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Early-Stage Investigation of Environmentally Friendly Sliding Bearings for Offshore Wind Turbine Main Shafts

Wasilczuk Filip, Wasilczuk Michał, Flaszyński Paweł, Litwin Wojciech

Polish Maritime Research

2025

nr 4

157--167

This work presents a preliminary assessment of the potential application of water-lubricated radial sliding bearings as main shaft bearings in large offshore wind turbines. The study is driven by the environmental concerns and the high cost and size associated with conventional rolling element bearings. Four bearing material candidates were examined: lignum vitae, a compliant elastic polymer, a three-layer PTFE-based composite, and a fibre-reinforced polymer. Pilot experiments were carried out on a custom-built test rig capable of accurately capturing friction torque under controlled radial loads, with freshwater serving as both lubricant and coolant. The procedure included a defined running-in phase and multiple repeated tests to ensure reproducibility. The sliding speed and load conditions were determined using a combination of multi-body dynamic simulations of the IEA 15 MW reference turbine and published load analyses, ensuring that the test conditions reflect realistic operating values. The results showed that the polymer and PTFE-based composite exhibited excellent tribological behaviour, maintaining very low friction coefficients during both steady and start-up operation. Although the wear behaviour was not quantified at this stage, the low friction coefficients indicate operation in a full hydrodynamic lubrication regime, which is expected to minimise wear. Overall, this preliminary investigation suggests that selected water-lubricated sliding bearings represent a promising, environmentally friendly alternative for offshore wind turbine main shafts, offering advantages in corrosion resistance, durability under dynamic loading, and potentially low wear.

Test section design for measuring the drag coefficient of a suborbital rocket model at Ma 2.45

Wasilczuk Filip, Kurowski Marcin, Flaszyński Paweł

Transactions on Aerospace Research

2024

Nr 3 (276)

86--100

This study investigates the drag coefficient of three models of suborbital rockets with different nosecones. A test section allowing for force measurement of a 1:50 scale rocket model was designed with the aid of numerical simulations. The velocity obtained in the wind tunnel corresponds with a Mach number of 2.45. RANS simulations were used in verifying operating parameters, as well as testing the support configurations for connecting the model with the bottom wall of the tunnel section. Pressure distribution measurements on the top and bottom walls of the wind tunnel matched simulation results well. The shock structure in the test section was visualized using the schlieren technique, revealing that the measured angle of the main shock generated at the tip of the rocket matched the simulation data. Finally, the measured forces were compared with simulations for one of the nosecone configurations. Despite very good agreement for pressure distribution on the wind tunnel walls and shock structure, a significant mismatch in the forces measured was nevertheless observed: the simulated CD (0.57) being four times larger than that obtained in measurements (0.138). Further analysis of the test section is required to pinpoint the source of discrepancies and redesign the force measurement system to achieve improved force results.