Drag reduction on a circular cylinder through the use of architectured woven coatings

Abstract

The relative motion between fluids and structures generates aerodynamic drag which leads to energy consumption. This increases when functional constraints limit the geometry to bluff body shapes. Although there exist solutions for reducing the drag of such bodies, nowadays devices must satisfy multiple functionalities. The 3D Woven, 3DW, material adheres to this necessity through a periodic, porous architecture, manufactured via 3D weaving techniques. Initially, 3DW was developed to perform heat transfer tasks whilst maintaining the required structural properties. The present work, investigated 3DW material to reduce the aerodynamic drag of circular cylinders. The customization of 3DW structural properties supports the replacement of a solid portion of the cylinder with a porous insert, providing an additional saving in power consumption through weight reduction, provided that the stiffness and strength are maintained. Three configurations with the 3DW placed at the Stagnation, the Separation, and at the Leeward regions were assessed. The direct drag measurements and the static pressure readings at the inner and at the outer surfaces of 3DW material suggested suitable mechanisms for the drag reduction. When placed at the Leeward region, the mean streamlines were deflected within the medium, delaying the separation and increasing the base pressure recovery. Despite the flow similarities flow, the Separation configuration generated detrimental results suggesting the importance of the configuration geometry on the performance. Alternatively, when the coating was placed at the Stagnation region, the incoming flow penetrated the substrate, outflowing near the coating boundaries. Here, it promoted turbulence within the boundary layer and delayed the flow separation. Subsequent modifications of the material topology confirmed the insights on the physics and highlighted the relevance of the internal flows for drag reduction. Besides, the near-wake analysis suggested the impact of the boundary layer velocity profile on the Strouhal number value, additionally to the base pressure coefficient.