An improved wake description by higher order velocity statistical moments for single screw vessel. (1st November 2015)

• Record Type: Journal Article
• Authors: Pecoraro, Andrea; Di Felice, Fabio; Felli, Mario; Salvatore, Francesco; Viviani, Michele
• Is Part Of: Ocean engineering. Volume 108(2015)
• Page Start: 181
• Page End: 190
• Publication Date: 2015-11-01
• Subjects: Ship and propeller wake -- LDV -- Propeller–hull interaction -- Flow separation; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2015.07.038
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: 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 minimize fuel consumption and avoid excessive vibratory shaft loads and risk for cavitation erosion. 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 context, the study also concerned 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. Highlights: Propeller suction on the flow is observed upstream to a distance of 1 prop radius. Blade induced velocity fluctuations extends upstream to 0.4 prop radius. Prop reduces the detached volume size but don't remove totally the flow separation. The flow separation boundary is identified by the velocity skewness coefficient. The "mode" wake is a more robust description of the propeller inflow.