Local and Mean Heat Transfer Coefficients Along the Internal Housing Walls of Aero Engine Bearing Chambers

Abstract

A proper matching of the heat transfer to the lubrication oil in bearing chambers and subsequent vent and scavenge pipes is one of the major tasks in the design process of secondary air/lubrication oil systems of modern jet engines. For a calculation of lubrication oil flow rates, which should be kept as small as possible in order to reduce parasitic losses due to larger pumps, filters and coolers, a sufficient knowledge of all heat transfer phenomena involved in bearing chamber flows is required. Beside heat sources such as the bearing friction, the heated sealing air flow and the churning and ventilation of two-phase mixtures, the heat transfer at the housing walls has to be considered. The present paper deals with an experimental investigation of the latter effect based on engine relevant pressure and temperature levels bearing chamber operating conditions. Air/oil flow heat transfer measurements at the internal bearing chamber walls are described utilizing the temperature gradient method. It is a stationary technique based on a two-dimensional finite element calculation procedure. Influences of sealing air flow rate, lubrication oil flow rate and rotational speed on local heat transfer coefficients are discussed. Mean heat transfer coefficients that have been calculated from local data are presented in terms of operational parameters.