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Item type:Publication, Access status: with files , Direct numerical simulation of the centrifugal instability-induced transition around a marine propeller blade(Norwegian University of Science and Technology, Department of Marine Technology, 2024-04-04); The boundary layer regime knowledge is a key factor in predicting the performance of lab-scale marine propellers. Even if the distribution of the boundary layer flow regime around the propeller blade is well-known by the marine propeller community, no dynamic of the turbulent process has already been reported in the literature. An Underresolved Direct Numerical Simulation (U-DNS) of a Cseries marine propeller blade at a Reynolds number of 600, 000 and an advance coefficient of 0.73 is performed to gain insights into the turbulent transition mechanisms of the boundary layer. An overset approach is used with the open-source spectral element code Nek5000 to optimize the computational cost of the simulation. After performing a mesh-sensitivity analysis, results are validated using experimental data. The detailed investigation of the boundary layer shows good agreement with the experimental and numerical data. New insights into the turbulent transition dynamics suggest that centrifugal instability plays a major role in the transition process. A map of the boundary layer flow regimes is then discussed. The laminar cross-flow vortices’ inception and breakdown are studied in detail to characterize the onset of longitudinal streaks.Publicationtype: Conference Paper21 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental study on dynamic forced pitch motions of rigid and flexible hydrofoils in towing tank(Norwegian University of Science and Technology, Department of Marine Technology, 2024-04-04); ; ; ; This paper presents a study on the hydrodynamics of rigid and flexible hydrofoils, in dynamic stall regime due to pitching actuation. An original experimental setup was developed to accommodate large scale innovative appendages, in the towing tank at Centrale Nantes, France. The original feature of the setup is its capability to simultaneously induce dynamical pitching motions to the appendages, and use optical fibers with arrays of fiber bragg gratings, for real-time strain monitoring. Forces and moments are measured dynamically with a six degreeof-freedom hydrodynamic balance. In this study, the Reynolds number considered ranged from Re = 160 000 to 1 000 000. The appendages are pitch-actuated with reduced frequencies k = πf c/V up to 0.14. Two appendages are considered. The first one is a rigid, thick, rectangular hydrofoil with a low aspect ratio (rudder-like hydrofoil). The second one is a flexible, thin, trapezoidal hydrofoil with a high aspect ratio (simplified propeller blade geometry). The data demonstrated setup capabilities to capture subtle flow phenomena such as as displacement of center of pressure, or delay of stall onset. Finally, the measurements present very good correlation between measured lift coefficients and strains of the flexible hydrofoil.Publicationtype: Conference Paper23 106