Effect of sail fullness on the aerodynamic performance of ringsail parachutes
GAO Chang, LI Yanjun, YU Li, NIE Shunchen
Key Laboratory of Aircraft Environment Control and Life Support, Ministry of Industry and Information Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Abstract：[Objective] Previous studies on ringsail parachutes based on computational fluid dynamics (CFD) mainly focused on the slotted structures of the canopy or the overall fabric permeability of ringsail parachutes. Ringsail parachutes with different sail structures, including the upward-exhaust ringsail (UER) and downward-exhaust ringsail (DER), are proposed to allow for different exhaust directions. Sail structures usually account for larger areas and are more complex; therefore, they have a more significant influence on the aerodynamics of parachutes. However, systematic research on the sail structures of ringsail parachutes is lacking. Therefore, the effect of sail structural designs on the deceleration performance of ringsail parachutes is unclear.[Method] In this study, the numerical models of the flow field around a parachute with different exhaust sail directions are established according to the aerodynamic shape of a ringsail parachute under steady descent. The influences of the sail exhaust direction and sail structure fullness on aerodynamic performance are explored via CFD. Wake, jet flow, and canopy surface pressure are explored, the deceleration and stability performances of parachutes with different sail exhaust directions are compared, and the action mechanism is analyzed. Sail fullness is varied as the main parameter, and the relationship between sail configurations and ringsail aerodynamics is analyzed.[Results] The results reveal the following:(1) Jet flow existed at crescent slots. In a UER parachute, jet flow converged in the downstream air column, which reduced the drag and generates an additional restoration moment on the parachute. Therefore, the UER featured smaller drag coefficients but better stabilities than the DER. (2) The UER was significantly affected by geometric permeability; therefore, with increasing sail fullness, the drag coefficient of the UER increased. The jet flow direction was determined by sail fullness. Therefore, under the effect of the reverse thrust of the jet flow, the drag coefficient of the DER decreased with increasing sail fullness. (3) Owing to the effect of the main tail vortex downstream of the canopy and the jet flow at the crescent slots of the sail, the UER and DER featured optimal fullness values for stability. (4) Considering the deceleration and stability performances of ringsail parachutes with different sail fullness values, the aerodynamic performance of ringsail parachutes was optimal at a sail fullness value of K=1.10.[Conclusions] Through the CFD-based numerical calculations of the steady descent states of ringsail parachutes, this study explores the effects of different exhaust directions and sail fullness on the aerodynamic performance of ringsail parachutes. Our research can provide a certain reference for the structural designs and performance analyses of ringsail parachutes.
高畅, 李岩军, 余莉, 聂舜臣. 帆片结构张满度变化对环帆伞气动性能的影响[J]. 清华大学学报（自然科学版）, 2023, 63(3): 322-329.
GAO Chang, LI Yanjun, YU Li, NIE Shunchen. Effect of sail fullness on the aerodynamic performance of ringsail parachutes. Journal of Tsinghua University(Science and Technology), 2023, 63(3): 322-329.
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2023, Vol. 63 
