caa a22 4500 606198334 CHVBK 20210128100933.0 cr unu---uuuuu 210128e20150401xx s 000 0 eng 10.1007/s00348-015-1946-2 doi (NATIONALLICENCE)springer-10.1007/s00348-015-1946-2 Influence of structural flexibility on the wake vortex pattern of airfoils undergoing harmonic pitch oscillation [Elektronische Daten] [B. Monnier, A. Naguib, M. Koochesfahani] Reported herein is an investigation of the influence of the structural flexibility of sinusoidally pitching airfoils on the pattern of vorticity shed into the wake. For rigid airfoils, it is well known that, depending on the oscillation frequency and amplitude, this pattern takes the form of the classical or reverse von Kármán vortex street. The pattern may be characterized by the vortex circulation (Γ o ), vortex-to-vortex streamwise and cross-stream spacing (a and b, respectively), and vortex core radius (R). In the present work, these four parameters are obtained from particle image velocimetry measurements in the wake of airfoils consisting of a rigid "head” and flexible "tail” at chord Reynolds number of 2010 for different tail flexibilities. The results show that flexible airfoils exhibit the switch from classical to reverse von Kármán vortex street (i.e., change in the sign of b) at a reduced frequency of oscillation lower than their rigid counterpart. At a given oscillation frequency, the Strouhal number at which this switch occurs is smallest for a given airfoil structural flexibility; which becomes stiffer with increasing frequency. Using Strouhal number based on the actual trailing edge oscillation amplitude, reasonable scaling is found of the dependence of not only b but also Γ o , a and R on the motion and structure parameters for all airfoils investigated. These results are complemented with analyses using a vortex array model, which together with the identified scaling of the wake vortex parameters, provide basis for the computation of the net thrust acting on the airfoil. Springer-Verlag Berlin Heidelberg, 2015 Monnier B. Michigan State University, 48104, East Lansing, MI, USA aut Naguib A. Michigan State University, 48104, East Lansing, MI, USA aut Koochesfahani M. Michigan State University, 48104, East Lansing, MI, USA aut Experiments in Fluids Springer Berlin Heidelberg 56/4(2015-04-01), 1-17 0723-4864 56:4<1 2015 56 348 https://doi.org/10.1007/s00348-015-1946-2 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-1946-2 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Monnier B. Michigan State University, 48104, East Lansing, MI, USA aut NATIONALLICENCE 700 1- Naguib A. Michigan State University, 48104, East Lansing, MI, USA aut NATIONALLICENCE 700 1- Koochesfahani M. Michigan State University, 48104, East Lansing, MI, USA aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/4(2015-04-01), 1-17 0723-4864 56:4<1 2015 56 348