Douglas Bohl ◽  
Brian T. Helenbrook ◽  
Goodarz Ahmadi
Keyword(s):  
Turbulent Flow ◽  
Pressure Loss ◽  
Numerical Study ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Flow Features ◽  
Reynolds Number Effects ◽  
The Mean ◽  
Rans Simulations

An experimental and computational comparison of the turbulent flow field for a sharp 90 deg elbow and plugged tee junction is presented. These are commonly used industrial geometries with the tee often retrofitted by plugging the straight exit to create an elbow. Mean and fluctuating velocities along the midplane were measured via two-dimensional (2D) particle image velocimetry (PIV), and the results were compared with the predictions of Reynolds-averaged Navier–Stokes (RANS) simulations for Reynolds numbers of 11,500 and 115,000. Major flow features of the elbow and plugged tee were compared using the mean velocity contours. Geometry effects and Reynolds number effects were studied by examining the mean and root-mean-square (RMS) fluctuating velocity profiles at six positions. Finally, the asymmetry of the flow as measured by the position of the centroid of the volumetric flux and pressure loss data were examined to quantify the streamwise evolution of the flow in the respective geometries. It was found that in both geometries there was a large recirculation zone in the downstream leg but the RANS simulations predicted an overly long recirculation which led to significantly different mean and fluctuating velocities in that region when compared to the experiments. Comparison of velocity profiles showed that both experiments and numerics agree in the fact that the turbulence intensities were greater at higher Re downstream of the vertical leg. Finally, it was shown that the plugged tee recovered its symmetry more rapidly and created less pressure loss than the elbow.

Effects of Upstream Disturbances on the Spreading of Large Fluid-Amplifier-Type Jets

1971 ◽  
Vol 93 (1) ◽  
pp. 53-60
Author(s):  
R. W. Gray ◽  
J. L. Shearer
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Jet Flow ◽  
Velocity Profiles ◽  
Mean Velocity ◽  
Disturbance Intensity ◽  
Flow Disturbances ◽  
Jet Nozzle ◽  
The Mean ◽  
Constant Maximum

Flow disturbances were introduced upstream of a rectangular nozzle and spreading jet confined by top and bottom plates to determine the effect on the velocity profiles. The mean velocity and turbulence distributions in the symmetrical mixing regions near a given nozzle are presented for several upstream disturbance intensity levels and several jet nozzle exit velocities. For the essentially two-dimensional jet flow from a high aspect ratio nozzle the results at several upstream disturbance intensity levels revealed the mean velocity distribution to be self-preserving near the nozzle. Over a large range of upstream disturbance intensity inputs the location of the virtual origin for each mixing region changed significantly while the mixing regions exhibited a constant maximum dimensionless spread rate. Other results for the essentially three-dimensional jet flow from a low aspect ratio nozzle did not show self-preservation in the mixing regions and furthermore revealed extraordinary changes in the velocity profiles.

scholarly journals Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1718
Author(s):  
Hasan Zobeyer ◽  
Abul B. M. Baki ◽  
Saika Nowshin Nowrin
Keyword(s):  
Turbulent Flow ◽  
Open Channel ◽  
Recirculation Zone ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Recirculation ◽  
Tandem Cylinders ◽  
Flow Development ◽  
The Mean ◽  
Recirculation Length

The flow hydrodynamics around a single cylinder differ significantly from the flow fields around two cylinders in a tandem or side-by-side arrangement. In this study, the experimental results on the mean and turbulence characteristics of flow generated by a pair of cylinders placed in tandem in an open-channel flume are presented. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. This study investigated the effect of cylinder spacing at 3D, 6D, and 9D (center to center) distances on the mean and turbulent flow profiles and the distribution of near-bed shear stress behind the tandem cylinders in the plane of symmetry, where D is the cylinder diameter. The results revealed that the downstream cylinder influenced the flow development between cylinders (i.e., midstream) with 3D, 6D, and 9D spacing. However, the downstream cylinder controlled the flow recirculation length midstream for the 3D distance and showed zero interruption in the 6D and 9D distances. The peak of the turbulent metrics generally occurred near the end of the recirculation zone in all scenarios.

Experimental investigation on the momentumless wake using trailing edge blowing

2008 ◽  
Vol 222 (8) ◽  
pp. 1477-1486 ◽  
Author(s):  
Y Wu ◽  
X Zhu ◽  
Z Du
Keyword(s):  
Three Dimensional ◽  
Velocity Profiles ◽  
Axial Fan ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Velocity Spectra ◽  
Momentumless Wake ◽  
Wake Characteristics

A developed plate stator model with and without trailing edge blowing (TEB) is studied using experimental methods. Wake characteristics of flow over the stator in the three-dimensional wake regimes are studied using hot-wire anemometry (HWA) and particle image velocimetry (PIV) techniques. First, the mean velocity profiles have been measured in the wake of the stator using HWA. Four wake characteristics have been obtained through momentum thickness judgments: pure wake, weak wake, momentumless wake, and jet. These velocity profiles show some differences in momentum deficit for the four cases. Then, the velocity spectra of the pure wake and momentumless wake obtained through the HWA measurements showed that TEB can eliminate the shedding vortex of the stator. Characteristic length scales based on the wake turbulent intensity profiles showed that the momentumless wake can reduce the wake width and depth. PIV measurement is carried out to measure the flow field of the four wakes. Finally, the application of TEB approaching momentumless wake status is used on an industrial ventilation low-pressure axial fan to assess noise reduction. The results show that TEB can make the outlet of the stator uniform, reduce velocity fluctuation, destroy the vorticity structure downstream of the stator, and reduce interaction noise level of the stator and rotor.

