Cavitation estimates by orbit prediction of a journal bearing – Finite element modelling and experimental studies
The paper presents a two-sided approach to establish understanding of the cavitation phenomenon in dynamically loaded journal bearings, more specifically the engine bearings of large two-stroke marine diesel engines. One disadvantage of the journal bearing is the converging-diverging geometry making it prone to cavitation which again affects the load carrying capacity of the bearing. In combustion engines the journal bearing plays a vital role especially as main and crosshead bearings transmitting the combustion forces. Those forces vary highly during one combustion cycle which is further influencing the load carrying capacity and ultimately the chances of fatal shaft-sleeve contact. By solving Reynolds equation numerically using finite elements and incorporating a cavitation algorithm, the dynamic coefficients can be used to establish the journal orbit for a given bearing and load pattern. Validation of the results is done against the Ruston and Hornsby 6VEB-X Mk III engine. Besides the numerical investigations a cavitation test rig has been developed. With this rig it is possible to generate cavitation under controlled conditions in terms of load/eccentricity and rotational speed. The development of cavitation in time in terms of position and distribution can be visually recorded.