Measurements of the Effects of Tunnel Wall Proximity on the Velocity Field Upstream of a Rod with Vortex Shedding in Low-Speed Flow

High cycle fatigue is an important consideration in blade design for turbomachinery. Blades in an engine undergo countless loading cycles in a lifetime, the result of pressure waves that propagate upstream and downstream from disturbances in the flow. Better understanding of these effects would allow blade designers to reduce the effects of high cycle fatigue, such as costly recurring maintenance or catastrophic engine failure. An experimental study was undertaken to determine the unsteady flow field upstream of a single cylinder in a subsonic flow. Von Karman vortex shedding from the cylinder produced a forcing function much like periodic blade passage in a turbine engine. A hot wire in constant temperature mode was used to measure the velocities upstream of the cylinder. Data were ensemble averaged and phase locked with the shedding from the cylinder to allow quasi-simultaneous comparison. The phase and amplitude of unsteady velocity data taken at a series of upstream locations were compared to a model developed from potential theory. The potential flow model for a single cylinder did not accurately predict the phase and amplitude change upstream the cylinder except when the cylinder was near the center of the tunnel. When virtual cylinders were added to account for endwall reflection, the prediction more closely approximated the behavior of the data. While much is yet to be understood, the results of this study indicate that the flow field upstream of a disturbance may be reasonably predicted using elements of potential flow theory.Air Force Inst of Tech Wright-Patterson AFB Oh School of Engineering is the author of 'Measurements of the Effects of Tunnel Wall Proximity on the Velocity Field Upstream of a Rod with Vortex Shedding in Low-Speed Flow', published 2000 under ISBN 9781423536499 and ISBN 1423536495.