Prediction of Vortex Initiation using an Unsteady Panel Method with an Integral-Boundary-Layer Calculation

Abstract

In our current work, we implement and evaluate the efficacy of a boundary layer parameter (𝐻 32 ) based low-order model to signal the onset of leading-edge vortex (LEV) initiation for low Re flows (O (10 4 )) . In an earlier work(AIAA Aviation Forum 2019, p.3590) using numerical simulations, it was proven that the shape factor parameter (𝐻 32 ) attains a critical value of ∼ 1.52 prior to the formation of dynamic stall vortex (DSV) irrespective of airfoil, motion kinematics. Numerical simulations spanned high pitch rate motions (𝐾 ≥ 0.1) and three leading edge radii (0.5 ≤ 𝑟 𝐿𝐸 ≤ 2.0) for three different pivot locations : leading-edge (LE), quarter-chord (QC) and half-chord (HC). This finding concurred with the 𝐻 32 value reported in literature for laminar separation (𝐻 32 = 1.515) in steady incompressible flows. In the second part of the effort, we focus on low-order prediction of LEV initiation using this criticality. This was achieved using an inviscid calculation of unsteady-airfoil velocity and pressure distributions, which serve as an input to a quasi-steady integral boundary layer (IBL) method. The results provided here demonstrate the effectiveness of 𝐻 32 in predicting leading-edge flow reversal. We show, by analysing different cases, that this inexpensive method has crucial ramifications in picking the appropriate 𝐿𝐸 𝑆𝑃 𝑐𝑟𝑖𝑡 for any given airfoil and motion combination. Hence, we eliminate the need for CFD, Experiments to obtain 𝐿𝐸 𝑆𝑃 𝑐𝑟𝑖𝑡 for a new parameter set.

Prediction of leading-edge-vortex initiation using criticality of the boundary layer

“…Preliminary results from authors' efforts were presented in Refs. [55] and [56], which addressed the first and second goals, respectively. In the current article, following the presentation of some essential background material on LESP and LEV initiation in Sect.…”