Cylinder wake flow in confined channel and its active control by sweeping jets

The wake dynamics of the flow past a confined circular cylinder and its active control by sweeping jets (SWJs) and steady jets (SJs) positioned at the front stagnation points were experimentally investigated using particle image velocimetry and pressure measurements. Experiments were conducted across a range of Reynolds numbers (Re, based on the incoming flow velocity and the cylinder diameter) from 10,000 to 45,000 and blockage ratios ( \(\beta\) $\beta$ ) of \(1/2\) $1/2$ , \(1/3\) $1/3$ , \(1/4\) $1/4$ , and \(1/5\) $1/5$ . A comprehensive comparison between the current results and existing literature on natural flow dynamics fills the knowledge gap and reveals that confinement gradually reduces the time-average pressure coefficient ( \(C_{{\text{p}}}\) $C_{\text{p}}$ ) and increases the drag coefficient ( \(C_{{\text{D}}}\) $C_{\text{D}}$ ) and Strouhal number (St). The interaction between the wake and lateral wall shear layer gradually increased as \(\beta\) $\beta$ increased. Both SWJs and SJs effectively suppressed wake fluctuations, and the statistical characteristics of the flow field and proper orthogonal decomposition analysis indicated a consistent flow control mechanism between the two methods. However, the SJs introduced external fluctuations and unbalanced forces in the forward flow field, resulting in a wake flow asymmetry. By contrast, SWJs provide more uniform control and superior flow control effectiveness and efficiency.