ZONA6 Versus the Doublet-Lattice Method for Unsteady Aerodynamics on Lifting Surfaces

T HE purpose of this Note is to clarify the frequency-dependence issue of ZONA6 and the doublet-lattice method (DLM) commented on by Rodden [1]. The DLM [2] is an unsteady flow extension of the vortex-lattice method (VLM) that was proposed by Hedman [3] and Belotserkovskii [4] during the mid-1960s to compute the steady aerodynamics on lifting surfaces. The VLM is a low-order steady aerodynamic panel method, because the vortex singularity is concentrated along the quarter-chord line on each aerodynamic box. By the mid-1970s, Woodward’s method [5] further advanced the steady panel methods with a distributed singularity over the complete aerodynamic box, and they are therefore higher-order methods than VLM. ZONA6 [6] is an unsteady flow extension of Woodward’s method and is therefore a higher-order method than the DLM. In this Note, we first clarify the meaning of low-order and highorder methods from the steady aerodynamic sense. Then the comparison between the ZONA6 and DLM solutions on the BAH wing [7] is presented to demonstrate that ZONA6 requires fewer aerodynamic boxes than the DLM for a converged unsteady aerodynamic solution.