THE STUDY OF FLOW PAST MULTIPLE CYLINDERS AT HIGH REYNOLDS NUMBERS


Abstract
Flow past circular cylinders and square cylinders at high Reynolds numbers are simulated by improved delayed detachededdy simulation (IDDES), including a circular cylinder, a square cylinder, two tandem circular cylinders and two tandem square cylinders. The mean drag coefficient, the RMS values of lift coefficient and the Strouhal number are computed for various Reynolds numbers, which show a good agreement with previous experimental and numerical simulation data. It is found that the effect of Reynolds number on the global quantities for square cylinders is not much in this range of Reynolds numbers, which is different for circular cylinders. There is no drag crisis phenomenon for flow past a square cylinder at $2.0\times 1{0}^{3}<\mathit{Re}<1.0\times 1{0}^{7}$. The Strouhal number is Reynoldsindependent for $\mathit{Re}>2.0\times 1{0}^{3}$, and the Reynoldsindependent is also observed for the mean drag coefficient and the RMS lift coefficient. Simulation for two tandem circular cylinders is performed at Reynolds numbers of $2.2\times 1{0}^{4}$ and $3.0\times 1{0}^{6}$ for five different spacing $L$ to diameter $D$ ratios: $L/D=2.0$, 2.5, 3.0, 3.5 and 4.0. At the critical spacing (${L}_{c}/D)$ there is found a distinct steplike jump of mean drag coefficient and RMS lift coefficient of the subcritical Reynolds number of $2.2\times 1{0}^{4}$, and the mean drag coefficient of the downstream circular cylinder is negative for $L/D<{L}_{c}/D$. However, the mean drag coefficient and the RMS lift coefficient are seen to be slightly affected by spacing for $\mathit{Re}=3.0\times 1{0}^{6}$, and the mean drag coefficient of the downstream circular cylinder is always positive. Flow past two tandem square cylinders is considered at Reynolds numbers of $1.6\times 1{0}^{4}$ and $\mathit{Re}=1.0\times 1{0}^{6}$. The abrupt change in mean drag coefficient and RMS lift coefficient at the critical spacing is clearly seen on both upstream and downstream square cylinders for both Reynolds numbers. When $L/D<{L}_{c}/D$, the mean drag coefficient of the downstream cylinder is negative for both Reynolds numbers.

