2 results
Flow around six in-line square cylinders
- C. M. Sewatkar, Rahul Patel, Atul Sharma, Amit Agrawal
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- Journal:
- Journal of Fluid Mechanics / Volume 710 / 10 November 2012
- Published online by Cambridge University Press:
- 03 September 2012, pp. 195-233
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The flow around six in-line square cylinders has been studied numerically and experimentally for and , where is the surface-to-surface distance between two cylinders, is the size of the cylinder and is the Reynolds number. The effect of spacing on the flow regimes is initially studied numerically at for which a synchronous flow regime is observed for , while quasi-periodic-I, quasi-periodic-II and chaotic regimes occur between , and , 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 () 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 is almost constant at 1.2. The for the second and third cylinders may be negative, with the value of increasing monotonically with spacing. The changes in root mean square lift coefficient are consistent with changes in . 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.
Simulation of flow across a row of transversely oscillating square cylinders
- C. M. SEWATKAR, ATUL SHARMA, AMIT AGRAWAL
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- Journal:
- Journal of Fluid Mechanics / Volume 680 / 10 August 2011
- Published online by Cambridge University Press:
- 31 May 2011, pp. 361-397
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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.