Measurements of High Velocity Gradient Flow Using Bubble Tracers in a Cavitation Tunnel

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Bu-Geun Paik ◽  
Kyung-Youl Kim ◽  
Jong-Woo Ahn
Keyword(s):  
Velocity Gradient ◽  
High Velocity ◽  
Reynolds Shear Stress ◽  
Reduction Rate ◽  
Gradient Flow ◽  
Solid Particles ◽  
Vortical Flow ◽  
Propeller Wake ◽  
Cavitation Tunnel ◽  
High Velocity Gradient

The objective of the present study is to investigate propeller wake using particle image velocimetry (PIV) technique with bubble type of tracers, naturally generated by the decrease in the static pressure in a cavitation tunnel. The bubble can be grown from the nuclei melted in the water tunnel and the size of bubbles is changed by varying the tunnel pressure. A series of experiments are conducted in the conditions of the uniform and high velocity gradient flows to find out the characteristics of bubble tracers and compared the measurement results using bubbles with those using solid particles. Bubbles showed good trace ability in the region of 15<ReS<75; however, some discrepancies showed at high velocity gradient region of ReS≈1000. The fitted vorticity reduction rate would give reference for the prediction in a real flow when bubble tracers are utilized in PIV measurements of a vortical flow. In addition, the characteristics of bubble slip velocity can provide information on the vortex core center and the reduction in the Reynolds shear stress caused by bubble’s deformability.

Heterogeneous fragmentation of metallic liquid microsheet with high velocity gradient

2016 ◽  
Vol 25 (1) ◽  
pp. 017102 ◽  
Author(s):  
An-Min He ◽  
Pei Wang ◽  
Jian-Li Shao
Keyword(s):  
Velocity Gradient ◽  
High Velocity ◽  
Metallic Liquid ◽  
High Velocity Gradient

Behaviour of a polymer chain with a high velocity gradient in an extensional hydrodynamic field

1991 ◽  
Vol 33 (8) ◽  
pp. 1555-1562
Author(s):  
Yu.Ya. Gotlib ◽  
Ye.A. Karpov
Keyword(s):  
Polymer Chain ◽  
Velocity Gradient ◽  
High Velocity ◽  
Hydrodynamic Field ◽  
High Velocity Gradient

What does the 2A Event observed in the oceanic crust actually represent?

2021 ◽  
Author(s):  
Richard Hobbs ◽  
Christine Peirce
Keyword(s):  
High Temperature ◽  
Transition Zone ◽  
Oceanic Crust ◽  
Velocity Gradient ◽  
High Velocity ◽  
Seismic Energy ◽  
Lower Velocity ◽  
Layer 2 ◽  
Refraction Data ◽  
High Velocity Gradient

&lt;p&gt;The transition zone between the more porous upper extrusive layer (2A) and the less porous lower dyke layer (2B) within the oceanic crust is characterised by a high velocity gradient based on inversion of controlled-source, long-offset refraction data. In these data the phase associated with this high velocity gradient, termed the 2A Event, has an anomalously high amplitude over a limited range of offsets and appears to form a triplication with refractions from layer 2A above and 2B below. These characteristics fit the accepted model that this event is a caustic or retrograde phase, generated by a distinct layer whose thickness and velocity gradient can be determined by ray-trace modelling. Hence, a velocity model for Layer 2 (derived from seismic data acquired near ODP 504B) consists of a ~500 m-thick 2A with a velocity gradient of ~1.0 s&lt;sup&gt;-1&lt;/sup&gt;; a ~200 m-thick transition zone with a high velocity gradient of ~4.0 s&lt;sup&gt;-1&lt;/sup&gt;; and a ~1300 m-thick 2B with a velocity gradient of ~0.3 s&lt;sup&gt;-1&lt;/sup&gt;. However, this model is at odds with observation of Layer 2 lithology obtained from coring and ophiolites where the 2A is composed of a mixture of higher velocity basalt flows and lower velocity pillow lavas and breccia, with the transition zone represented by an increasing number of dykes which eventually make up 100% of the section in layer 2B combined and the effects of high-temperature alteration. Starting with a simplified but plausible geologically-based model, we show that it is possible to synthetically generate the observed 2A Event, and gain insight into what controls its visibility and variability in refraction data. Our primary findings show that the 2A Event will only form and propagate in the base of layer 2A, above the level where the higher velocities dominate. We also show that the amplitude of the 2A Event is sensitive to the local velocity structure of the extrusive layer and is most visible when seismic energy is focused by a low velocity layer. Hence, we conclude that the 2A Event is not a simple caustic, as defined by geometrical optics, but instead caused by the incident seismic energy being briefly concentrated in a leaky waveguide close to, but above, the mean depth of the dykes and the onset of high temperature alteration.&lt;/p&gt;

scholarly journals Supernova 2010ev: A reddened high velocity gradient type Ia supernova

2016 ◽  
Vol 590 ◽  
pp. A5 ◽  
Author(s):  
Claudia P. Gutiérrez ◽  
Santiago González-Gaitán ◽  
Gastón Folatelli ◽  
Giuliano Pignata ◽  
Joseph P. Anderson ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
High Velocity ◽  
Type Ia Supernova ◽  
Type Ia ◽  
Gradient Type ◽  
High Velocity Gradient

scholarly journals Prediction of particles deposition in a dilute quasi-steady gravity current by Lagrangian markers: effect of shear-induced lift force

