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Stalnov O.,University of Southampton | Ben-Gida H.,Technion - Israel Institute of Technology | Kirchhefer A.J.,Boundary Layer Wind Tunnel Laboratory | Guglielmo C.G.,University of Western Ontario | And 3 more authors.
PLoS ONE | Year: 2015

We study the role of unsteady lift in the context of flapping wing bird flight. Both aerodynamicists and biologists have attempted to address this subject, yet it seems that the contribution of unsteady lift still holds many open questions. The current study deals with the estimation of unsteady aerodynamic forces on a freely flying bird through analysis of wingbeat kinematics and near wake flow measurements using time resolved particle image velocimetry. The aerodynamic forces are obtained through two approaches, the unsteady thin airfoil theory and using the momentum equation for viscous flows. The unsteady lift is comprised of circulatory and non-circulatory components. Both approaches are presented over the duration of wingbeat cycles. Using long-time sampling data, several wingbeat cycles have been analyzed in order to cover both the downstroke and upstroke phases. It appears that the unsteady lift varies over the wingbeat cycle emphasizing its contribution to the total lift and its role in power estimations. It is suggested that the circulatory lift component cannot assumed to be negligible and should be considered when estimating lift or power of birds in flapping motion. © 2015 Stalnov et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

El-Gammal M.,University of Western Ontario | El-Gammal M.,Boundary Layer Wind Tunnel Laboratory | El-Gammal M.,McMaster University | Naughton J.W.,University of Wyoming | And 2 more authors.
Journal of Aircraft | Year: 2010

A study was conducted to employ direct measurements of surface pressure and skin friction to characterize the physics of the surface flow around a divergent trailing-edge (DTE) airfoil. The study also focused on estimating the profile drag from direct measurements accurately and compare it with that estimated from a survey in the airfoil far wake. The airfoil surface coordinates were selected to match the distribution of surface pressure, momentum thickness, and shape factor over the aft 20% of the chord to those on the DTE Douglas Long Beach Airfoil DLBA 243 in transonic flight. The model was constructed from a conventional glass-fiber reinforced composite sandwich. The two airfoil surfaces were tripped at 5%downstream of the leading edge by installing surface protrusions of 2 mm in diameter, 1 mm in height, and spaced 5 mm apart in the cross-stream direction. Velocity measurements upstream and in the far wake of the airfoil were obtained with pitot tubes.

Doddipatla L.S.,University of Western Ontario | Doddipatla L.S.,Boundary Layer Wind Tunnel Laboratory | Naghib-Lahouti A.,University of Western Ontario | Naghib-Lahouti A.,Boundary Layer Wind Tunnel Laboratory | And 3 more authors.
40th AIAA Fluid Dynamics Conference | Year: 2010

Wake flows behind two dimensional bodies are mainly dominated by two coherent structures, namely the Karman-Benard vortices and the streamwise vortices, also referred to as rolls and ribs respectively. The three dimensional wake instabilities lead to distinct instability modes (mode-A, mode-B and mode-C or mode S) depending on the flow Reynolds number and geometric shape. The present investigation explores the mechanism in which the flow transitions to three dimensionality in the near wake of a profiled leading edge and blunt trailing edge body. A combination of Planar Laser Induced Fluorescence visualizations and Particle Image Velcoimetry measurements are conducted for Reynolds numbers ranging from 250 to 2300. The results indicate that three instability modes (mode-A, mode-B and mode-C) appear in the wake transition to three dimensionality, and their order of appearance does not occur through the traditional route as observed in circular cylinder flows. It is found that mode-C instability with a spanwise spacing of 2.4D (D being the trailing edge thickness) dominates the near wake development. © 2010 by hangan. Published by the American Institute of Aeronautics and Astronautics, Inc.

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