Seongyun Hwang’s research while affiliated with Ulsan National Institute of Science and Technology and other places

This study investigates the effects of rotor–rotor interaction on the wake and thrust characteristics of a small tandem rotor operating in a crosswind. Flow velocity and force measurements were conducted in a wind tunnel with two rotors arranged parallel to a crosswind. The results show that the rotor–rotor interaction significantly influences the wake characteristics and thrust generations of the tandem rotor and its effects vary depending on the crosswind speed and distance between rotor tips. In the tandem rotor configuration, the front rotor wake prevents the crosswind flow from reaching the rear rotor wake, thereby reducing the crosswind influence on it. However, under the strong rotor–rotor interaction, such as that caused by high crosswind speeds and short distances between rotor tips, the wakes of both rotors collide with each other and rapidly break down as they proceed downward. Tip-vortex characteristics are also affected by rotor–rotor interaction, which is investigated in terms of variations in the time-averaged tip-vortex trajectory and dissipation ratio with the strength of rotor–rotor interaction. These wake variations by rotor–rotor interaction lead to a decrease in thrust coefficients of the front and rear rotors, with a more significant reduction observed for the rear rotor. The thrust of the rear rotor is more significantly reduced as the crosswind speed increases and the distance between rotor tips narrows. This is mainly attributed to the increased axially induced velocity near the leading tips on the advancing side, retreating side, and centerline.

In this study, the aerodynamic effects of the inflation of a paraglider wing (canopy) are investigated at the maximum chord Reynolds number of 330000. The aerodynamic forces and surface flow patterns were compared between the inflated and uninflated canopy models in a wide range of angles of attack. The stall angle and maximum lift coefficient of the inflated model are approximately 80 % and 38 % greater than those of the uninflated model. Before stall, dot- and line-shaped separation bubbles are formed on the inflated and uninflated models, respectively. The dot-shaped separation bubbles remain to a much higher angle of attack than the line-shaped one, with little change in the size and location. For the inflated model near stall, the flow is partially separated in the spanwise center, and the separation bubbles remaining are distorted. After stall, the canopy inflation has little effect on aerodynamic performance as the flow is fully separated.