Experimental studies of strongly stratified flow past three-dimensional orography

1999 ◽  
Vol 390 ◽  
pp. 223-249 ◽  
Author(s):  
S. B. VOSPER ◽  
I. P. CASTRO ◽  
W. H. SNYDER ◽  
S. D. MOBBS
Keyword(s):  
Flow Visualization ◽  
Froude Number ◽  
Vortex Shedding ◽  
Wave Amplitude ◽  
Wave Train ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Stratified Flow ◽  
Finite Depth ◽  
Buoyancy Frequency

Stably stratified flows past three-dimensional orography have been investigated using a stratified towing tank. Flows past idealized axisymmetric orography in which the Froude number, Fh=U/Nh (where U is the towing speed, N is the buoyancy frequency and h is the height of the obstacle) is less than unity have been studied. The orography considered consists of two sizes of hemisphere and two cones of different slope. For all the obstacles measurements show that as Fh decreases, the drag coefficient increases, reaching between 2.8 and 5.4 times the value in neutral flow (depending on obstacle shape) for Fh[les ]0.25. Local maxima and minima in the drag also occur. These are due to the finite depth of the tank and can be explained by linear gravity-wave theory. Flow visualization reveals a lee wave train downstream in which the wave amplitude is O(Fhh), the smallest wave amplitude occurring for the steepest cone. Measurements show that for all the obstacles, the dividing-streamline height, zs, is described reasonably well by the formula zs/h=1−Fh. Flow visualization and acoustic Doppler velocimeter measurements in the wake of the obstacles show that vortex shedding occurs when Fh[les ]0.4 and that the period of the vortex shedding is independent of height. Based on velocity measurements in the wake of both sizes of hemisphere (plus two additional smaller hemispheres), it is shown that a blockage-corrected Strouhal number, S2c =fL2/Uc, collapses onto a single curve when plotted against the effective Froude number, Fhc=Uc/Nh. Here, Uc is the blockage-corrected free-stream speed based on mass-flux considerations, f is the vortex shedding frequency and L2 is the obstacle width at a height zs/2. Collapse of the data is also obtained for the two different shapes of cone and for additional measurements made in the wake of triangular and rectangular at plates. Indeed, the values of S2c for all these obstacles are similar and this suggests that despite the fact that the obstacle widths vary with height, a single length scale determines the vortex-street dynamics. Experiments conducted using a splitter plate indicate that the shedding mechanism provides a major contribution to the total drag (∼25%). The addition of an upstream pointing ‘verge region’ to a hemisphere is also shown to increase the drag significantly in strongly stratified flow. Possible mechanisms for this are discussed.

Three-dimensional problem of exponentially stratified flow over bottom roughness in the case of finite depth

1990 ◽  
Vol 25 (3) ◽  
pp. 415-423
Author(s):  
K. A. Bezhanov ◽  
P. G. Zaets ◽  
A. T. Onufriev ◽  
A. M. Ter-Krikorov
Keyword(s):  
Three Dimensional ◽  
Stratified Flow ◽  
Finite Depth ◽  
Dimensional Problem

scholarly journals On the Rapid Spectral Evolution of Steep Wave Groups with Directional Spreading at Intermediate Depths

2020 ◽  
Author(s):  
Dylan Barratt ◽  
Harry B. Bingham ◽  
Paul H. Taylor ◽  
Ton S. van den Bremer ◽  
Thomas A. A. Adcock
Keyword(s):  
Wave Train ◽  
Three Dimensional ◽  
Finite Depth ◽  
Wave Group ◽  
Spectral Evolution ◽  
Wave Groups ◽  
Return Current ◽  
Resonant Interactions ◽  
Energy Transfers ◽  
Steep Wave

