Cooling of bearing chamber walls is achieved by the through-flow of thin oil films, which are typically only a few millimeters thick. Support structures and other features disrupt both air and oil motion within such chambers, leading to localized variations in the oil film thickness, which in turn cause variation in local heat transfer coefficients. In extreme cases, the presence of wall protrusions may result in complete “dry-out” or thickening of the wall film. This paper describes an experimental study that has been undertaken to establish the range of conditions under which shear driven liquid films dry-out upstream and downstream of different obstacles. Three different sizes (0.5”, 1” & 1.5”) of cylindrical and square obstructions were employed. The effect of obstacle shape, size and orientation has been investigated. The interactions of waves and dry-out patches has also been investigated, as has the dependence on previous states (i.e. the liquid flow rate and the whether the surface was previously wetted). A number of conclusions have been drawn that provide a starting point for designers in specifying obstruction shapes that are less likely to cause film dry-out for obstacles that protrude through film flows.

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