On the Interfoil Spacing and Phase Lag of Tandem Flapping Foil Propulsors

• DOI: 10.5957/jspd.150027
• Publication Date: 2017-10-18T03:17:40Z
• Authors: Brenden P. Epps; Luke E. Muscutt; Bernard T. Roesler; Gabriel D. Weymouth; Bharathram Ganapa...
• Keywords: Propulsor; Flapping; Propulsive efficiency; Freestream; Lift (data mining)

The aim of this article is to provide a theoretical basis upon which advance and deploy novel tandem flapping foil systems for efficient marine propulsion. We put forth three key insights into hydrodynamics related their choreography, propulsive efficiency, unsteady loading. In particular, we propose that the performance aft depends on new nondimensional number, s/Uτ, interfoil separation s normalized by distance freestream U advects in one period, τ. Additionally, show how loading can be mitigated through choice phase lag. 1. Introduction Marine propulsion has been an important engineering problem since time Archimedes (287–212 BC) (Carlton 1994). evolution propulsor design from classic screw modern propeller primarily driven considerations efficiency. A hydrodynamically low friction losses, turbulent ability manipulate incident vorticity, stable persistent jet-type wake. it composed lifting surfaces with high aspect ratio large lift-to-drag ratio. Although propellers offer advantages regard mechanical simplicity (just need turn shaft!), they have practical limitations place upper bounds overall hydrodynamic such as due cavitation at tip speeds. Research isolated foils demonstrated up 87% efficiency (Anderson et al. 1998), nearly achieving ideal actuator disk. However, single-foil not shortcomings, oscillations thrust, side forces, no redundancy. Many other nontraditional propulsors also suffer these flaws or are simply inefficient. Biomimetic concept designs trade-offs recently reviewed Fish (2013). One promising involves in-line (two hydrofoils, other). Recent research indicates single may possible arrangement (Akhtar 2007; Boschitsch 2014). Tandem solve operational problems associated foil, inconsistent thrust force.