Abstract
As part of an ongoing investigation into the mitigation of vortex induced vibrations of hydrofoils, a combined experimental and numerical study of the fluid-structure interactions and wake of a hydrofoil at lock-in has been conducted at the Waterpower laboratory of the Norwegian University of Science and Technology. The hydrofoil has a blunt trailing edge and Von Karman vortex shedding induces a lock-in effect at a chord based Reynolds number of about 2,7e6. The present paper presents the initial measurements of vortex shedding frequencies going through lock-in, along with CFD simulations at lock-off conditions as well as some empirical estimates of vortex shedding. Experimentally the hydrofoil wake was studied in detail using particle image velocimetry (PIV). Hydrofoil vibration frequencies were measured by both a strain gauge positioned near the trailing edge of the foil as well as by a laser doppler vibrometer (LD-V). Numerically the phenomena was simulated using ANSYS CFX. Several different turbulence models was tested, from the two-equation standard k−epsilon model to the scale adaptive SST-SAS model, with considerably different results. It is observed that the vibrations induced at lock-in considerably shifts and reduces the hydrofoil wake velocity deficit. Further,the CFD results suggest that the driving parameter influencing the shedding frequency is the cross flow separation distance at the trailing edge.
