On the Stability of a Flow Between Two Vertical Planes Caused by Homogeneous Heat Source and Pressure Gradient

1995 ◽  
pp. 3-9
Author(s):  
Francesco Mollica
Keyword(s):  
Heat Source ◽  
Pressure Gradient ◽  
The Stability

Transition of streamwise streaks in zero-pressure-gradient boundary layers

2002 ◽  
Vol 472 ◽  
pp. 229-261 ◽  
Author(s):  
LUCA BRANDT ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
High Speed ◽  
Plate Boundary ◽  
Transition Process ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting ◽  
Streamwise Streaks ◽  
The Stability ◽  
Optimal Disturbances

A transition scenario initiated by streamwise low- and high-speed streaks in a flat-plate boundary layer is studied. In many shear flows, the perturbations that show the highest potential for transient energy amplification consist of streamwise-aligned vortices. Due to the lift-up mechanism these optimal disturbances lead to elongated streamwise streaks downstream, with significant spanwise modulation. In a previous investigation (Andersson et al. 2001), the stability of these streaks in a zero-pressure-gradient boundary layer was studied by means of Floquet theory and numerical simulations. The sinuous instability mode was found to be the most dangerous disturbance. We present here the first simulation of the breakdown to turbulence originating from the sinuous instability of streamwise streaks. The main structures observed during the transition process consist of elongated quasi-streamwise vortices located on the flanks of the low-speed streak. Vortices of alternating sign are overlapping in the streamwise direction in a staggered pattern. The present scenario is compared with transition initiated by Tollmien–Schlichting waves and their secondary instability and by-pass transition initiated by a pair of oblique waves. The relevance of this scenario to transition induced by free-stream turbulence is also discussed.

Modeling of External Pressure Gradient Influence on the Stability of Disturbances in the Boundary Layers of Compressed Gas

2013 ◽  
Vol 8 (4) ◽  
pp. 64-75
Author(s):  
Sergey Gaponov ◽  
Natalya Terekhova
Keyword(s):  
Mach Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Leading Edge ◽  
External Pressure ◽  
Transition To Turbulence ◽  
Compressed Gas ◽  
High Mach ◽  
The Stability ◽  
Very High

This work continues the research on modeling of passive methods of management of flow regimes in the boundary layers of compressed gas. Authors consider the influence of pressure gradient on the evolution of perturbations of different nature. For low Mach number M = 2 increase in pressure contributes to an earlier transition of laminar to turbulent flow, and, on the contrary, drop in the pressure leads to a prolongation of the transition to turbulence. For high Mach number M = 5.35 found that the acoustic disturbances exhibit a very high dependence on the sign and magnitude of the external gradient, with a favorable gradient of the critical Reynolds number becomes smaller than the vortex disturbances, and at worst – boundary layer is destabilized directly on the leading edge

On the stability of viscous flow in a curved channel

1958 ◽  
Vol 244 (1237) ◽  
pp. 186-198 ◽  
Keyword(s):  
Approximate Solution ◽  
Pressure Gradient ◽  
Viscous Flow ◽  
Close Agreement ◽  
Curved Channel ◽  
A Value ◽  
Concentric Cylinders ◽  
The Stability ◽  
Pattern Of Motion

In this paper the stability of viscous flow between two concentric cylinders due to a pressure gradient acting round the cylinders is considered when the spacing between the cylinders is small compared with their radii. Two methods of approximate solution are described, both of which show that instability first sets in when the parameter R √( d / R 1 ) attains a value of about 36 in close agreement with earlier results of Dean (1928). The pattern of motion which then sets in is of the familar cellular type but with a marked asymmetry.

scholarly journals Unsteady Seepage Behavior of an Earthfill Dam During Drought-Flood Cycles

Geosciences ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 17 ◽  
Author(s):  
Ziyang Li ◽  
Wei Ye ◽  
Miroslav Marence ◽  
Jeremy Bricker
Keyword(s):  
Pressure Gradient ◽  
Water Level ◽  
Pore Pressure ◽  
Internal Erosion ◽  
Reservoir Water ◽  
Reservoir Water Level ◽  
Upstream Slope ◽  
Earthfill Dams ◽  
The Stability ◽  
Pore Pressure Gradient

Climate change with extreme hydrological conditions, such as drought and flood, bring new challenges to seepage behavior and the stability of earthfill dams. Taking a drought-stricken earthfill dam of China as an example, the influence of drought-flood cycles on dam seepage behavior is analyzed. This paper includes a clay sample laboratory experiment and an unsteady finite element method seepage simulation of the mentioned dam. Results show that severe drought causes cracks on the surface of the clay soil sample. Long-term drought causes deeper cracks and induces a sharp increase of suction pressure, indicating that the cracks would become channels for rain infiltration into the dam during subsequent rainfall, increasing the potential for internal erosion and decreasing dam stability. Measures to prevent infiltration on the dam slope surface are investigated, for the prevention of deep crack formation during long lasting droughts. Unsteady seepage indicators including instantaneous phreatic lines, equipotential lines and pore pressure gradient in the dam, are calculated and analyzed under two assumed conditions with different reservoir water level fluctuations. Results show that when the water level changes rapidly, the phreatic line is curved and constantly changing. As water level rises, equipotential lines shift upstream, and the pore pressure gradient in the dam’s main body is larger than that of steady seepage. Furthermore, the faster the water level rises, the larger the pore pressure gradient is. This may cause internal erosion. Furthermore, the case of a cracked upstream slope is modelled via an equivalent permeability coefficient, which shows that the pore pressure gradient in the zone beneath the cracks increases by 5.9% at the maximum water level; this could exacerbate internal erosion. In addition, results are in agreement with prior literature that rapid drawdown of the reservoir water level is detrimental to the stability of the upstream slope based on embankment slope stability as calculated by the Simplified Bishop Method. It is concluded that fluctuations of reservoir water level should be strictly controlled during drought-flood cycles; both the drawdown rate and the fill rate must be regulated to avoid the internal erosion of earthfill dams.

