Flow around six in-line square cylinders

2012 ◽  
Vol 710 ◽  
pp. 195-233 ◽  
Author(s):  
C. M. Sewatkar ◽  
Rahul Patel ◽  
Atul Sharma ◽  
Amit Agrawal
Keyword(s):  
Reynolds Number ◽  
Flow Regime ◽  
Lift Coefficient ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Square Cylinders ◽  
Chaotic Nature ◽  
Regime Map ◽  
Flow Regime Map

AbstractThe flow around six in-line square cylinders has been studied numerically and experimentally for $0. 5\leq s/ d\leq 10. 0$ and $80\leq \mathit{Re}\leq 320$, where $s$ is the surface-to-surface distance between two cylinders, $d$ is the size of the cylinder and $\mathit{Re}$ is the Reynolds number. The effect of spacing on the flow regimes is initially studied numerically at $\mathit{Re}= 100$ for which a synchronous flow regime is observed for $0. 5\leq s/ d\leq 1. 1$, while quasi-periodic-I, quasi-periodic-II and chaotic regimes occur between $1. 2\leq s/ d\leq 1. 3$, $1. 4\leq s/ d\leq 5. 0$ and $6. 0\leq s/ d\leq 10. 0$, respectively. These regimes have been confirmed via particle-image-velocimetry-based experiments. A flow regime map is proposed as a function of spacing and Reynolds number. The flow is predominantly quasi-periodic-II or chaotic at higher Reynolds numbers. The quasi-periodic and chaotic nature of the flow is due to the wake interference effect of the upstream cylinders which becomes more severe at higher Reynolds numbers. The appearance of flow regimes is opposite to that for a row of cylinders. The Strouhal number for vortex shedding is the same for all the cylinders, especially for synchronous and quasi-periodic-I flow regimes. The mean drag (${C}_{Dmean} $) experienced by the cylinders is less than that for an isolated cylinder, irrespective of the spacing. The first cylinder is relatively insensitive to the presence of downstream cylinders and the ${C}_{Dmean} $ is almost constant at 1.2. The ${C}_{Dmean} $ for the second and third cylinders may be negative, with the value of ${C}_{Dmean} $ increasing monotonically with spacing. The changes in root mean square lift coefficient are consistent with changes in ${C}_{Dmean} $. Interestingly, the instantaneous lift force can be larger than the instantaneous drag force on the cylinders. These results should help improve understanding of flow around multiple bluff bodies.

An Experimental Investigation of Flow Patterns During Condensation of HFC Refrigerants in Horizontal Micro-Fin Tubes

2019 ◽  
Vol 27 (01) ◽  
pp. 1950010
Author(s):  
Sanjeev Singh ◽  
Rajeev Kukreja
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Flow Regimes ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Regime Map ◽  
Fin Tubes ◽  
Flow Regime Map

Condensation heat transfer coefficients and flow regimes in two different horizontal micro-fin tubes are examined during the condensation of refrigerants R-134a and R-410A. The present investigation has focused on determination and prediction of condensation heat transfer coefficients and finding the interrelation between heat transfer coefficients and the prevailing flow regimes. During flow visualization, flow regimes have been captured using borosilicate glass tube at inlet and outlet of the test condenser using high speed digital camera. Stratified, stratified wavy, wavy annular, annular, slug and plug flows have been observed at different mass fluxes and vapor qualities of the refrigerants. The observed flow regimes are compared with the existing flow regime maps proposed by Breber et al. [Prediction of horizontal tube side condensation of pure components using flow regime criteria, J. Heat Transfer 102 (1980) 471–476], Tandon et al. [A new flow regime map for condensation inside horizontal tubes, J. Heat Transfer 104 (1982) 763–768.] and Thome et al. [Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, Int. J. Heat Mass Transfer 46 (2003) 3365–3387.] Thome et al. [Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, Int. J. Heat Mass Transfer 46 (2003) 3365–3387.] flow regime map shows good agreement with experimental data.

