Stereoscopic PIV measurements in a two-stage axial turbine

Abstract

In the present work, the three-dimensional flow field in the interstage region of a twostage axial turbine has been measured by a stereoscopic PIV system. The stereoscopic method is used to compensate for perspective as well as to observe the highly threedimensional flows. The digital images are recorded with a set of two cameras positioned perpendicularly to the measurement plane and inclined by an angle varying between 22° and 30° to allow stereoscopic measurements. The laser beam is delivered to a laser endoscope able to access the measurement areas. By traversing radially, several blade-to-blade planes can be illuminated with the laser endoscope from 66 to 96% blade span. To compensate for the perspective distortion of the field of view due to the tilt angle of camera B as well as the optical distortion through the double-curvature windows, a threedimensional calibration method is used. In the current investigation, a Monte Carlo simulation has been conducted to evaluate measurement errors of PIV. Results of these measurements are compared with velocities derived from time resolved pressure measurements using fast aerodynamic response probe (FRAP). A good agreement is found at the exit of the second rotor. The present work present a unique set of steady and unsteady data measured in a two-stage axial turbine. Measured data in a volume can be used for numerical tool validation as well as improve existing kinematic model of vortex transport and dissipation.