Using the recommendations above would give more reasonable evaluations. Another consideration for the next revision of API is to change locations of unbalance for unbalance response analyses:. Unbalance shall analytically be placed at the locations that have been determined by the undamped analysis to affect the particular mode most adversely.
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For the translatory symmetric modes, the unbalance shall be based on the sum of the journal static loads and shall be applied at the location of maximum displacement. For conical asymmetric modes, an unbalance shall be added at the location of maximum displacement nearest to each journal bearing. These unbalances shall be degrees out of phase and of a magnitude based on the static load on the adjacent bearing. Unbalance shall analytically be placed at the locations that are most likely to occur to affect the particular mode most adversely.
For the translatory symmetric modes, the unbalance shall be based on the sum of the journal static loads and shall be distributed in phase along all the stages in the compressor or turbine. For conical asymmetric modes, an unbalance shall be added at the location of major elements at the ends of the rotor. A third case would be with unbalance at the coupling s for use in unbalance response tests during mechanical testing. Frank Kushner is an independent Consulting Engineer specializing in dynamics and acoustics testing and analysis. Kushner holds patents for a blade damping mechanism and a method to prevent a one-cell rotating stall in centrifugal compressors.
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Forgot Password? View Cart Checkout. Compressors , Gas Turbines , Steam Turbines Are shaft vibration and unbalance limits too stringent for some rotors?
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Rotors balanced in low speed balance machines have low maximum limits, especially for low speed designs with heavy rotors. Unbalance distribution should be better allocated along the rotor for unbalance response calculations.
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Another consideration for the next revision of API is to change locations of unbalance for unbalance response analyses: Instead of: SP6. References: 1. Frank Kushner.
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Turbomachine Sealing and Secondary Flows. Lockheed Martin Space Systems Co. Consulting, Minden, NV, United States Abstract: Today's computational methods enable the determination of forces in complex systems, but without field validation data, or feedback, there is a high risk of failure when the design envelope is challenged. The data of Childs and Bently and field data reported in NASA Conference Proceedings serve as sources of design information for the development of these computational codes.
Over time all turbomachines degrade and instabilities often develop, requiring responsible, accurate, turbomachine diagnostics with proper decisions to prevent failures. Tam et al. The stability threshold can be controlled by external swirl and swirl brakes and increases in radial fluid film stiffness e.