Abstract:
This thesis presents an experimental investigation into the conditions
generated within a high speed bearing system where thermally generated
shaft bows can arise from differential journal heating, and under certain
condtions this effect has been observed to result in unstable shaft vibration -
the ‘Morton Effect’. This thesis documents the development of a simplified
analytical procedure for evaluating the thermal activity within an orbiting
journal when running in hydrodynamic bearings. The aim of this work was to
generate controlled experimental data regarding journal differential heating
effects to support the understanding and development of appropriate
modelling and predictive techniques.
A high speed rotor test rig, running in 50mm diameter bearings of fixed and
variable geometry configuration, was used to obtain directly measured
temperature distributions within the rotor when running under varying speed
and unbalance response conditions.
Two separate rotor designs were used. The first is designed as a rigid rotor
where no structurally influenced rotor dynamic phenomena are present within
the running ranges. The second is a flexible rotor designed to operate in a
super critical condition where conditions are replicated to provide a rotor that
is sensitive to the variables required for thermal bow development and the
rotordyanmic conditions promotional of associated instabilities. Existing
theoretical models, in combination with operationally observed characteristics,
were used to develop a design predicted to become unstable within the test
running range.
Journal temperature measurements were obtained for rigid and flexible rotors
over a range of speed conditions in intentionally introduced mechanical
unbalance conditions. Journal temperature differentials were obtained with a
clear correlation between journal orbit size and journal temperature
differential. The flexible rotor was operated for prolonged periods of time in
the predicted unstable region but instability was never initiated for any test
condition. Peak journal temperature differentials were measured as 1.7 oC.
A new analytical model for the bearing oil film and journal thermal
developments is presented which has reasonable correlation to other
published literature.