Simulation of flow across a row of transversely oscillating square cylinders

2011 ◽  
Vol 680 ◽  
pp. 361-397 ◽  
Author(s):  
C. M. SEWATKAR ◽  
ATUL SHARMA ◽  
AMIT AGRAWAL
Keyword(s):  
Reynolds Number ◽  
Oscillation Frequency ◽  
Amplitude Ratio ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Oscillation Amplitude ◽  
Flow Regimes ◽  
Flow Parameters ◽  
Square Cylinders ◽  
Wake Interaction

A numerical study of flow across a row of transversely oscillating square cylinders (of diameter d) has been undertaken using the lattice Boltzmann method, for a better understanding of fluid–structure interaction problems. The effects of cylinder oscillation frequency ratio (fe/fo, where fe is the cylinder oscillation frequency and fo is the corresponding vortex shedding frequency for stationary row of cylinders), amplitude ratio (A/d), non-dimensional spacing between the cylinders (s/d) and Reynolds number (Re) on ensuing flow regimes and flow parameters have been studied to understand the flow physics. Six different flow regimes observed in this study are the quasi-periodic non-lock-on-I, synchronous lock-on, quasi-periodic lock-on, quasi-periodic non-lock-on-II, synchronous non-lock-on and chaotic non-lock-on. It is observed that the range of the lock-on regime depends upon the relative dominance of incoming flow and cylinder motion. Although the lock-on regime in the case of Re = 80, s/d = 4 and A/d = 0.2 is substantially larger as compared to that for a single oscillating cylinder, the range of the lock-on regime shrinks with a reduction in the cylinder spacing, increase in the Reynolds number or decrease in the oscillation amplitude. It is also observed that the wake interaction behind the cylinders weakens with an increase in fe/fo, Re, A/d or s/d, leading to the formation of independent wakes and synchronous nature of the flow. For fe/fo ≥ 1.2, independent and intact oscillating wakes are noted and an additional frequency (wake oscillation frequency) is obtained in the time series of the lift coefficient. Although it was expected that the complexity in the wake interaction would increase with cylinder oscillation or amplitude ratio, an opposite effect (that is, formation of independent wakes) is noted from the results.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

Loss Characteristics of Orifices and Nozzles

1978 ◽  
Vol 100 (3) ◽  
pp. 299-307 ◽  
Author(s):  
S. H. Alvi ◽  
K. Sridharan ◽  
N. S. Lakshmana Rao
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Discharge Coefficient ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Center Line ◽  
Laminar Regime ◽  
Variation Of Parameters ◽  
Turbulent Flow Regime

Loss characteristics of sharp-edged orifices, quadrant-edged orifices for varying edge radii, and nozzles are studied for Reynolds numbers less than 10,000 for β ratios from 0.2 to 0.8. The results may be reliably extrapolated to higher Reynolds numbers. Presentation of losses as a percentage of meter pressure differential shows that the flow can be identified into fully laminar regime, critical Reynolds number regime, relaminarization regime, and turbulent flow regime. An integrated picture of variation of parameters such as discharge coefficient, loss coefficient, settling length, pressure recovery length, and center line velocity confirms this classification.

scholarly journals Effect of Cylinder Gap Ratio on The Wake of a Circular Cylinder Enclosed by Various Perforated Shrouds

CFD letters ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 51-68
Author(s):  
Nurul Azihan Ramli ◽  
Azlin Mohd Azmi ◽  
Ahmad Hussein Abdul Hamid ◽  
Zainal Abidin Kamarul Baharin ◽  
Tongming Zhou
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Control Method ◽  
Lift Coefficient ◽  
Base Case ◽  
Bluff Bodies ◽  
Ansys Fluent ◽  
Gap Ratio ◽  
Spacing Ratio

