Influence of Dimple Orientation on Drag Characteristics of Circular Cylinder at Subsonic Flow

Abstract

This study investigates the drag reduction potential of a cylinder with combinations of dimpled and smooth surfaces, examining the effects of various dimple placements on drag coefficient (C_D) across a range of Reynolds Numbers (Re). Experimental results reveal that strategic dimple placements on the cylinder’s windward side effectively reduce drag by influencing boundary layer behavior. Specifically, the configurations with 60^o dimpled and 150^o smooth and 120^o dimpled and 60^o smooth surfaces consistently demonstrated the lowest drag coefficients, especially at higher Reynolds Numbers, where delayed flow separation was achieved. Conversely, configurations with limited dimple coverage, such as 30^o dimpled and 150^o smooth, produced higher drag coefficients, indicating less effective boundary layer control. Full dimple coverage (180^o dimpled) showed significant drag reduction only at higher Reynolds Numbers, while higher drag persisted at lower speeds. These findings suggest that partial dimple coverage on the windward side can optimize drag reduction by promoting early boundary layer transition, making such configurations advantageous for applications requiring efficient aerodynamic and hydrodynamic performance. The overall results indicate that dimple placement is crucial in influencing drag, providing insights for optimizing surface modifications for improved aerodynamic efficiency.