Investigation of Oscillating-Foil Power Generation in Constrained Flow

Hoke C. M., Young J., Lai J. C. S., Karakaş F., Zaloglu B., Fenercioglu I.

10th International Conference on Structural Dynamics (EURODYN), Rome, Italy, 10 - 13 September 2017, vol.199, pp.3450-3455 identifier identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 199
  • Doi Number: 10.1016/j.proeng.2017.09.450
  • City: Rome
  • Country: Italy
  • Page Numbers: pp.3450-3455
  • Istanbul Technical University Affiliated: Yes


This paper presents a numerical study of a 2D pitching and plunging flat plate foil operating in the vicinity of near side walls. The effects of the side wall proximity and the stroke reversal fraction are compared to previously published water tunnel experimental results and the resulting vortex structures are used to comment on the effect of the constrained flow on overall power generation. Three side wall distances are defined by the closest approach of the trailing edge of the foil during the flapping cycle, including d(w) = 0.1c, d(w) = 0.5c, and d(w) = 1.0c as well as 'Free Flow' case done with tunnel walls at a distance of 10.0c. The stroke reversal fraction determines how quickly the foil pitches at the top and bottom of each flapping stroke and varies in increments of 0.1 from Delta T-R = 0.1 to Delta T-R = 0.5 (the sinusoidal pitching case). The foil pivots about its 0.44 chord point and has a plunge amplitude of 1.05c, a phase angle between pitch and plunge of phi = 90, and a pitching amplitude of 73 degrees. All cases are run at a Reynolds Number of 10,000 and a non dimensional frequency of k = 0.8. The flow solver is Fluent v14.5, run with second order spatial discretization and first order time stepping using a dynamically layered mesh to plunge the airfoil. Grid refinement and turbulence model studies are performed. The results are compared to previously published water tunnel experiments that use direct force measurements as well as PIV to visualize the flow patterns. Overall, the effect of the side walls is small compared to the effect of the reversal fraction or kinematic parameters, however it is demonstrated that the lift on the foil is increased near the wall due to an increase of the local velocity over the foil as the wall distance decreases. However, this changes the positions of the vortices during the rest of the flapping cycle and may or may not increase the overall efficiency depending on the choice of kinematic parameters. The highest increase in efficiency occurs for the sinusoidal motion (Delta T-R = 0.5) at a wall distance of d(w) = 0.5, in which the overall power extraction efficiency increases to eta = 14.2% as compared to the free flow efficiency of eta = 11.1%, a relative increase of 28%. These trends are similar to those shown by the previously published experimental results. (C) 2017 The Authors. Published by Elsevier Ltd.