Browse Publications Technical Papers 2023-01-1006
2023-03-07

Unbalance Budgeting Optimizes Rotor Design for Assembly Performance - Straight, Balanced Rotors Run Smoother! (2023-01-1006) 2023-01-1006

In rotor engineering, one must achieve a rotor design incorporating a well-controlled state of unbalance. A reduced nominal rotor unbalance assures achieving permissible vibration responses during measurement.
Geometric feature controls associated with manufacturing drawings are root causes of vibratory measurements during engine testing. Difficulties arise during component design using software that fails to account for the presence of unbalance, or the ability to achieve a balanced state for each rotor design. Manufacturing procedures ensure that serial production articles are within tolerance limits established by the manufacturing drawings. This process is intended to ensure unbalance contributions estimated during the design phase will permit vibration limits to be met during final acceptance test.
Performance of a rigid rotor under test cell conditions is dependent upon effective control of runout and eccentricity between mating components. Establishment of these tolerances must be accommodated in the design to ensure which tolerance limits, and the resulting stacked tolerances are acceptable to achieve established vibration limits during a final acceptance test. Otherwise, this results in misalignment of the mass axis relative to its bearing journals.
Using finite element methods, we can estimate the impact of several unbalance distributions along the rotor axis and its excitation of rotor shaft-elastic behavior. Predictive analyses with probabilities determine contributions toward assembly vibration levels. We propose a method to account for the impact of permissible manufacturing uncertainties during the earliest stages of rotor design upon subsequent assembly processes. 

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