Control of flow and heat transfer over two inline square cylinders

Laminar flow around and heat transfer from two inline square cylinders under an active flow control (uniform blowing and suction) are numerically investigated at Reynolds numbers of 70-150, a Prandtl number of 0.71, and a cylinder-gap spacing (G) ratio of G/d = 1-5, where d is the cylinder side. A finite-volume code based on a collocated grid arrangement is employed in the two-dimensional numerical simulations. Uniform blowing and suction are applied to the upstream cylinder only (referred to as UFC) or applied to both cylinders (referred to as OFC). The purpose of using these two flow controls is to reduce time-mean and fluctuating forces and to suppress vortex shedding. The noncontrol case is referred to as the reference case where vortex shedding occurs from both cylinders for G/d >= 3 and from the downstream cylinder only for G/d < 3. For UFC, vortex shedding from the upstream cylinder is suppressed for G/d = 1-5 examined. A drag reduction of more than 50% occurs for the upstream cylinder with G/d = 1-5, while the downstream cylinder has such a high drag reduction for G/d >= 3 only. In the case of OFC, vortex shedding from either cylinder is suppressed while the time-mean and fluctuating forces reduce for the entire G/d range. The maximum reduction in the total drag force (sum of both cylinders) is about 70%. The blowing hinders heat transfer from the cylinders while the suction enhances it.