<p>We have performed numerical simulations of steep three-dimensional wave groups, formed by dispersive focusing, using the fully-nonlinear potential flow solver <em>OceanWave3D</em>. We find that third-order resonant interactions result in directional energy transfers to higher-wavenumber components, forming steep wave groups with augmented kinematics and a prolonged lifespan. If the wave group is initially narrow banded, <em>quasi-degenerate interactions</em> resembling the instability band of a regular wave train arise, characterised by unidirectional energy transfers and energy transfers along the resonance angle, ±35.26°, of the Phillips ‘figure-of-eight’ loop. Spectral broadening due to the quasi-degenerate interactions eventually facilitates <em>non-degenerate interactions</em>, which dominate the spectral evolution of the wave group after focus. The non-degenerate interactions manifest primarily as a high-wavenumber sidelobe, which forms at an angle of ±55° to the spectral peak. We consider finite-depth effects in the range of deep to intermediate waters (5.592 ≥ <em>k<sub>p</sub>d</em> ≥ 1.363), based on the characteristic wavenumber (<em>k<sub>p</sub></em>) and the domain depth (<em>d</em>), and find that all forms of spectral evolution are suppressed by depth. However, the quasi-degenerate interactions exhibit a greater sensitivity to depth, suggesting suppression of the modulation instability by the return current, consistent with previous studies. We also observe sensitivity to depth for <em>k<sub>p</sub>d</em> values commonly considered "deep", indicating that the length scales of the wave group and return current may be better indicators of dimensionless depth than the length scale of any individual wave component. The non-degenerate interactions appear to be depth resilient with persistent evidence of a ±55° spectral sidelobe at a depth of <em>k<sub>p</sub>d</em> =1.363. Although the quasi-degenerate interactions are significantly suppressed by depth, the interactions do not entirely disappear for <em>k<sub>p</sub>d</em> =1.363 and show signs of biasing towards oblique, rather than unidirectional, wave components at intermediate depths. The contraction of the wavenumber spectrum in the <em>k<sub>y</sub></em>-direction has also proved to be resilient to depth, suggesting that lateral expansion of the wave group and the "wall of water" effect of Gibbs & Taylor (2005) may persist at intermediate depths.</p>

scholarly journals Three-dimensional numerical study of submerged spatial hydraulic jumps

2020 ◽  
Vol 68 (3) ◽  
pp. 211-222
Author(s):  
Ahmed S. Foda ◽  
Yehya E. Imam ◽  
Abd Allah S. Bazaraa ◽  
Emad H. Imam
Keyword(s):  
Numerical Model ◽  
Froude Number ◽  
Numerical Study ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Expansion Ratio ◽  
Hydraulic Jumps ◽  
Aspect Ratios ◽  
Jump Length ◽  
Oscillation Frequencies

AbstractA three-dimensional numerical model was applied to simulate submerged spatial hydraulic jumps (SSHJ) downstream of a symmetric vent that discharges into a wider channel. Simulations were carried out for different aspect ratios of the vent, expansion ratios of vent width to downstream channel width, tailwater depth, and inlet Froude number. Depending on these factors, simulations indicated the formation of steady asymmetric SSHJ, oscillatory asymmetric SSHJ, and steady symmetric SSHJ, consistent with results of previous experimental studies. The model reproduced observed depth downstream of vent, jump length, and velocity profiles along channel centerline for steady symmetric SSHJ. For oscillatory asymmetric SSHJ, simulated oscillation frequencies had Strouhal numbers that varied with expansion ratio and ranged between 0.003 and 0.015. With piers downstream of the vent, oscillatory SSHJ continued to exhibit jet deflections when pier length was relatively short ( ≲ 0.2 of jump length) but became steady asymmetric for longer piers.

An Experimental Study of Flow Past a Dual Step Cylinder

2010 ◽  
Author(s):  
Chris R. Morton ◽  
Serhiy Yarusevych
Keyword(s):  
Flow Visualization ◽  
Vortex Shedding ◽  
Large Diameter ◽  
Three Dimensional ◽  
Small Diameter ◽  
Single Vortex ◽  
Aspect Ratios ◽  
Flow Past ◽  
Large Cylinder ◽  
Small Cylinder