On Turbulent Flow Between Parallel Plates

1953 ◽  
Vol 20 (1) ◽  
pp. 109-114
Author(s):  
S. I. Pai
Keyword(s):  
Turbulent Flow ◽  
Velocity Distribution ◽  
Poiseuille Flow ◽  
The Other ◽  
Turbulent Velocity ◽  
Parallel Plates ◽  
Mean Velocity ◽  
Reynolds Equations ◽  
Mean Pressure ◽  
The Mean

Abstract The Reynolds equations of motion of turbulent flow of incompressible fluid have been studied for turbulent flow between parallel plates. The number of these equations is finally reduced to two. One of these consists of mean velocity and correlation between transverse and longitudinal turbulent-velocity fluctuations u 1 ′ u 2 ′ ¯ only. The other consists of the mean pressure and transverse turbulent-velocity intensity. Some conclusions about the mean pressure distribution and turbulent fluctuations are drawn. These equations are applied to two special cases: One is Poiseuille flow in which both plates are at rest and the other is Couette flow in which one plate is at rest and the other is moving with constant velocity. The mean velocity distribution and the correlation u 1 ′ u 2 ′ ¯ can be expressed in a form of polynomial of the co-ordinate in the direction perpendicular to the plates, with the ratio of shearing stress on the plate to that of the corresponding laminar flow of the same maximum velocity as a parameter. These expressions hold true all the way across the plates, i.e., both the turbulent region and viscous layer including the laminar sublayer. These expressions for Poiseuille flow have been checked with experimental data of Laufer fairly well. It also shows that the logarithmic mean velocity distribution is not a rigorous solution of Reynolds equations.

ANCD thrombectomy device: in vitro evaluation

2019 ◽  
Vol 12 (1) ◽  
pp. 77-81 ◽  
Author(s):  
Sonia Sanchez ◽  
Ignacio Cortiñas ◽  
Helena Villanova ◽  
Anna Rios ◽  
Iñaki Galve ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Treatment Strategies ◽  
Local Flow ◽  
Guide Catheter ◽  
First Pass ◽  
Thrombectomy Device ◽  
The Mean ◽  
Three Dimensional Models ◽  
Number Of Passes

IntroductionEndovascular treatment of stroke, although highly effective, may fail to reach complete recanalization in around 20% of cases. The Advanced Thrombectomy System (ANCD) is a novel stroke thrombectomy device designed to reduce clot fragmentation and facilitate retrieval by inducing local flow arrest and allowing distal aspiration in combination with a stent retriever. We aimed to assess the preclinical efficacy of ANCD.MethodsSoft red blood cell (RBC)-rich (n=20/group) and sticky fibrin-rich (n=30/group) clots were used to create middle cerebral artery (MCA) occlusions in two vascular phantoms. Three different treatment strategies were tested: (1) balloon guide catheter + Solitaire (BGC+SR); (2) distal access catheter + SR (DAC+SR); and (3) ANCD+SR, until complete recanalization was achieved or to a maximum of three passes. The recanalization rate was determined after each pass.ResultsAfter one pass, ANCD+SR resulted in an increased recanalization rate (94%) for all clots together compared with BGC+SR (66%; p<0.01) or DAC+SR (80%; p=0.04). After the final pass the recanalization rate increased in all three groups but remained higher with ANCD+SR (100%) than with BGC+SR (74%; p<0.01) or DAC+SR (90%; p=0.02). The mean number of passes was lower with ANCD+SR (1.06) than with BGC+SR (1.46) or DAC+SR (1.25) (p=0.01). A logistic regression model adjusted for treatment arm, clot type, and model used showed that both RBC-rich clots (OR 8.1, 95% CI 1.6 to 13.5) and ANCD+SR (OR 3.9, 95% CI 1.01 to 15.8) were independent predictors of first-pass recanalization.ConclusionIn in vitro three-dimensional models replicating MCA-M1 occlusion, ANCD+SR showed significantly better recanalization rates in fewer passes than other commonly used combinations of devices.

Three-Dimensional Hybrid Vortex-Immersed Boundary Method With Application to Passive Flow Control

2015 ◽  
Author(s):  
Chloé Mimeau ◽  
Iraj Mortazavi ◽  
Georges-Henri Cottet
Keyword(s):  
Immersed Boundary Method ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Flow Dynamics ◽  
Immersed Boundary ◽  
Bluff Bodies ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Model Complex ◽  
Penalization Technique

In this work, a hybrid particle-penalization technique is proposed to achieve accurate and efficient computations of 3D incompressible flows past bluff bodies. This immersed boundary approach indeed maintains the efficiency and the robustness of vortex methods and allows to easily model complex media, like solid-fluid-porous ones, without prescribing any boundary condition. In this paper, the method is applied to implement porous coatings on a hemisphere in order to passively control the flow dynamics.

Turbulent Vorticity Diffusion in the Stronger Wall Jet Managed by a Flat Plate Wing in the Outer Layer

2015 ◽  
Author(s):  
Takuma Katayama ◽  
Shinsuke Mochizuki
Keyword(s):  
Shear Stress ◽  
Flat Plate ◽  
Outer Layer ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Wall Jet ◽  
Mean Velocity ◽  
The Mean

The present experiment focuses on the vorticity diffusion in a stronger wall jet managed by a three-dimensional flat plate wing in the outer layer. Measurement of the fluctuating velocities and vorticity correlation has been carried out with 4-wire vorticity probe. The turbulent vorticity diffusion due to the large scale eddies in the outer layer is quantitatively examined by using the 4-wire vorticity probe. Quantitative relationship between vortex structure and Reynolds shear stress is revealed by means of directly measured experimental evidence which explains vorticity diffusion process and influence of the manipulating wing. It is expected that the three-dimensional outer layer manipulator contributes to keep convex profile of the mean velocity, namely, suppression of the turbulent diffusion and entrainment.

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