Recirculating flow behind and unsteady forces on finite-span circular cylinders in a cross-flow

1991 ◽  
Vol 5 (2) ◽  
pp. 185-206 ◽  
Author(s):  
F. Baban ◽  
R.M.C. So
Keyword(s):  
Cross Flow ◽  
Circular Cylinders ◽  
Unsteady Forces ◽  
Finite Span ◽  
Recirculating Flow

Local Force Measurements on Finite-Span Cylinders in a Cross-Flow

1987 ◽  
Vol 109 (2) ◽  
pp. 136-143 ◽  
Author(s):  
V. K. Sin ◽  
Ronald M. C. So
Keyword(s):  
Free Stream ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Free Stream Turbulence ◽  
Finite Span ◽  
Present Technique ◽  
Unsteady Force

A technique employing a three-axis piezoelectric load cell is developed to measure local unsteady forces induced on cylinders placed in a cross flow. Verification of the technique is carried out with a two-dimensional circular cylinder. All measurements are made at a Reynolds number of ∼4.8 × 104 and a free-stream turbulence of ∼1.5 percent. The local two-dimensional unsteady lift measurement is found to be in excellent agreement with spanwise-averaged data reported in the literature, thereby validating the feasibility of the present technique. Steady and unsteady force measurements on finite-span circular cylinders are reported and compared with available data in the literature.

Unsteady forces on circular cylinders in a cross-flow

1989 ◽  
Vol 7 (5) ◽  
pp. 293-302 ◽  
Author(s):  
F. Baban ◽  
R. M. C. So ◽  
M. V. Ötügen
Keyword(s):  
Cross Flow ◽  
Circular Cylinders ◽  
Unsteady Forces

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.

Flow Dynamics Over Two Cylinders in Tandem Subjected to Different Heating Cases

2021 ◽  
Author(s):  
Rami Homsi ◽  
MD Islam ◽  
Yap Yit Fatt ◽  
Isam Janajreh
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Temperature Fields ◽  
Circular Cylinders ◽  
Transfer Coefficients ◽  
Extended Body ◽  
Heat Transfer Coefficients ◽  
Velocity Magnitude ◽  
Fluid Properties ◽  
Limiting Case

Abstract Heated and unheated flows with forced convection over two fixed circular cylinders in tandem are studied numerically for 80 ≤ Re ≤ 250 and 1 ≤ T* ≤ 2.3. Three different spacing ratios (L/D) = [2, 4, 8] are considered under three heating conditions. The scenarios considered are (1) heated upstream and unheated downstream cylinders, (2) unheated upstream and heated downstream cylinders and (3) heated upstream and downstream cylinders. These scenarios represent the limiting case for a cross-flow heat exchanger, where the downstream tubes are at increasingly lower or higher temperature for cooling or heating, respectively. The global aerodynamic forces on the cylinder as vortices shed was investigated. The flow is visualized by plotting the streamlines, temperature fields, and velocity magnitude contours for the different spacing ratios and compared to the flow regimes in literature namely, Extended-body, Reattachment, and Co-shedding regimes. The drag and surface heat transfer coefficients are analyzed for different scenarios. The effect of heating on the fluid properties and the resulted wakes in the flow are found to be strongly influenced by Re and L/D. The scenario of heated upstream and unheated downstream cylinders was found to increase the mean drag coefficient Cd on the upstream cylinder for L/D = 2 & 4 but is not as evident for the downstream cylinder. The heat transfer coefficient h on the upstream cylinder remained approximately the same regardless of a heated or unheated downstream cylinder. In contrast, h of the downstream cylinder decreases for the scenario of heated upstream and downstream cylinder.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

Two staggered circular cylinders of equal diameter in cross-flow

2005 ◽  
Vol 20 (2) ◽  
pp. 255-276 ◽  
Author(s):  
D. Sumner ◽  
M.D. Richards ◽  
O.O. Akosile
Keyword(s):  
Cross Flow ◽  
Circular Cylinders

Fluidelastic Instability of an Infinite Double Row of Circular Cylinders Subject to a Uniform Cross-Flow

1983 ◽  
Vol 105 (1) ◽  
pp. 59-66 ◽  
Author(s):  
S. J. Price ◽  
M. P. Paidoussis
Keyword(s):  
Aerodynamic Force ◽  
Mass Parameter ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Frequency Detuning ◽  
Complex Flow ◽  
Force Coefficient ◽  
Double Row ◽  
Mechanical Coupling ◽  
Fluid Damping

This paper represents the first stage of a fundamental investigation of the vibration phenomena induced in heat exchanger bundles subject to a cross-flow. Using aerodynamic force coefficient data, obtained experimentally from a static wind tunnel model, a linearized quasi-static analysis is employed to analyze the stability of an infinite double row of circular cylinders in uniform cross-flow. From the analysis it is shown that the instability is a result of the negative fluid damping forces, resulting from the complex flow pattern in the row. A new expression is obtained relating the critical velocity for the onset of instability to the damping parameter, the mass parameter and the pitch ratio of the cylinders. The expression is compared with experimental data available in the literature, from dynamic laboratory results, and a good correlation is obtained. Using this stability analysis the effect of mechanical coupling and frequency detuning, both between modes in one cylinder and modes in adjacent cylinders, is examined. In general it is shown that mechanical coupling is destabilizing and frequency detuning stabilizing.

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