Experimental Characterization of Darcy Friction Factors of Bump Channel Flows and Application to Cooling Flow Path Design

Foil bearings are considered the most promising oil-free bearing technology for small high-speed turbomachines. Among many different underlying supporting structures, corrugated bump foils are the most popular. Due to the geometry of corrugation, the bump foils have gas flow passages through the bump channels, and cooling gas is introduced through these bump channels. The flow resistance through these bump channels is a function of bump geometry, ambient conditions, and type of gases. When multiple foil bearings are installed within a system, cooling gas flow passage design through the bearings requires proper understanding of bump channel flow resistances. Inadequate cavity pressures arising from the cooling gas flow passage design can create undesirable axial force to the thrust bearings. This paper presents experimentally measured Darcy friction factors of typical bump channels in both laminar and turbulent flow conditions, as a function of flow Reynolds number and hydraulic diameter determined from the bump channel geometry. This paper also presents experimentally measured flow characteristics of radial and thrust foil bearings, and measured results are compared with the prediction using the experimentally extracted Darcy friction factors.