The Flettner rotor is attracting increasing attention as a viable technology for wind-assisted ship propulsion. Nonetheless, the influence of the Reynolds number on the aerodynamic performance of rotating cylinders is still unclear and under debate. The present study deals with a series of wind-tunnel experiments on a large-scale Flettner rotor in which the forces and pressures acting on the cylinder were measured for Reynolds numbers as large as Re=1.0⋅10 ⁶ . The rotating cylinder used in the experimental campaign had a diameter of 1.0 m and span of 3.73 m. The results indicate that the lift coefficient is only affected by the Reynolds number in the critical flow region and below velocity ratio k=2.5. Conversely, in the velocity ratio range 1<k≤2.5, the drag coefficient is markedly influenced by the Reynolds number over the entire range of flow conditions analyzed. The power coefficient scales with the cube of the tangential velocity and it appears to be insensitive to the Reynolds number or whether the cylinder is spun in an air stream or in still air.

Experiments on a large-scale Flettner rotor were carried out in the boundary-layer test section of Politecnico di Milano wind tunnel. The rotating cylinder used in the experimental campaign (referred to as Delft Rotor) had a diameter of 1.0 m and span of 3.73 m. The Delft Rotor was equipped with two purpose-built force balances and two different systems to measure the pressure on the rotor’s outer skin. The goal of the experiments was to study the influence of different Reynolds numbers on the aerodynamic forces generated by the spinning cylinder. The highest Reynolds number achieved during the experiments was.

The present study describes the application of the particle image velocimetry (PIV) technique for the reconstruction of hydrodynamic pressures and loads on a ship model from measured velocity fields during towing tank tests. As an alternative to conventional pressure and force measurement techniques the method simultaneously pictures the velocity field and captures the dynamic aspect of the flow. The presented measurements are conducted in the transom region of a generic hull of a planing vessel which is equipped with an interceptor to create a stagnating flow, associated with a high pressure peak. The flow close to the hull is captured with an underwater stereoscopic PIV system and the pressure peak in front of the interceptor is reconstructed from time-averaged velocity fields. Results show the effect of different interceptor heights on the pressure distribution in the center-plane of the model. Further, a 3D flow field is reconstructed from scanning PIV measurements to analyze the lift reduction due to the finite span of the interceptor. The spatial variation of the measurement uncertainty is analyzed and propagated to the pressure field uncertainty and the potential of the method is further evaluated by comparison with numerical results from steady Reynolds Averaged Navier-Stokes (RANS) simulations.

The workability of various types of operations offshore are largely affected by waves and wave induced motions. Examples are crew transfer from crew transfer vessels or service operation vessels to offshore wind turbines for maintenance, landing of helicopters in (navy) vessels and various crane operations. Over the recent years quite some effort has been put in technology aiming to provide a real time on-board prediction of approaching waves and wave induced vessel motions some minutes in advance. Enabling crew to anticipate, thus enhancing the safety and operability of these operations. This paper addresses the performance during a field test of the system as being under development by Next Ocean enabling such predictions, based on using an off-the-shelve (noncoherent) navigation radar system as a remote wave observer. Briefly summarizing (earlier publications on) the technical approach, focus will be on results obtained from a field test where the system was validated. Good agreements between ship motions as measured by an on-board motion reference unit and predictions obtained by the wave and motion prediction system during a field test on the North Sea near the Dutch coast on a 42 m patrol vessel will be shown in the results section, from which the usefulness of the system for operational decision support can be concluded.