Some Characteristics of High Waves in Closed Channels Approaching Kelvin-Helmholtz Instability

1977 ◽  
Vol 99 (2) ◽  
pp. 339-346 ◽  
Author(s):  
E. Kordyban
Keyword(s):  
Surface Pressure ◽  
Water Waves ◽  
Internal Flow ◽  
Flow Patterns ◽  
Pressure Variation ◽  
Helmholtz Instability ◽  
Wave Celerity ◽  
Theoretical Considerations ◽  
Wave Shapes

The characteristics of water waves produced by flowing air in closed channels were studied to uncover the effects of surface pressure variation. From theoretical considerations, it is proposed that the point of onset of the Kelvin-Helmholtz instability for such waves may be found from 1.35ρaρwVc2ghc=1 Photographs of internal flow patterns and wave shapes confirm the occurrence of this instability, but the theoretically predicted reduction in wave celerity does not occur. The wave celerity for high waves was found to be predictable by the formula C=0.191gLtanh2πhwL1/2 The measured height to length ratios for the highest observed waves are of the order of 0.1.

scholarly journals Computational assessment of wind flow field on and around atypical buildings

2020 ◽  
Author(s):  
Rajasekarababu KB
Keyword(s):  
Surface Pressure ◽  
Pressure Coefficient ◽  
Tall Buildings ◽  
Ground Level ◽  
Pressure Variation ◽  
Middle Level ◽  
Computational Results ◽  
Pressure Coefficients ◽  
Building Surfaces ◽  
Side Face

Abstract This article provides an overview of pressure coefficients ( Cp ) on atypical tall buildings with the application of CFD. Various modifications in architectural shapes on tall buildings eventually lead to a reduction in the wind load on building surfaces. The surface pressure on conventional (Square and rectangular) buildings is relatively different in comparison to other tall buildings. This study is to evaluate the surface pressure coefficient over rectangular, taper and setback buildings. The computational results show that the taper building has 7% Cp rise at ground level ( y/H= 0.225) in the windward face, and 34% Cp fall at the middle level ( y/H= 0.475) in the side face when compared with the rectangular building. Whereas for the setback building, Cp at ground level near setback ( y/H= 0.225) has reduced to about 25% and about 6% at the middle level ( y/H= 0.475) in windward than that in the rectangle building. Also, the side faces of the setback showed a 15% drop in Cp than other buildings. In leeward face, Cp is reduced to 56% near setback at the top of the building ( y/H= 0.725). This valuation of the Cp on these buildings shows that the effect of setbacks on building reduces the pressure variation on all faces and the downstream wake vortices.

scholarly journals Internal flow patterns of a droplet pinned to the hydrophobic surfaces of a confined microchannel using micro-PIV and VOF simulations

2019 ◽  
Vol 370 ◽  
pp. 444-454 ◽  
Author(s):  
Guang Yang ◽  
Alexandros Terzis ◽  
Ioannis Zarikos ◽  
S. Majid Hassanizadeh ◽  
Bernhard Weigand ◽  
...  
Keyword(s):  
Internal Flow ◽  
Flow Patterns ◽  
Hydrophobic Surfaces ◽  
Micro Piv

scholarly journals A case study on internal flow patterns of the two-phase closed thermosyphon (TPCT)

2020 ◽  
Vol 18 ◽  
pp. 100586
Author(s):  
S. Sichamnan ◽  
T. Chompookham ◽  
T. Parametthanuwat
Keyword(s):  
Internal Flow ◽  
Flow Patterns ◽  
Two Phase

Internal Flow and Noise Investigations About the Cross-Flow Fan With Different Blade Angles

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Hua Ouyang ◽  
Jie Tian ◽  
You Li ◽  
Zhiming Zheng ◽  
Zhaohui Du
Keyword(s):  
Relative Velocity ◽  
Numerical Solutions ◽  
Cross Flow ◽  
Internal Flow ◽  
Flow Patterns ◽  
Far Field ◽  
Noise Characteristics ◽  
Aerodynamic Performances ◽  
Field Noise ◽  
Cross Flow Fan

