scholarly journals Properties of the flow around two rotating circular cylinders in side-by-side arrangement with different rotation types

2014 ◽  
Vol 18 (5) ◽  
pp. 1487-1492 ◽  
Author(s):  
Cheng-Xu Tu ◽  
Fu-Bin Bao ◽  
Long Huang
Keyword(s):  
Flow Pattern ◽  
Turbulence Intensity ◽  
Rotational Speed ◽  
Cross Flow ◽  
Type A ◽  
Shear Layers ◽  
Circular Cylinders ◽  
Flow Modification ◽  
Gap Flow ◽  
Optimal Value

The field characteristics of two side-by-side rotating circular cylinders in a cross-flow is investigated under different rotation types, at T/D = 1.11,1.6, and 3, respectively (T is the center spacing between the cylinders, and D is the cylinder diameter). A similar flow pattern which is the most efficient to narrow the lowpressure area is identified for rotation type A, independent of T/D ratio, and two typical flow patterns are found under different spacings for rotation type B and type C, respectively. It is confirmed that there is an optimal rotational speed of 1.7-2, under rotation type A to attenuate the vortices, velocity drop, and turbulence intensity tremendously. As rotational speed increases to the optimal value, both the velocity drop and turbulence intensity decrease and their distributions are smooth. The results indicate that the shear layers which are accelerated following the free-stream direction would have significant influence on the flow modification, and different rotation types actually arrange these shear layers in diverse ways to change the flow pattern. Pitch ratio is capable to transform the gap flow, which is usually including the shear layers referred, thus this parameter can modify the wake of the two cylinders at different rotation types.

Flow-pattern identification for two staggered circular cylinders in cross-flow

2000 ◽  
Vol 411 ◽  
pp. 263-303 ◽  
Author(s):  
D. SUMNER ◽  
S. J. PRICE ◽  
M. P. PAÏDOUSSIS
Keyword(s):  
Particle Image ◽  
Cross Flow ◽  
Flow Patterns ◽  
Shear Layers ◽  
Circular Cylinders ◽  
Angle Of Incidence ◽  
Vortex Pairing ◽  
Image Velocimetry ◽  
Pitch Ratio ◽  
Flow Pattern Identification

The flow around two circular cylinders of equal diameter, arranged in a staggered configuration, was investigated using flow visualization and particle image velocimetry for centre-to-centre pitch ratio P/D = 1[ratio ]0 to 5.0 and angle of incidence. α = 0° to 90°. Experiments were conducted within the low subcritical Reynolds number regime, from Re = 850 to 1900. Nine flow patterns were identified, and processes of shear layer reattachment, induced separation, vortex pairing and synchronization, and vortex impingement, were observed. New insight was gained into previously published Strouhal number data, by considering the flow patterns involved. The study revealed that vortex shedding frequencies are more properly associated with individual shear layers than with individual cylinders; more specifically, the two shear layers from the downstream cylinder often shed vortices at different frequencies.

Flow-Induced Forces on a Cylinder for Different Wall Confinements at High Reynolds Numbers (3.5×105)

1975 ◽  
Vol 97 (2) ◽  
pp. 110-117
Author(s):  
P. Y. Chen ◽  
P. E. Doepker
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Interference Effects ◽  
High Reynolds Numbers ◽  
Gap Flow ◽  
High Reynolds ◽  
Flow Medium ◽  
Available Information

The nearness of a cylinder to a wall has an important effect on the flow-induced forces exerted on that cylinder, particularly when the cylinder is relatively large compared to the cross section of the flow channel. This paper describes an investigation of wall interference effects that occur when crossflow-induced forces are exerted on circular cylinders with moderately large blockages (d/h = 0.2 to 0.33) at high Reynolds numbers (3.5 × 105 – 1.2 × 106). The results show that, within the range studied, the gap flow velocity is the correct flow velocity to compensate for wall interference effects. The data reported here represent the first available information on experimental cross-flow-induced forces at such high Reynolds numbers using water as a flow medium.

A Closer Investigation of the Mean Aerodynamic Forces for Two Staggered Circular Cylinders in Cross-Flow

2002 ◽  
Author(s):  
D. Sumner ◽  
M. D. Richards
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Incidence Angle ◽  
Cross Flow ◽  
Local Maximum ◽  
Circular Cylinders ◽  
Aerodynamic Forces ◽  
Gap Flow ◽  
The Mean ◽  
Small Increments