Effect of pressure gradient in the connection region on the stability of the edge pedestal

2020 ◽  
Vol 60 (7) ◽  
pp. 076022
Author(s):  
S.K. Kim ◽  
S. Saarelma ◽  
Y.-S. Na ◽  
O. Kwon
Keyword(s):  
Pressure Gradient ◽  
Effect Of Pressure ◽  
The Stability

scholarly journals Stability of Sheet Flow of Water Beneath Temperate Glaciers and Implications for Glacier Surging

1982 ◽  
Vol 28 (99) ◽  
pp. 273-293 ◽  
Author(s):  
Joseph S. Walder
Keyword(s):  
Mathematical Model ◽  
Pressure Gradient ◽  
Heat Dissipation ◽  
Sheet Thickness ◽  
Sheet Flow ◽  
High Speeds ◽  
Effective Roughness ◽  
Viscous Heat ◽  
Surface Slopes ◽  
The Stability

AbstractA mathematical model is presented for the stability of sheet flow of water beneath a temperate glacier. Enhanced viscous heat dissipation in thick parts of the sheet tends to make sheet flow unstable, the instability increasing as sheet thickness and pressure gradient increase. However, incipient channels may be destroyed as the glacier slides over protuberances on its bed. Quasi-stable sheet flow may be possible for sheets up to several millimeters in thickness, especially beneath glaciers that have relatively gentle surface slopes and slide at moderate to high speeds. Such water sheets may somewhat reduce the effective roughness of glacier beds, but probably not enough to allow surge initiation. Furthermore, the presence of numerous water-filled cavities at the glacier bed will tend to reduce the sheet thickness and lessen the degree of “lubrication” of the glacier bed by the water sheet.

scholarly journals STABILITY OF A SAND BED UNDER BREAKING WAVES

1974 ◽  
Vol 1 (14) ◽  
pp. 45 ◽  
Author(s):  
Ole Secher Madsen
Keyword(s):  
Pressure Gradient ◽  
Surf Zone ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Light Weight ◽  
Loss Of Stability ◽  
Vertical Flow ◽  
Sufficient Magnitude ◽  
The Stability ◽  
Bed Material

The possible effect on the stability of a porous sand bed of the flow induced within the bed during the passage of near-breaking or breaking waves is considered. It is found that the horizontal flow rather than the vertical flow within the bed may affect its stability. An approximate analysis, used in geotechnical computations of slope stability, indicates that a momentary bed failure is likely to occur during the passage of the steep front slope of a near-breaking wave. Experimental results for the pressure gradient along the bottom under near-breaking waves are presented. These results indicate that the pressure gradient is indeed of sufficient magnitude to cause the momentary failure suggested by the theoretical analysis. The loss of stability of the bed material due to the flow induced within the bed itself may affect the amount of material set in motion during the passage of a near-breaking or breaking wave, in particular, in model tests employing light weight bed material. The failure mechanism considered here is also used as the basis for a hypothesis for the depth of disturbance of the bed in the surf zone. The flow induced in a porous bed is concluded to be an important mechanism which should be considered when dealing with the wave-sediment interaction in the surf zone.

Study on Vinyl Ester Based Structural Anchor Adhesive for Fast, Low Temperature Cures

2014 ◽  
Vol 919-921 ◽  
pp. 2099-2104 ◽  
Author(s):  
Ben Wei Zhu ◽  
An Lin ◽  
Fu Xin Gan
Keyword(s):  
Low Temperature ◽  
Oxalic Acid ◽  
Heat Source ◽  
Vinyl Ester ◽  
High Performance ◽  
Vinyl Ester Resin ◽  
Chemical Heat ◽  
Two Component ◽  
Early Strength ◽  
The Stability

An high performance two-component structural anchor adhesive based on vinyl ester resin is synthesized by adding the toughener to improve the material brittleness and bringing in chemical heat source to reduce the affection of the environment on chemical reaction and it can be cured in the damp or in the environment with water by adding the water-absorbable filler.Compound stabilizer consisted of inhibitor and oxalic acid improve the stability of the pro-accelerated vinyl ester resin.The adhesive exhibites high-early-strength developing, excellent bong strength with “can’t dry”substrate and can cure rapid in lower temperature.it allows construction crews to install threaded rod or rebar in concrete that is too damp or soaked to bond with other adhesives.

The stability of the flow of an elastic-viscous liquid in a curves channel

1963 ◽  
Vol 274 (1358) ◽  
pp. 371-385 ◽  
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Viscous Liquid ◽  
Critical Reynolds Number ◽  
Curved Channel ◽  
Main Effect ◽  
The Stability

Consideration is given to the stability of the flow of an idealized elastico-viscous liquid in a narrow curved channel, the motion being due to a pressure gradient acting around the channel. It is shown that the main effect of the elasticity of the liquid is to lower the value of the critical Reynolds number at which instability occurs.

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