Coupling of Unsteady Lift to Acoustic Duct Modes in an Axial Flow Fan.
Abstract
By using distortion screens, plane (0,0) and spinning (-1,0) acoustic modes were generated in an axial flow research fan. The unsteady lift on the rotor blade and the acoustic pressure along the duct were measured simultaneously by a lift gage sensor and a flush-mounted microphone respectively. The screens were calibrated by circumferentially traversing a five-hole probe. The typical background noise of unsteady lift and acoustic pressure was well below the desired signals. A phase-locked ensemble averaging technique was used to obtain the amplitude and phase of the periodic unsteady signals. The measured acoustic pressures were decomposed into modal pressures and compared with theoretical prediction; a reasonable trend was reached, but the discrepancies were large. The unsteady lift measurements of (-1,0) mode generation agreed with predictions except near the cutoff frequency indicating a back-reaction effect of considerable magnitude. The predictions overestimated the unsteady lift for the condition of 'aerodynamic resonance' when the plane wave was generated. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 15, 1980
- Accession Number
- ADA095080
Entities
People
- C. S. Lee
Organizations
- Pennsylvania State University