The conditions of film formation and of film separation are examined experimentally and theoretically in a line Hertzian contact when the inlet region is partially filled with oil, in steady state hydrodynamic regime, for both rolling and sliding conditions. It is shown experimentally that the importance of the parameter μU/T (viscosity and speed/surface tension) differs at inlet and exit. At contact exit the influence of μU/T is dominant and the film divides to form a meniscus which can be stable or unstable. The validity of the Coyne and Elrod model is confirmed. At contact inlet when reverse flow disappears, a meniscus is also formed with a downstream circulation zone. The instability of the exit air-oil meniscus is studied theoretically using the linearized perturbation method with the thin film assumptions. A simple and complete analytical solution yields both a stability criterion and the wave number for the linear contact geometry. These results which are compared with experiments for thin film and for 0.01 < μU/T < 1 show the validity of the stability criterion and that best agreement is obtained with the wave number of maximum amplification.

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