An Inquiry of the Friction Factor “Jumpâ€‌ Phenomenon in Hole Pattern Seals

Abstract

Experiments measuring the leakage rate through holepattern seals operating at high pressures of up to 8400 kPa reveal the presence of an abrupt variation in the friction factor (up to a factor of three) with change in the pressure difference across the seal. The measured pressure fluctuations suggest that this observation may, perhaps, be understood as a change in fluid instability modes across the cavities of the seal. A more detailed investigation via large eddy simulations (LES) suggest that the switching from shear layer instability mode to a wake instability mode, a phenomenon well known in fundamental studies of cavity flow (without a top bounding wall), is responsible for the observed variation.