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ali Koohandaz ◽  
Ehsan Khavasi ◽  
Arameh Eyvazian ◽  
Hamid Yousefi
Keyword(s):  
Velocity Gradient ◽  
High Velocity ◽  
Lift Force ◽  
Particle Deposition ◽  
Gravity Current ◽  
Sediment Deposition ◽  
Steady Flows ◽  
Vortical Structures ◽  
Over Time ◽  
High Velocity Gradient

Abstract A gravity current in a channel at the presence of a triangular obstacle was investigated using LES simulation and the Eulerian approach. The Saffman–Mei equation was also applied to examine the effect of shear-induced lift force on particle deposition. To this end, particles were considered as Lagrangian markers and injected into gravity current. It is important to keep in mind that the interaction between the gravity current and particles was treated as a one-way coupling. The results show that shear-induced lift force prevents particles to deposit at the entrance of channel, where the velocity gradient is high. Furthermore, a reduction in the rate of sediment deposition can be seen again in the vicinity of obstacle due to high velocity gradient. The important result is that the shear-induced lift force has an important role in the cases with considerable velocity gradient in quasi-steady flows and this force can affect the pattern of sedimentation over time. Q criterion is utilized to depict the vortical structures of flow. Vortical structures with larger diameter, that indicate stronger vortexes, has been seen in various sections of channel, especially in the region near the obstacle due to the presence of obstacle.

scholarly journals Unusual Cause of Heart Failure in a Patient with Marfan Syndrome: A Late Complication of Bioprosthetic Valved Graft Replacement

2020 ◽  
Vol 47 (1) ◽  
pp. 38-40
Author(s):  
Prerna B. Bansal ◽  
Hari P. Chaliki ◽  
Kantha R. Kolla ◽  
Roger L. Click ◽  
Alberto Pochettino
Keyword(s):  
Marfan Syndrome ◽  
Velocity Gradient ◽  
High Velocity ◽  
Left Ventricular Outflow Tract ◽  
Aortic Surgery ◽  
Ventricular Outflow Tract ◽  
Left Ventricular ◽  
Outflow Tract ◽  
Left Ventricular Outflow ◽  
High Velocity Gradient

A high-velocity gradient across the left ventricular outflow tract is most often caused by aortic valve stenosis. We describe the unusual case of a high-velocity gradient caused by a kinked ascending aortic graft in a 69-year-old man who had Marfan syndrome. The patient had a history of ascending aortic aneurysm and had previously undergone replacement of the aortic root and ascending aorta with use of a bioprosthetic valved graft. The kinking was caused by dilation of the native aortic arch. The patient underwent successful hemi-arch replacement and repair of the kinked graft. Late complications and reoperation after proximal aortic surgery in patients with Marfan syndrome are rare, and a high-velocity left ventricular outflow tract gradient caused by the kinking of the aorta is unusual.

Closure to “Drag Forces in Velocity Gradient Flow”

1962 ◽  
Vol 88 (4) ◽  
pp. 229-230
Author(s):  
Frank D. Masch ◽  
Walter L. Moore
Keyword(s):  
Velocity Gradient ◽  
Gradient Flow ◽  
Drag Forces

Discussion of “Drag Forces in Velocity Gradient Flow”

1961 ◽  
Vol 87 (2) ◽  
pp. 181-183
Author(s):  
Donald Van Sickle
Keyword(s):  
Velocity Gradient ◽  
Gradient Flow ◽  
Drag Forces

Free Surface, Velocity Gradient Flow Past Hemisphere

1970 ◽  
Vol 96 (7) ◽  
pp. 1485-1502
Author(s):  
Gordon H. Flammer ◽  
J. Paul Tullis ◽  
Earl S. Mason
Keyword(s):  
Free Surface ◽  
Velocity Gradient ◽  
Gradient Flow ◽  
Surface Velocity ◽  
Free Surface Velocity ◽  
Flow Past

Simulation and Analysis of Flow Field Control in Bionic Jet Surface for Drag Reduction

2013 ◽  
Vol 461 ◽  
pp. 746-750
Author(s):  
Zhao Gang ◽  
Fang Li ◽  
Jun Wei Du ◽  
Muhammad Farid ◽  
Dong Yang Zang
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Drag Reduction ◽  
Velocity Gradient ◽  
Reverse Flow ◽  
Reduction Rate ◽  
Frictional Resistance ◽  
Longitudinal Direction ◽  
Bottom Layer ◽  
Control Behavior

Numerical simulation was used with SST turbulence model on the drag reduction characteristics of bionic jet surface, which clarified the reason that the bionic jet surface could reduce the frictional resistance and the control behavior to the flow field near the wall. Results show that when the area of the jet hole is constant, the higher the ratio of the length along the longitudinal direction of jet hole and that of jet surface is, the better the drag reduction effect is. With the jet speed and jet flux increasing, the drag reduction rate will increase gradually until the maximum of 35.97%. The frictional resistance of bionic jet surface will decrease by increasing the area of reverse flow and decreasing the velocity gradient of the wall; the control behavior of jet surface to boundary layer embodies the shear stress in the bottom of boundary layer caused by the reverse flow in the back flow surface is opposite to the main flow field direction when the shear flow near the wall converges the jet impedance, which causes the low speed reverse rotating vortex pair in the downstream of jet hole, the secondary vortex near the wall caused by the extent of reverse vortex towards the downstream can increase the boundary bottom layer thickness and decrease the velocity gradient and frictional resistance.

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