Fluid dynamic effects between adjacent streamline bodies have a conspicuous role in drag reduction. One typical example is a dolphin drafting. When two dolphins such as a mother and a calf swim side by side, the calf seldom flaps its tail fin, indicating the calf utilizes the fluid dynamic force between the two bodies as a thrust. This force is generated by the Venturi effect. In this study, wind tunnel tests were conducted with two streamline bodies of different sizes that mimicked the mother and the calf dolphins to clarify the fluid dynamic effects between two bodies at various relative positions. In consequence, the increase of friction drag by the acceleration of flow between two bodies and the thrust generation by the Venturi effect were confirmed as well as the optimum position to maximize the thrust, indicating the possibility of effective design of airplanes with external appendages.
