Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Low Engine Order Forcing Effects

Current developments in Forced Response (including the previous programme: ADTurB) focus on vibration modes excited at wake passing frequency. Low Engine Order (LEO) excitation is caused by small differences in the flow around the annulus. It is therefore much more difficult to predict because it depends upon knowledge of the sources of the variation and sensitivity of the vibration response to these small changes. For vibration at wake passing frequency it is possible to model a small number of aerofoil passages because the flow distortion is assumed to be identical for all nozzle guide vanes. An analysis method for low engine order forced response would typically need to model the whole annulus and explicitly include the vane-to-vane variation that would be representative of a real machine.

Unique experiments were undertaken utilising a slightly modified existing research rotor and a continuous flow rig facility at DLR to include:
- Vane to vane throat width variation in the set.
- Variability in cooling flow ejection between vanes in set,
- blockage simulation.

Data gathered included detailed measurements of the flow field under LEO conditions using pressure transducers & Laser 2 Focus device. Each blades amplitude was recorded simultaneously via strain gauges. Supporting Aeroelastic analysis was carried out for correlation with fluid & response measurements. It is expected that by improved understanding of the excitation sources & validation of prediction tools significant reductions can be made in HCF events related to LEO.

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