Drag Mitigation of Trilobed Airship Hull through Aerodynamic Comparison with Conventional Single-Lobed Hull

Multilobed hybrid airships are being considered the next paradigm for reinvigorated utilization of lighter-than-air systems toward the realization of a green aviation future. However, increased epistemic understanding pertaining to their underlying complex aerodynamics in comparison to their conventional single-lobed counterparts is essential to augment the global implementation of these airships. This paper presents a comprehensive numerical investigation carried out at low subsonic speeds and a Reynolds number ($Re$) of $3.9\times {10}^5$ to capture the aerodynamics related to a trilobed airship hull in comparison to a single-lobed (conventional) airship hull based on the LOTTE profile. Postsolver validation, the study deliberates key aerodynamic aspects that need consideration while replacing a single-lobed airship with a trilobed airship. It is established that a trilobed hull with the same hull volume leads to significantly higher aerodynamic efficiency (109%) due to the increased lift coefficient in comparison to the conventional hull. However, reduced longitudinal stability and increased drag coefficient values (83.9%) with the difference being higher at higher angles are its biggest shortcomings. The paper makes use of the pressure coefficient as well as the flow-field description plots to decipher the alleviation of three-dimensional relieving, and the flow intermixing effects at the nose and stern portions, respectively in the case of trilobed hull leading to these aerodynamic deviations. Furthermore, the paper makes use of a webbed trilobed variant, to alleviate the aforementioned drag penalties by virtue of reduced flow separation in the stern portion. Notwithstanding, this benefit, a webbed trilobed variant leads to reduced lift coefficient values compared to the baseline trilobed hull variant. Hence, this paper underscores key aerodynamic differences between the conventional and trilobed hull variants and makes use of this understanding to mitigate drag penalty related to the latter by closing the gap between its three lobes.

This paper explores the aerodynamic aspects that need to be considered while making use of multilobed hybrid airships in place of conventional single-lobed hulls. Understanding these results can be helpful for modifying the preexisting multilobed hull models so that their utility can be enhanced within the air mobility sector leading to the realization of a sustainable aviation future. This aerodynamic comparison has been accomplished through a sequence of computational simulations carried out in low subsonic and highly turbulent flow conditions. The results show that the trilobed hull with the same volume as the conventional hull achieves a significantly higher lift-to-drag ratio (109%) due to its increased lift coefficient. However, the trilobed hull also exhibits reduced longitudinal stability and increased drag coefficient values (83.9%), particularly at higher angles. Various post-processing tools like pressure coefficient and flow-field description plots were used to underscore the flow physics related to these aerodynamic variations. Following this comprehensive comparison, the paper further presents a new trilobed hull variant called the webbed trilobed hull. Due to the inherent structure, flow associated with these modified hulls was modified leading to drag mitigation at the expense of reduced lift coefficient. Overall, this research sheds light on some key aerodynamic differences between the conventional and trilobed hull variants paving the way for design modification for improved efficiency and performance of the multilobed hulls.