The force generation mechanism of lifting surfaces with flow separation

• Published in: Ocean engineering 2021-11, Vol.239, p.109749, Article 109749
• Main Authors: Viola, Ignazio Maria, Arredondo-Galeana, Abel, Pisetta, Gabriele
• Format: Article
• Language: English
• Subjects: Hydrofoil/blade hydrodynamics; Impulse theory; Leading-edge separation; Lifting surface; Lifting-line theory; Wing/sail aerodynamics
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2021.109749

Fins, wings, blades and sails can generate lift and drag in both attached and separated flow conditions. However, the common understanding of the lift generation mechanism holds only for attached flow conditions. In fact, when massive flow separation occurs, the underlying assumptions of thin airfoil theory and lifting line theory are violated and the concept of bound circulation cannot be applied. Therefore, there is a need to develop an intuitive understanding of the force generation mechanism that does not rely on these assumptions. This paper aims to address this issue by proposing a paradigm based on established concepts in theoretical fluid mechanics, and impulse theory in particular. The force generation can be intuitively associated with the vorticity field, which can be gathered with computational fluid dynamics or particle image velocimetry. This paradigm reconciles key known results about wing aerodynamics, and provides designers of lifting surfaces a measurable objective to optimise the shape in separated flow conditions. It will hopefully underpin both a deeper understanding of how lift and drag are generated, and the development of low order models in different fields of application. [Display omitted] •The force generation of lifting surfaces explained with impulse theory.•A paradigm for the lift generation mechanism of stalled wings.•Explanation of the force contribution associated with free vorticity in the fluid.