Flow past a dual step cylinder has been investigated using experimental flow visualization methods. The dual step cylinder model is comprised of a small diameter cylinder (d) and a large diameter cylinder (D) mounted at the mid-span of the small cylinder. The experiments have been performed for ReD = 1050, D/d = 2, and a range of large cylinder aspect ratios (L/D). The focus of the study is on vortex shedding and vortex interactions occurring in the large and small cylinder wakes. A flow visualization study completed using hydrogen bubble technique and planar laser induced fluorescence has shown that the flow development is highly dependent on the aspect ratio of the large cylinder, L/D. The results identify four distinct flow regimes: (i) for L/D ≥ 17, three vortex shedding cells form in the wake of the large cylinder, one central cell and two cells of lower frequency extending over about 4.5D from the large cylinder ends, (ii) for 7 < L/D ≤ 14, a single vortex shedding cell forms in the wake of the large cylinder, whose shedding frequency decreases with decreasing L/D, (iii) for 2 ≤ L/D ≤ 7, vortex shedding in the wake of the large cylinder is highly three-dimensional, such that each vortex deforms while it is shed into the wake, (iv) for 0.2 ≤ L/D ≤ 1, only small cylinder vortices are shed in the wake and often form vortex connections across the wake of the large cylinder.

Experimental Studies of Sedimentation Basin Dynamics

1977 ◽  
Vol 12 (1) ◽  
pp. 77-90
Author(s):  
J.F. Cordoba-Molina ◽  
P.L. Silveston ◽  
R. R. Hudgins
Keyword(s):  
Dynamic Response ◽  
Froude Number ◽  
Flow Model ◽  
Experimental Studies ◽  
Densimetric Froude Number ◽  
Number Range ◽  
The Real ◽  
Highly Correlated ◽  
Sedimentation Basins ◽  
Simple Flow

Abstract A simple Flow Model is proposed to describe the dynamic response of sedimentation basins. The response predicted by this model is linear as opposed to the real response of the basin which is nonlinear. However, the real response of the basin is highly correlated with its densimetric Froude number, and as a consequence our linear model effectively predicts the response of the basin in a restricted densimetric Froude Number range. Our experiments show that the response of the basin becomes more sluggish and erratic as the densimetric Froude number decreases.

Visualizing Fluid Flows With X-Rays

2007 ◽  
Author(s):  
Theodore J. Heindel ◽  
Terrence C. Jensen ◽  
Joseph N. Gray
Keyword(s):  
Computed Tomography ◽  
Flow Visualization ◽  
Three Dimensional ◽  
Fluid Flows ◽  
X Rays ◽  
Radiographic Images ◽  
Optical Access ◽  
X Ray ◽  
X Ray Computed ◽  
Density Map

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will be presented. When two X-ray sources and detectors simultaneously acquire images of the same process or object from different orientations, stereographic imaging can be completed; this type of imaging will be demonstrated by trickling water through packed columns and by absorbing water in a porous medium. Finally, local time-averaged phase distributions can be determined from X-ray computed tomography (CT) imaging, and this will be shown by comparing CT images from two different gas-liquid sparged columns.

scholarly journals Targeting hepatocyte growth factor in epithelial–stromal interactions in an in vitro experimental model of human periodontitis

Odontology ◽  
2021 ◽  
Author(s):  
Yoko Yamaguchi ◽  
Akira Saito ◽  
Masafumi Horie ◽  
Akira Aoki ◽  
Patrick Micke ◽  
...  
Keyword(s):  
Growth Factor ◽  
Hepatocyte Growth Factor ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Collagen Gel ◽  
Neutralizing Antibody ◽  
Chronic Inflammatory Disease ◽  
Collagen Degradation ◽  
Hepatocyte Growth

AbstractPeriodontitis is a chronic inflammatory disease leading to progressive connective tissue degradation and loss of the tooth-supporting bone. Clinical and experimental studies suggest that hepatocyte growth factor (HGF) is involved in the dysregulated fibroblast–epithelial cell interactions in periodontitis. The aim of this study was to explore effects of HGF to impact fibroblast-induced collagen degradation. A patient-derived experimental cell culture model of periodontitis was applied. Primary human epithelial cells and fibroblasts isolated from periodontitis-affected gingiva were co-cultured in a three-dimensional collagen gel. The effects of HGF neutralizing antibody on collagen gel degradation were tested and transcriptome analyses were performed. HGF neutralizing antibody attenuated collagen degradation and elicited expression changes of genes related to extracellular matrix (ECM) and cell adhesion, indicating that HGF signaling inhibition leads to extensive impact on cell–cell and cell–ECM interactions. Our study highlights a potential role of HGF in periodontitis. Antagonizing HGF signaling by a neutralizing antibody may represent a novel approach for periodontitis treatment.

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