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Frequency domain Unsteady Lifting-Line Theory (ULLT) provides a means bywhich the aerodynamics of oscillating wings may be studied at low computationalcost without neglecting the interacting effects of aspect ratio and oscillationfrequency. Renewed interest in the method has drawn attention to severaluncertainties however. Firstly, to what extent is ULLT practically useful forrectangular wings, despite theoretical limitations? And secondly, to whatextent is a complicated wake model needed in the outer solution for goodaccuracy? This paper aims to answer these questions by presenting a completeULLT based on the work of Sclavounos, along with a novel ULLT that considersonly the streamwise vorticity and a Prandtl-like pseudosteady ULLT. These arecompared to high fidelity Euler CFD for cases of rectangular wings at multipleaspect ratios and oscillation frequencies. The results of this work establishULLT as a low computational cost model capable of accounting for interactingfinite-wing and oscillation frequency effects, and identify the aspect ratioand frequency regimes where the three ULLTs are most accurate. This researchpaves the way towards the construction of time-domain or numerical ULLTs whichmay be augmented to account for non-linearities such as flow separation.

Unsteady lifting-line theory and the influence of wake vorticity on aerodynamic loads