Flow over bluff bodies produces vortex shedding in their wake regions, leading to structural failure from the flow-induced forces. In this study, a passive flow control method was explored to suppress the vortex shedding from a circular cylinder that causes many problems in engineering applications. Perforated shrouds were used to control the vortex shedding of a circular cylinder at Reynolds number, Re = 200. The shrouds were of non-uniform and uniform holes with 67% porosity. The spacing gap ratio between the shroud and the cylinder was set at 1.2, 1.5, 2, and 2.2. The analysis was conducted using ANSYS Fluent using a viscous laminar model. The outcomes of the simulation of the base case were validated with existing studies. The drag coefficient, Cd, lift coefficient, Cl and the Strouhal number, St, as well as vorticity contours, velocity contours, and pressure contours were examined. Vortex shedding behind the shrouded cylinders was observed to be suppressed and delayed farther downstream with increasing gap ratio. The effect was significant for spacing ratio greater than 2.0. The effect of hole types: uniform and non-uniform holes, was also effective at these spacing ratios for the chosen Reynolds number of 200. Specifically, a spacing ratio of 1.2 enhanced further the vortex intensity and should be avoided.

scholarly journals Experimental Study of Rigid and Flexible Tandem Wing for Micro Aerial Vehicle

2021 ◽  
Vol 85 (2) ◽  
pp. 33-43
Author(s):  
Wan Mazlina Wan Mohamed ◽  
Mohd Azmi Ismail ◽  
Muhammad Ridzwan Ramli ◽  
Aliff Farhan Mohd Yamin ◽  
Koay Mei Hyie ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Unmanned Aerial Vehicle ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Micro Aerial Vehicle ◽  
Flexible Wing ◽  
Vehicle Structure ◽  
Aerial Vehicle ◽  
Wing Skin ◽  
Rigid Wing

Unmanned aerial vehicle is becoming increasingly popular each year. Now, aeronautical researchers are focusing on size minimization of unmanned aerial vehicle, especially drone and micro aerial vehicle. The lift coefficient of micro aerial vehicle has wing dimension of 12 cm and mass of less than 7 g. In the present study, with the aid of 3D printer, polylactic acid material was used to develop the micro aerial vehicle structure for tandem wing arrangement. The materials for rigid wing skin and flexible wing skin were laminating film and latex membrane, respectively. The present work elaborates the lift coefficient profiles on rigid wing skin and flexible wing skin at wing flapping frequency of 11 Hz, three different Reynolds numbers of 14000, 19000 and 24000, and five different angles of attacks between 0° and 50°. According to the results obtained, the lift coefficient decreased as the Reynolds number increased. The lift coefficient increased up to 9 as the angle of attack increased from 0° to 50° at the Reynolds number of 14000 for flexible wing skin. The results also showed that the lift coefficient of flexible wing skin was higher than that of rigid wing skin at the attack angle of10° and below, except for the Reynolds number of 14000.

scholarly journals Wake Modifications in Confined Flows Due to the Presence of a Downstream Cylinder in Staggered Arrangement

2018 ◽  
Vol 7 (4.27) ◽  
pp. 132
Author(s):  
Ahmad H. A Hamid ◽  
Mohd H. Jamaludin ◽  
Mohd H. M. Noh ◽  
Mohd A. M. Sapardi
Keyword(s):  
Strouhal Number ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Single Cylinder ◽  
Square Cylinders ◽  
Staggered Arrangement ◽  
Time Variations ◽  
Confined Flows

In the present study, confined flows around two square cylinders in staggered arrangement were numerically investigated. Cross-flow and streamwise center-to-center spacings of one- and three-cylinder diameters, respectively, were considered. Simulations were carried out at Reynolds numbers Re = 50,100,150 and 180, where the resulting wakes are laminar and periodic. Results indicate that the presence of the downstream cylinder tends to reduce the Strouhal number, amplitude and the time-averaged lift coefficient of the upstream cylinder relative to the single cylinder cases. Furthermore, the time variations of upstream cylinder’s lift coefficient behave similar to that of a single cylinder.  

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