Manipulation of bumpy surface cylinders for flow control and heat transfer improvement

The present work aims at investigating laminar flow effects over bumped-surface circular cylinders at Reynolds number ≤ 200. Three bumpy cylinder surfaces are considered and studied, comprising square, triangular, and dimple surface shapes. The bumpy surfaces are placed on the upper surface of the cylinder and arranged between 0° and 90° from the front stagnation point of the cylinder. These angles include θ = 0○, 45○, and 90○. The flow characteristics, such as the lift and drag coefficients, as well as the Strouhal and Nusselt numbers, are evaluated. For all three examined bump shapes, it is demonstrated that when θ ≤ 45°, the amplitude of the drag coefficient is smaller than larger angles. It is also found that at θ = 90°, the magnitude of the drag coefficient is about 40% larger than test cases with θ ≤ 45°. It is found that the Nusselt number is dependent on the location of the bump on the leading surface of the cylinder. The critical angle of the bump's location is identified and introduced, which is θcm = 45°. While the minimum Nusselt number is obtained once the bump is located at θcm = 45°, the maximum Nusselt number is assessed at θ = 90° with approximately a 12% increment.