Experimental studying the effect of water temperature on friction properties of marine propeller sliding bearing

This paper presents the effect of water’s temperature on the friction properties of materials used in marine propeller sliding bearing. Copper-Rubber and Copper-Capron, two common pairs of material in the shaft water-lubricated polymer bearing were chosen to conduct experiments with the pin-on-disc model. Various conditions including water temperature, stress, and sliding velocity were examined, their results showed that in the range 30 °C to 100 °C of water temperature, the frictional coefficient of both friction pairs were unchanged under the small stress and low sliding velocity (0.3 MPa and 0.9 m/s). While in the case of stress and sliding velocity were both high (0.6 MPa and 1.5 m/s), it increased significantly in a certain transition temperature range. This temperature range of the pair Copper-Rubber and Copper-Capron is 50 °C to 60 °C and 80 °C to 90 °C, respectively. The experiment’s results also pointed out that in these transition temperature ranges, the friction coefficient of two pairs was slightly influenced by the change in sliding velocity, whereas the stress change has an important impact on its values. Nonetheless, when the water temperature was below the transition range, the effect of the stress change on the friction coefficient was not significant. Thus, high water temperature is the main reason for the friction coefficient’s increase rather than the increase of the stress. This work is expected to broaden the understanding of the friction behavior of the water-lubricated polymer bearing.

Improved Prediction of Sheet Cavitation Inception Using Bridged Transition Sensitive Turbulence Model and Cavitation Model

Sheet cavitation inception can be influenced by laminar boundary layer flow separation under Reynolds numbers regimes with transitional flow. The lack of accurate prediction of laminar separation may lead to massive over-prediction of sheet cavitation under certain circumstances, including model scale hydrofoils and marine propellers operating at relatively low Reynolds number. For non-cavitating flows, the local correlation based transition model, γ−Reθ transition model, has been found to provide predictions of laminar separation and resulting boundary layer transition. In the present study, the predicted laminar separation using γ−Reθ transition model is bridged with a cavitation mass transfer model to improve sheet cavitation predictions on hydrofoils and model scale marine propellers. The bridged model is developed and applied to study laminar separation and sheet cavitation predictions on the NACA16012 hydrofoil under different Reynolds numbers and angles of attack. As a reference case, the open case of the PPTC VP1304 model scale marine propeller tested on an inclined shaft is studied. Lastly as an application case, the predictions of cavitation on a commercial marine propeller from Kongsberg is presented for model scale conditions. Simulations using the bridged model and the standard unbridged approach with k−ωSST turbulence model are performed using the open-source package OpenFOAM, both using the Schnerr–Sauer cavitation mass transfer model, and the respective results are compared with available experimental results. The predictions using the bridged model agree well compared to experimental measurements and show significant improvements compared to the unbridged approach.