Analytical and Experimental Study of Subsonic Stalled Flutter.
Abstract
A series of experimental measurements of airfoil pressure distributions were made in an eleven-airfoil oscillating cascade wind tunnel. The airfoils were oscillated in pitch about mid-cord pivots with an amplitude of + or - 2 degrees at tunnel velocities of 100, 150 and 200 feet-per-second, obtaining reduced frequencies in the range of 0.03 to 0.20. Incident air angles were set at 12, 10 and 8 deg; the cascade angle was 30 deg from a fully closed setting; tests were run at interblade phase angles of zero and forty five degrees. A computer program was adapted to calculate oscillating lift and moment coefficients on the assumptions of incompressible flow, flat plate airfoils, fixed separation point, zero pressure amplitude in the separated region and in the wake, and all streamlines parallel to the airfoil surfaces. The calculations were found to give good agreement between theory and experiment for assumptions of separation at 75 percent chord for 45 degree interblade phase and at 85 percent chord at zero phase, independent of reduced frequency and air inlet angle. At 12 deg air inlet angle, the experimental appearance of large effects at twice the oscillation frequency prevented application of the theoretical analysis. The calculated values at zero phase are limits as approached by very small negative phase angles, and differ substantially from calculated values approached from the positive side. The reasons for this discrepancy are not known. It is recommended that experimental studies be aimed at a range of moderate phase angles, both positive and negative.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1976
- Accession Number
- ADA027869
Entities
People
- A. St. Hilaire
- F. O. Carta
- R-h. Ni
- R. A. Arnoldi
Organizations
- Pratt & Whitney