An improved wake description by higher order velocity statistical moments for single screw vessel

Unfavorable wake and separated flow from the hull might cause a dramatic decay of the propeller performance in single-screw propelled vessels such as tankers, bulk carriers and containers. For these types of vessels, special attention has to be paid to the design of the stern region, the occurrence of a good flow towards the propeller and rudder being necessary to avoid separation and unsteady loads on the propeller blades and, thus, to minimize fuel consumption and the risk for cavitation erosion and vibrations. The present work deals with the analysis of the propeller inflow in a single-screw chemical tanker vessel affected by massive flow separation in the stern region. Detailed flow measurements by Laser Doppler Velocimetry (LDV) were performed in the propeller region at model scale, in the large Circulating Water Channel of CNR-INSEAN. These tests were undertaken with and without the propeller in order to investigate its effect on the inflow characteristics and the separation mechanisms. In this regard, the study concerned also a phase locked analysis of the propeller perturbation at different distances upstream of the propulsor. The study shows the effectiveness of the 3rd order statistical moment (i.e. skewness) for describing the topology of the wake and accurately identifying the portion affected by the detached flow. The skewness coefficient also suggests that a better physical representation of the propeller inflow is provided by the mode value of the velocity, which is the maximum of the probability density function, rather than the mean velocity.