Blade Excitation by Broad-Band Pressure Fluctuations in a Centrifugal Compressor

Abstract

The mechanism of blade excitation during the operation of a high-mass-flow, high-pressure-ratio centrifugal compressor has been investigated. This was carried out in the compressor operating range below 60 percent of design speed and in the zone of unsteady flow occurrence, where considerable blade vibration has been measured but no periodic unsteady pressure pattern such as rotating stall could be identified. Experiments conducted to study the mechanism of interactions between flow and blades were accomplished using several measuring methods simultaneously, such as measurements of blade vibration, flow angle at impeller inlet, unsteady pressure at different meridional and peripheral locations, as well as flow visualization by means of oil pattern. Analysis of the measurements showed typical broad-band characteristics of the unsteady pressure field and also for the blade vibration behavior. Results of flow angle investigations at the impeller inlet together with the analysis of oil pattern show that the broad-band pressure fluctuations and blade excitation can be attributed to a strong reverse flow near the suction side of the radial blade in the shroud zone. This reverse flow has its source downstream of the impeller and is extending back up to a location ahead of the impeller inlet. Similar results were obtained when the compressor was operated with vaneless and vaned diffuser configurations.

Unsteady Pressure Measurements around Rotor of an Axial Flow Fan under Stable and Unstable Operating Conditions

“…At this flow rate, the component of rotating stall exists as narrowband type in the broadband frequency and the amplitude suddenly decreases. As proved in the research by Haupt et al (1) , such broadband pressure spectrum is due to reverse flow effect. In this range, the propagation speed of the stall cell and its pressure fluctuation amplitude abruptly decrease from 16.3 Hz to 8.4 Hz and the RMS value also decreases as shown in (b).…”

“…Unsteady flow phenomena such as periodic rotating stall, which is one of the most serious instabilities, and broadband pressure fluctuation (1) with non-periodic characteristics deteriorate the performance and stability of turbomachinery in vibration, noise and blade excitation. Thus, the mechanism of these unsteady phenomena is worth analyzing in the aspect of avoiding and inhibiting such instabilities.…”

Dämpfung von Rotating Stall in Radialverdichterstufen

“…12: Gasdruckschwingung und Frequenzspektrum im Radialverdichter bei r/r 2 0,85 fu È r n 10500 min -1 , u* 0,007 im Druckbetrieb fu È r vier Laufradumdrehungen von t 22,85 ms Abb. 13: Gasdruckschwingung im Radialverdichter bei r/r 2 1,20 und im Druckstutzen fu È r n 10500 min -1 , u* 0,007 im Druckbetrieb fu È r sieben Laufradumdrehungen Verdichters, wenn die Eigenfrequenz des Gasvolumens bei der Erregerfrequenz aus Rotating Stall liegt [14], [15], [16]. Bei Kenntnis der Gro Èûe der saug-und druckseitigen Speichervolumina und der Verdichterkennlinie lassen sich die Pumpzyklen und die daraus resultierenden Gasdruckschwingungen sowie die transienten Kennlinienverla Èufe berechnen [7].…”

Dämpfung von Rotating Stall in Radialverdichterstufen

“…[2], [3], [4], [5] und [6]. Es [14], [15], [16]. Bei Kenntnis der Gro Èûe der saug-und druckseitigen Speichervolumina und der Verdichterkennlinie lassen sich die Pumpzyklen und die daraus resultierenden Gasdruckschwingungen sowie die transienten Kennlinienverla Èufe berechnen [7].…”