Analysis of Aerodynamic Interference Between Cylindrical-Float and Ellipsoidal-Float on Helicopter

At present, helicopter rescue has garnered increasing attention. However, existing research predominantly focuses on water impact and flotation stability, with limited attention given to the influence of emergency floats on helicopter aerodynamic characteristics. To address this gap, this study investigates the aerodynamic interference resulting from different configurations of emergency floats on the helicopter using numerical simulations via the RANS method. The flow field around the emergency float, helicopter fuselage, and helicopter-float combination are individually calculated through numerical simulations. Subsequently, the aerodynamic interference effects of initial (cylindrical-float) and modified (ellipsoidal-float) configurations of emergency floats on the helicopter are analyzed. It is found that emergency floats significantly impact the aerodynamic characteristics of the helicopter during forward flight. The cylindrical-float-helicopter combination exhibits a drag coefficient of approximately 0.059, representing a 48% increase compared to the helicopter without floats. Meanwhile, the ellipsoidal-float-helicopter combination demonstrates a drag coefficient of about 0.046, marking a 15% increase relative to the helicopter without floats. The aerodynamic interference also effects the emergency floats themself, with variations in pressure coefficients observed among different floats in the front and tail positions, while similarities are noted in the middle part. The differential pressure coefficients between the interior and exterior of the floats surpasses that between the upper and lower sections, primarily due to increased flow velocity between the float and fuselage. Through comparison, it is indicated that the ellipsoidal-floats reduce the aerodynamic impact on the helicopter compared to the cylindrical-floats, resulting in a smaller drag coefficient for the helicopter-float combination. This reduction is attributed to the smaller negative pressure area around the front and tail of the ellipsoidal float. Additionally, the weakening separation vortices when air flows through the ellipsoidal-float further mitigate the additional aerodynamic drag caused by the emergency float.