Settling characteristics of bidisperse dilute suspension in the vortex shedding regime

2020 ◽  
Vol 32 (9) ◽  
pp. 093310 ◽  
Author(s):  
Ali Abbas Zaidi
Keyword(s):  
Vortex Shedding ◽  
Dilute Suspension ◽  
Settling Characteristics

Evolution of unstable system.

2015 ◽  
Vol 9 (3) ◽  
pp. 2487-2502 ◽  
Author(s):  
Igor V. Lebed
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Stokes Flow ◽  
Stable Solution ◽  
The State ◽  
Unstable System ◽  
Unstable Flow ◽  
Unstable Solutions ◽  
Vortex Shedding Modes ◽  
Hydrodynamics Equations

Scenario of appearance and development of instability in problem of a flow around a solid sphere at rest is discussed. The scenario was created by solutions to the multimoment hydrodynamics equations, which were applied to investigate the unstable phenomena. These solutions allow interpreting Stokes flow, periodic pulsations of the recirculating zone in the wake behind the sphere, the phenomenon of vortex shedding observed experimentally. In accordance with the scenario, system loses its stability when entropy outflow through surface confining the system cannot be compensated by entropy produced within the system. The system does not find a new stable position after losing its stability, that is, the system remains further unstable. As Reynolds number grows, one unstable flow regime is replaced by another. The replacement is governed tendency of the system to discover fastest path to depart from the state of statistical equilibrium. This striving, however, does not lead the system to disintegration. Periodically, reverse solutions to the multimoment hydrodynamics equations change the nature of evolution and guide the unstable system in a highly unlikely direction. In case of unstable system, unlikely path meets the direction of approaching the state of statistical equilibrium. Such behavior of the system contradicts the scenario created by solutions to the classic hydrodynamics equations. Unstable solutions to the classic hydrodynamics equations are not fairly prolonged along time to interpret experiment. Stable solutions satisfactorily reproduce all observed stable medium states. As Reynolds number grows one stable solution is replaced by another. They are, however, incapable of reproducing any of unstable regimes recorded experimentally. In particular, stable solutions to the classic hydrodynamics equations cannot put anything in correspondence to any of observed vortex shedding modes. In accordance with our interpretation, the reason for this isthe classic hydrodynamics equations themselves.

Some modeling issues on trailing-edge vortex shedding

AIAA Journal ◽  
2001 ◽  
Vol 39 ◽  
pp. 787-793
Author(s):  
Wei Ning ◽  
Li He
Keyword(s):  
Vortex Shedding ◽  
Trailing Edge ◽  
Edge Vortex

COMPARISON OF LES WITH DSM, k-ε AND EXPERIMENTS FORTURBULENT VORTEX SHEDDING FLOW PAST 2D SQUARE CYLINDER

1994 ◽  
Vol 59 (459) ◽  
pp. 49-56 ◽  
Author(s):  
Shigehiro SAKAMOTO ◽  
Akashi MOCHIDA ◽  
Shuzo MURAKAMI ◽  
Wolfgang RODI
Keyword(s):  
Vortex Shedding ◽  
Square Cylinder ◽  
Flow Past

Behaviour of Mechanically Blended Return-Sludge in Absence of Substrate

1970 ◽  
Vol 5 (1) ◽  
pp. 34-54
Author(s):  
Shyam D. Bokil ◽  
Jatinder K. Bewtra
Keyword(s):  
Activated Sludge ◽  
Suspended Solids ◽  
Treatment Plant ◽  
Aeration Rate ◽  
Batch Experiments ◽  
Sludge Treatment ◽  
Waring Blender ◽  
Settling Characteristics

Abstract Nine sets of batch experiments, each of ten to twelve days duration, were conducted in the laboratory on return-sludge samples collected from activated sludge treatment plant at Windsor. The thickened sludge samples were blended daily in a waring blender and were continuously aerated in twelve-litres capacity jars. Parallel runs were made on control sludge samples which were not blended. Amongst the parameters varied were the speed and frequency of blending and the aeration rate. The effects of these variables on progressive bio-degradation of volatile suspended solids and the settling characteristics of the sludge were determined. Blended sludge showed significant improvement in the rate of bio-degradation and its settling characteristics as compared to the control unblended sludge

Methods for determining the settling velocity profiles of solids in storm sewage

1996 ◽  
Vol 33 (9) ◽  
pp. 117-125 ◽  
Author(s):  
Emmanuelle Aiguier ◽  
Ghassan Chebbo ◽  
Jean-Luc Bertrand-Krajewski ◽  
Peter Hedges ◽  
Naomi Tyack
Keyword(s):  
Suspended Solids ◽  
Settling Velocity ◽  
Test Procedure ◽  
Velocity Profiles ◽  
Test Methods ◽  
Efficient Treatment ◽  
Experimental Procedure ◽  
Comparative Tests ◽  
Settling Process ◽  
Settling Characteristics

Recently, research has shown that a settling process is an efficient treatment for the removal of suspended solids from storm sewage. In order to design settling tanks, there is a need to determine the settling velocity characteristics of these solids. Devices and test methods for measuring settling velocities of solids in storm sewage have been developed by researchers. A literature review has revealed that the settling velocity profiles obtained with some methods (Chebbo, 1992), (Michelbach and Wohrle, 1993) and (Tyack et al., 1993) are very different. In order to explain why the results are different and to quantify the influence of the experimental procedure on the settling velocity grading curves, we have compared the selected methods when tested with the same sample and we have studied the effects of the conservation of the sample before the test, of the concentration of solids in the device and of the nature of the water on the settling velocity profiles. The results of the comparative tests indicate that the settling velocities are significantly lower with both the Cergrene and Aston methods than with the UFT test procedure. Moreover, the study has shown that the settling characteristics of solids change with time, that the use of sewage liquor rather than demineralised water or drinking water can change the results of the measurement and that the higher the concentration of solids, the greater the velocity of settled particles.

Experiences with sludge settleability in different process alternatives for nutrient removal

1996 ◽  
Vol 33 (12) ◽  
pp. 137-146 ◽  
Author(s):  
Kjær Andreasen ◽  
Lars Sigvardsen
Keyword(s):  
Nutrient Removal ◽  
Plant Layout ◽  
Filamentous Microorganisms ◽  
Positive Effect ◽  
Sludge Settleability ◽  
Settling Characteristics ◽  
P Removal

SVI and DSVI were measured three times at almost 100 Danish nutrient removal plants and the filamentous microorganisms were subsequently characterized in the laboratory. Information about the plant layout and the operation was collected by means of a questionnaire. In general, the sludge settleability index becomes worse by the introduction of nutrient removal. Among nutrient removal plants the best settling characteristics are found among plants with biological P removal and the poorest among the plants that perform simultaneous denitrification. When compared to iron products, aluminium products in some cases seem to reduce the filament number and improve the settling characteristics in plants that apply simultaneous precipitation for P removal. Selectors may have a positive effect on the filament number but the effect may not be enough to prevent bulking.

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