Effect of In-Line Tandem Configuration on Performance and Scaling of Pitching Hydrofoils

Simulations are reported on the behavior of two tandem symmetric foils in an in-line configuration undergoing pitching motion. The Reynolds number was varied between 1000 and 4000, whereas the pitching Strouhal number ranged from 0.2 to 0.5 and the amplitude of pitching varied from 4 to 8 deg. The streamwise separation distance between the foils was fixed at one chord length. The performance of the downstream foil was significantly worsened (up to 80% in efficiency) by the tandem effects. The Strouhal number, Reynolds number, and pitching amplitude had substantial impact on the performance of the downstream foil. For the upstream foil, however, the performance improved by up to 147% in efficiency at all ranges of Reynolds number, Strouhal number, and pitching amplitude. The scaling of the individual foil performance metric and the system collective performance metric were investigated for tandem foils. The scaling developed for isolated foils does hold for tandem foils in the in-line configuration with modified empirical coefficients that depend on reduced frequency and Reynolds number in a range of St and Re. However, the leading foil behavior at lower St is more scattered compared to higher St, which suggests more significant wake interactions that influence the scaling and performance of the leading foil.Canada First in Research Excellence through the University of Alberta Future Energy Systems Institute [T14-Q01]This study has received support from Canada First in Research Excellence through the University of Alberta Future Energy Systems Institute, grant number T14-Q01. The simulations were carried out using the Compute Canada computational clusters