An experimental study of boundary-layer transition induced vibrations on a hydrofoil

Abstract

International audienceThis paper aims at characterizing experimentally laminar to turbulent transition induced vibrations. Here, the transition is known to be triggered by a Laminar Separation Bubble that results from a laminar separation of the boundary-layer flow on a hydrofoil. In this study we consider two NACA66312 (Mod) laminar hydrofoils at low angles of incidence (mostly 2° and 4°) and Reynolds numbers ranging from Re=450 000 to 1 200 000, in order to get transitional regimes. The first hydrofoil, made of steel (E=2.1×1011 Pa), is referred to as the rigid hydrofoil, although it is seen to vibrate under the action of the LSB. To better understand the possible interaction between the flow and the foil vibrations, vibration measurements are repeated using a flexible hydrofoil (E=3×109 Pa) of same geometry (under zero loading) and in close configurations. The experiments are carried out at the French Naval Academy Research Institute (IRENav, France). Wall pressure and flow velocity measurements enable a characterization of the laminar separation bubble and the identification of a vortex shedding at a given frequency. It is hence shown that the boundary-layer transition induces important foil vibrations, whose characteristics in terms of frequency and amplitude depend on the vortex shedding frequency, and can be coupled with natural frequencies of the hydrofoils

Experimental study of the steady fluid–structure interaction of flexible hydrofoils

“…The lack of agreement between the estimated first mode for the Type II-CFRP30 and the measured response under hydrodynamic loading suggests a more complex behavior for this hydrofoil. As discussed below this hydrofoil exhibits a significant coupled bend-twist deformation, suggesting that the measured response is not due to bending alone but a coupled mode due possibly to an FSI response (Ducoin et al, 2012a).…”

Effect of the laminar separation bubble induced transition on the hydrodynamic performance of a hydrofoil

“…his section aims at providing local validation to complete the global validation based on force coefficients. This way, velocity profiles in the vicinity of the LSB at AoA = 2°are compared to experimental data from Ducoin et al [21] (Fig. 12).…”

Experimental investigation of added mass effects on a hydrofoil under cavitation conditions

“…In the field of hydraulic machinery, fluid-structure interaction (FSI) phenomena involving hydrofoils are a major concern, and several investigations have been performed on this topic. Ducoin et al (2010a) experimentally studied the vibrations induced in a hydrofoil by the laminar to turbulent boundary layer transition and determined their significance and dependence on the vortex shedding frequency. Olofsson (1996) experimentally studied the dynamic performance of partially submerged propellers.…”