Pitch/Plunge Equivalence for Dynamic Stall of Swept Finite Wings

A high-fidelity numerical study is undertaken to expand the notion of pitch/plunge equivalence to finite, swept wings undergoing deep-dynamic stall and builds upon the analysis of straight wings in another paper by the authors [Pitch/Plunge Equivalence for Dynamic Stall of Unswept Finite Wings, AIAA Journal (submitted for publication)]. The wing has an aspect ratio of AR = 4 with a NACA 0012 section, a rounded tip, and a sweep angle of Lambda = 30 deg; it operates at a Reynolds number of Re-c = 2 x 10(5) and a Mach number of M-infinity = 0.1. Equivalent pure-pitch and pure-plungemotions at two different reduced frequencies are considered to assess pitch-induced apparent camber on the wing and its effects on the three-dimensional flow structure, surface topology, and aerodynamic loading. Regardless of the motion type or rate, the wing undergoes dynamic tip stall that is initiated through the outboard separation of a dynamic stall vortex as it lifts off the surface and forms into an arch vortex before ejecting into the wake. The pitching cases exhibit an advanced development and evolution in time of these features that are observed as variable amplifications of the aerodynamic loading, which is due predominantly to an apparent camber effect. Corrections to the total and sectional lift and moment coefficients are explored by extending steady thin-airfoil theory to pitching swept wings. Remarkably, the corrected plunge-equivalent histories provide a full collapse of the force and moment responses between the pitching and plunging cases, despite the delayed behavior of the flow structure. This equivalence and the similar process of dynamic stall should facilitate the comparison of experiments and/or simulations employing different motion types, even for finite-aspect-ratio and swept wings.

Automated summary

This high-fidelity numerical study aims to expand the concept of pitch/plunge equivalence to finite, swept wings undergoing deep-dynamic stall. The study evaluates the effects of pitch-induced apparent camber on the wing and its impact on flow structure, surface topology, and aerodynamic loading. The research finds that regardless of the motion type or rate, the wing experiences dynamic tip stall, with a faster development and evolution in the case of pitch motion. The study also explores the corrections to lift and moment coefficients and discovers that the corrected plunge-equivalent histories collapse the force and moment responses between pitch and plunge cases, despite the delayed behavior of the flow structure.