Two circular cylinders of equal diameter in a staggered configuration, with centre-to-centre pitch ratios of P/D = 1.125 – 4.0, were tested in the subcritical Reynolds number regime, at Re = 3.0×104 – 8.0×104. The incidence angle of the cylinder configuration was varied in small increments from α = 0° – 90° and the mean aerodynamic forces were measured on both the upstream and downstream cylinders. Based on the force measurements, the behaviour of the cylinders was broadly grouped into three categories, depending on P/D. For closely spaced staggered configurations, P/D = 1.125 – 1.25, the aerodynamic forces on both the upstream and downstream cylinders varied significantly with α. Several critical incidence angles were identified for each cylinder that corresponded to local maximum, minimum, or discontinuous behaviour in the forces, which were related to shear layer reattachment and the influence of the gap flow. For moderately spaced staggered configurations, P/D = 1.5 – 2.5, shear layer reattachment and the subsequent transition to gap flow at small α were responsible for the inner lift peak, a corresponding minimum drag, and a loss of lift with increasing α, which becomes more abrupt as P/D is increased. For widely spaced staggered configurations, P/D = 3.0 – 4.0, the two cylinders undergo Ka´rma´n vortex shedding for the entire range of α. At small α, the forces on the downstream cylinder are affected by vortex impingement, and the outer lift peak replaces the inner lift peak. This outer lift peak exhibits some sensitivity to the Reynolds number.

scholarly journals Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Francesco Fornarelli ◽  
Antonio Lippolis ◽  
Paolo Oresta
Keyword(s):  
Nusselt Number ◽  
Flow Pattern ◽  
Richardson Number ◽  
Near Field ◽  
Circular Cylinders ◽  
Momentum Exchange ◽  
Force Coefficients ◽  
The Earth ◽  
Spacing Ratio ◽  
Oscillatory Character

In this paper, we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are isothermal and they are aligned with the earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center-to-center spacing (s = 3.6d–4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found, and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=−1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact, the transition occurs due to rearrangement of the near-field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.

Experimental study on filtering papermaking black liquor by dynamic blade crossflow membrane

2020 ◽  
Vol 35 (3) ◽  
pp. 464-470 ◽  
Author(s):  
Wenjie Zhao ◽  
Junfei Wu ◽  
Fushan Chen
Keyword(s):  
Molecular Weight ◽  
Experimental Study ◽  
Environmental Pollution ◽  
Rotational Speed ◽  
Membrane Filtration ◽  
Black Liquor ◽  
Cross Flow ◽  
Transmembrane Pressure ◽  
Filtration Equipment ◽  
Fundamental Reason

AbstractThe fundamental reason for the environmental pollution caused by the papermaking industry is the inadequate treatment of the black liquor. How to dispose of the lignin macromolecules, which is the main pollutants in the black liquor, is the key to addressing the environmental pollution. At present, cross-flow membrane filtration is one of the effective ways to retain and recycle lignin macromolecules in black liquor. The paper proposes the adoption of a dynamic blade cross-flow membrane filtration equipment provided by German BOKELA company to treat papermaking black liquor. The experiment shows that when the black liquor is treated with dynamic blade rotation cross-flow, the membrane with a molecular weight cut-off of nanofiltration (NP010) delivers the best retaining effect, with 28 % more lignin in black liquor than that in untreated black liquor. Meanwhile, when the blade rotational speed reaches 300 rpm and the transmembrane pressure is 0.5 or 2 bar, the flux of black liquor through nanofiltration NP010 is relatively desirable.

scholarly journals Energy and Exergy Analyses of Tube Banks in Waste Heat Recovery Applications

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2094 ◽  
Author(s):  
Mustafa Erguvan ◽  
David MacPhee
Keyword(s):  
Energy Efficiency ◽  
Reynolds Number ◽  
Heat Recovery ◽  
Waste Heat ◽  
Cross Flow ◽  
Exergy Efficiency ◽  
Circular Cylinders ◽  
Published Data ◽  
Energy And Exergy ◽  
Exergy Analyses

In this study, energy and exergy analyses have been investigated numerically for unsteady cross-flow over heated circular cylinders. Numerous simulations were conducted varying the number of inline tubes, inlet velocity, dimensionless pitch ratios and Reynolds number. Heat leakage into the domain is modeled as a source term. Numerical results compare favorably to published data in terms of Nusselt number and pressure drop. It was found that the energy efficiency varies between 72% and 98% for all cases, and viscous dissipation has a very low effect on the energy efficiency for low Reynolds number cases. The exergy efficiency ranges from 40–64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers. The results could be useful in designing more efficient heat recovery systems, especially for low temperature applications.

Strouhal Number for VIV Excitation of Long Slender Structures

2018 ◽  
Author(s):  
Andrew E. Potts ◽  
Douglas A. Potts ◽  
Hayden Marcollo ◽  
Kanishka Jayasinghe
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Degrees Of Freedom ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Shedding Frequency ◽  
Eddy Shedding

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder. A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15. Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.

scholarly journals Effect of Rotational Speed on the Stability of Two Rotating Side-by-side Circular Cylinders at Low Reynolds Number

2018 ◽  
Vol 27 (2) ◽  
pp. 125-134
Author(s):  
Huashu Dou ◽  
Shuo Zhang ◽  
Hui Yang ◽  
Toshiaki Setoguchi ◽  
Yoichi Kinoue
Keyword(s):  
Reynolds Number ◽  
Rotational Speed ◽  
Low Reynolds Number ◽  
Circular Cylinders ◽  
Low Reynolds ◽  
The Stability
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