The experimental and numerical studies have been carried out to investigate the flow and the noise characteristics of the three impellers with different blade angles in a cross-flow fan (CFF). First, the aerodynamic performances of the fan with these impellers are obtained experimentally, and the averaged flow patterns inside the impellers are measured by the three-hole probe. Second, the far-field noise generated by CFF with different impellers has been measured in a semianechoic chamber under different throttling conditions. Third, the two-dimensional unsteady CFD simulations have been performed by commercial software. The internal flow patterns influenced by the different blade angles have been summarized through the computational results. The accuracy of the calculations is validated by the corresponding experimental ones. The detail analysis has been carried out on the unsteady vortex flow properties of the three impellers, which is considered to be the main factor that influences the aerodynamic and aeroacoustic performance of the CFF. Finally, the relative far field noise generated by different impellers are evaluated by an empirical formula based on the assumption that the total sound pressure levels are proportional to the sixth power law of the relative velocity on the outer and inner circumferences of the impeller. The circumferential distributions of relative velocity are provided from the numerical solutions. The varying trends of predicted results agree well with the actual relative noise of the CFF with three different impellers.

Analysis of Power Plant Deaerator Storage Tank Instabilities

1981 ◽  
Vol 195 (1) ◽  
pp. 251-259 ◽  
Author(s):  
R R Cranfield ◽  
D H Wilkinson
Keyword(s):  
Power Plant ◽  
Water Waves ◽  
Storage Tank ◽  
Water Surface ◽  
Analytical Approach ◽  
Helmholtz Instability ◽  
Transient Load ◽  
Sequence Of Events ◽  
Scale Models ◽  
Late Generation

In some power plant deaerators storage tank steam is caused to flow over the surface of the water on its way to the condensing head. This steam flow, which may become very large under transient load operation, low pressure feed heater bypassing or isolation, may create water waves, a hydraulic gradient and possibly spray which carries over into the deaerator head via the steam transfer pipe to result in high differential pressure. This may lead to head flooding, surging discharge, tray stack damage, and also give rise to problems with associated components; for example vent condenser flooding. Steam transfer pipes may constitute a forcing system resulting in tank contents sloshing and severe vibration. These events in turn may precipitate an instability (the Kelvin-Helmholtz instability) whereby waves may grow to bridge the gap between water surface and tank crown to form a water-piston. A piston so formed is rapidly propelled along the tank to impact with a hammer-like blow causing serious internal and external damage and jeopardizing safety. The sequence of events finally precipitating the onset of the water piston is complex and renders an analytical approach which might establish design criteria difficult, for this reason simple modelling is suggested. This paper describes such studies using one-twelfth scale models of late generation 500-660 MW units, from which the parameters governing instability are evaluated.

Square-Cylinder Flow Characteristics Modulated Using Upstream Control Rod

2012 ◽  
Vol 28 (2) ◽  
pp. 279-289 ◽  
Author(s):  
S. C. Yen ◽  
S. F. Wu
Keyword(s):  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Square Cylinder ◽  
Control Rod ◽  
Pressure Profiles ◽  
Spacing Ratio ◽  
Cylinder Flow ◽  
Upstream Control

AbstractThe flow patterns, vortex-shedding frequency and aerodynamic performance of the square-cylinder flow were modulated using an upstream control rod. Additionally, the flow behaviors were examined using various Reynolds numbers, rotation angles, and spacing ratios. The flow patterns were visualized using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow modes were characterized based on the kinematics theory. Moreover, the vortex-shedding frequencies behind upstream control rod and the square cylinder were detected using two hot-wire anemometers. The surface pressure on square cylinder was determined using a linear pressure scanner. Then, the aerodynamic parameters were calculated using the surface-pressure profiles. Three characteristic flow modes — single, attached, and bi-vortex-street — were categorized by varying the Reynolds number and spacing ratio. In the attached mode, the position of upstream control rod determined the flow characteristics. Furthermore, in the attached mode, the mean drag force of the square cylinder is about 57% lower than of single-square cylinder.

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