Leading-edge tubercle modifications to the biomimetic wings

Abstract

An experimental investigation was conducted to better understand the effects of the humpback whale flipper's tubercles on biomimetic models. Different configurations of tubercles were investigated for five biomimetic flipper models by performing force measurement experiments at the Reynolds number of 5.0 × 104, 8.0 × 104, and 1.2 × 105 and surface oil flow visualization at Re = 1.2 × 105. The experiments were carried out with five different test models: two baseline models, one having a smooth and one having a tubercle leading-edge (LE); two simply designed tubercle models with uniform distribution; and a proposed tubercle model having a more realistic approach. It is proposed to create a tubercle pattern of a flipper model by summing two wave functions. The results indicated that the models with LE tubercles improved lift, delayed stall angle, and reduced drag compared to the baseline model. Irrespective of the Reynolds number, the model C3, which was created with a more realistic approach, performs better compared to baseline and other tubercle models. It has been seen that the maximum improvement in lift coefficient is achieved by approximately 18% with the C3 model at Re = 5.0 × 104. According to flow visualization results, the laminar separation bubble formed in the smooth baseline model was replaced by a counter-rotating vortex pairs (CRVPs) in the tubercle models. The improvement of the aerodynamic characteristics is due to the CRVPs formed by the interaction of the LE tubercles with each other and wavelike trailing-edge flow separation pattern. One of the significant findings to emerge from this study is that a more realistic approach has the potential to obtain better performance than a model with a uniform distribution of tubercles.