Modern Gas turbine efficiency increase accompanied by higher turbine inlet temperature, pressure levels and rotor speeds. These demands an accurate thermal analysis of bearing compartments as large load transferred through bearings and heat load from surrounding environment. Two phase flow air &oil) is common in bearing compartments and it makes heat transfer coefficient estimation a difficult task. Bearing friction, oil churning, seals heat generations and heat input from the surroundings need to be considered accurately to predict the compartment temperatures at various operating conditions.
In addition to analysis for operating conditions, bearing compartment soak back analysis is also critical for safe operation of bearings. Absence of oil flow during shutdown of the engine can cause coking of oil film due to heat soak from the hot surroundings. Accurate soak back analysis is therefore required to simulate the thermal response of the bearing compartment during shutdown.
For the normal operating conditions, detailed numerical investigations are carried out to predict (i) optimal oil flow rate at a given rotor speed, (ii) maximum rotor speed allowed for the specified oil flow rate and (iii) the heat transfer rates for various air fractions of the oil & air mixture. The results are validated against available Engine data on scavenge oil and bearing race metal temperatures.
