An experimental investigation of reducing the wake length at a low speed by passive flow control and biomimetic application

This study explores the use of biomimetic designs in passive flow control to reduce wake length at low speed, aiming to enhance aerodynamic efficiency. Inspired by nature's optimization of fluid dynamics in birds and marine life, this research investigates the applicability of these biological principles to improve aerospace engineering designs, particularly for low Reynolds number flows relevant to Unmanned Aerial Vehicles (UAVs). The experimental setup involved a smoke visualization wind tunnel to examine flow patterns around several wing models. These models incorporated bio-inspired elements, mimicking shark skin riblets and humpback whale tubercles, strategically positioned to delay flow separation and minimize wake length. The wing models, designed using 3D modeling software and printed via a 3D printer, were tested at various angles of attack in a smoke visualization wind tunnel by measuring their wake length via image processing. Experiments were carried out in two stages; types of protrusion were investigated on the first stage and the position of a selected protrusions examined in the second stage. The findings indicate significant differences in wake length reduction across the models, with certain biomimetic adaptations, especially optimized triangular protrusions inspired by shark skin, showing notable improvements in aerodynamic performance at higher angles of attack. Among different models in the first stage, Model B was the most effective model in aerodynamic performance with a drag reduction effect of 18% compared to the reference model NACA 0018. In the second stage experiments, Model B-15 showed the most effective aerodynamic result by reducing the wake length by 30% in the range of α=0˚-20˚, while the reduction for Model B-20 was 26%. The results offer valuable insights into the design of efficient, low-speed flight vehicles, suggesting that biomimetics could lead to innovative designs with higher performance and energy efficiency. This research emphasizes the potential of integrating biomimetic principles into passive flow control strategies.