Browsing by Author "Şahin, Mehmet"

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Citation - WoS: 6
Citation - Scopus: 6
Propulsive Performance of Plunging Airfoils in Biplane Configuration
(American Institute of Physics Inc., 2022) Yücel, S. Banu; Şahin, Mehmet; Ünal, Mehmet Fevzi
Biplane configuration of pure plunging airfoils is investigated in terms of vortex dynamics both experimentally and numerically by utilizing particle image velocimetry and unstructured finite volume solver of incompressible unsteady Navier-Stokes equations. Experiments are carried out to disclose the vortex shedding and interaction mechanisms for various values of frequency and amplitude of the plunging motion. For the non-dimensional plunge amplitude with respect to the chord of airfoil h = 0.2, the effect of the reduced circular frequency based on chord length and the free stream velocity k = 1 and 10 are considered, whereas for h = 0.3, k = 2, 4, 8, and 10 cases are examined. Influence of the plunge amplitude is studied for h = 0.25 at k = 2.5 and for h = 0.0875, 0.15, and 0.3 at k = 4. Numerical simulations are performed to investigate the effect of phase difference on vortex structures and propulsive characteristics, such as thrust and Froude efficiency. Two cases having the highest thrust and efficiency values k = 2.5, h = 0.25, and k = 4, h = 0.15 value couples are selected for the phase angle of φ = 0 °, φ = 90 °, φ = 180 °, and φ = 270 °. Opposed plunge, φ = 180 °, was found as the most efficient amongst all phase angles that were investigated, where φ = 90 ° is beneficial in lift production. Additionally, three-dimensional simulations indicate no significant three dimensionalities for the parameters used herein.
Citation - Scopus: 2
Strong Transient Effects of the Flow Around a Harmonically Plunging Naca0012 Airfoil at Low Reynolds Numbers
(Springer, 2015) Yücel, S. Banu; Şahin, Mehmet; Ünal, M. Fevzi
Abstract The flow pattern around a NACA0012 airfoil undergoing harmonic plunging motion corresponding to the deflected wake phenomenon reported by Jones and Platzer (Exp Fluids 46:799–810, 2009) is investigated in detail using direct numerical simulations. An arbitrary Lagrangian–Eulerian formulation based on an unstructured side-centered finite volume method is utilized in order to solve the incompressible unsteady Navier–Stokes equations. The Reynolds number is chosen to be 252, and the reduced frequency of plunging motion (k = 2?fc/U?) and the plunge amplitude non-dimensionalized with respect to chord are set to be 12.3 and 0.12, respectively, as in the experimental study of Jones and Platzer (2009). The present numerical simulations reveal a highly persistent transient effect, and it takes two orders of magnitude larger duration than the heave period to reach the time-periodic state. In addition, the three-dimensional simulation reveals that the flow field is three-dimensional for the parameters used herein. The calculation reproduces the deflected wake and shows a good agreement with the experimental wake pattern. The instantaneous vorticity contours, finite-time Lyapunov exponent fields and particle traces are presented along with the aerodynamic parameters including the lift and thrust coefficients.