Review of long steam turbine blade packet resonance

"Interference Diagrams” also termed by some as “Safe Diagrams" are utilized for fully-coupled rotating blades. In Reference No. 1 resonance where harmonic of speed is equal to nodal diameters is reviewed, along with when difference in numbers of blades and vanes equal to number of diameters.

Mistuning of steam turbine blade packets

There are many steam turbine rotor stages with blades connected together for added reliability, making them much more difficult to excite from alternating forces such as upstream vane wakes and potential flow effects such as partial admission. Procedures are described to be sure a "safe" design considers variations giving mistuned resonant response factors.

Can High Noise Levels Cause Fatigue Of Covered Impellers?

As shown in previous articles it is stationary vane numbers that can cause significant interaction resonance of disk modes. Direct pressure loads at rotating blade passing frequency and harmonics in turn excite stationary vane natural frequencies. Downstream diffuser vanes for compressor stages are of prime importance to consider for resonance avoidance with number of rotating blades times speed. But there is some confusion in that some investigators have said to also avoid direct resonance where rotating blade passing frequency is equal to a disk mode frequency.

Bladed Disk Resonance - Part 3 - Open Impellers

Covered impellers are predominately used in process gas compressors with high loading per stage. Mechanical tip speeds can be fairly low especially for high mol weight gases than give high equivalent aerodynamic tip speeds. Use of a cover disk however limits tip speed possible for some designs; open impellers prevail for applications such as plant air compressors and turbochargers, including radial turbines. Centrifugal stress limits determine if a cover can be used; however as long as possible resonance points, some of which are described below, are evaluated the cover can be eliminated.

Bladed Disk Resonance - Part 3 - Open Impellers

Covered impellers are predominately used in process gas compressors with high loading per stage. Mechanical tip speeds can be fairly low especially for high mol weight gases than give high equivalent aerodynamic tip speeds. Use of a cover disk however limits tip speed possible for some designs; open impellers prevail for applications such as plant air compressors and turbochargers, including radial turbines. Centrifugal stress limits determine if a cover can be used; however as long as possible resonance points, some of which are described below, are evaluated the cover can be eliminated.

Disk Resonance Equations & Interference Diagrams

A 2-diameter mode shape for a covered impeller is shown below. Two areas vibrate in phase while two other areas are simultaneously out-of-phase.

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Blade / Vane Interaction Resonance Of Rotating Disks

As this is my initial submission on Dynamics & Acoustics, I should start with aspects of Wilfred Campbell’s “Campbell Diagrams”, Ref. [1].

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