Model for sectional leading-edge vortex lift for the prediction of rotating samara seeds performance

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>This article presents a development of a simple analytical aerodynamic model capable of describing the effect of leading-edge vortices (LEVs) on the lift of rotating samara wings. This analytical model is based on the adaptation of Polhamus’ method to develop a sectional two-dimensional lift function, which was implemented in a numerical blade element model (BEM) of a rotating samara blade. Furthermore, wind tunnel experiments were conducted to validate the numerical BEM and to assess the validity of the newly developed analytical lift function. The results showed good agreement between the numerical model and the experimental measurements of rotational speed and rate of descent of the samara wing. The results were also compared with numerical predictions using BEM but adopting different lift coefficient expressions available in literature. This research contributed towards efficient aerodynamic modelling of the lift generated by LEVs on rotating samara wings for performance prediction, which could potentially be used in the design of bio-inspired rotary micro-air vehicles.</jats:p>

Sectional Leading Edge Vortex Lift and Drag Coefficients of Autorotating Samaras

“…There are uncertainties concerning whether the Polhamus model can be fully applicable to the conditions of insect and samara flights, where the maximum operating α are much higher (α ≈ 45°, 80°, respectively). Nonetheless, a few researchers [23,27,63] have applied the Polhamus model to describe the lift and drag of low aspect ratio flapping/revolving wings.…”

“…A simple yet insightful numerical modelling technique is the use of Blade Element Momentum Theory (BEM), which has been adopted extensively to describe the flight and the forces produced by the samara [1,19,26,27,[48][49][50]. The low-order BEM models were shown to be effective and efficient in assessing the critical aerodynamic parameters affecting the flight of samaras.…”

“…However, some researchers argued that the BEM might be inappropriate for samara studies, being unable to capture the fully localised unsteady effects and the influence of wake on the total forces [51,52]. Furthermore, one of the main shortfall of BEM models is that the calculated aerodynamic forces are dependent on the sectional lift (C l ) and sectional drag coefficients (C d ) and unfortunately, there is still ambiguity on what is the most appropriate C l and C d expression to describe the samara LEV [26,27].…”

“…Hence, there is no guarantee that these C L functions will equally suit the samara. For samaras specifically, Rezgui et al [27] (2020) tried to assess the validity of the Polhamus-based model in describing the 2D sectional lift of a samara with a LEV. The authors introduced an adapted 2D Polhamus function as well as different C l and C d models within a BEM model, developed to predict the performance of samaras in autorotational flight.…”

Preview of the 75thAnniversary of aerospace engineering at the University of Bristol online collection

“…Other papers focussed upon aerodynamics include studies on a 2D space time method for unsteady flows including geometric and topological changes [4], compressible laminar boundary layers [5], the development of a cell-vertex upwind scheme for two-dimensional supersonic Euler flows [6], the modelling of the vortex lift of rotating samara seeds [7], and the use of pulse responses for the system reduction of 2D unsteady flows generated using CFD [8].…”