Measurement of the inter-row flow field within a transonic axial compressor using laser two-focus anemometry through curved window

When measurements are performed in high speed, small-scale compressors, the use of curved glass windows is required in order to avoid any mismatch between the measurement window and the casing. But the glass curvature leads to optical distortions, which hinder acceptable measurements and can even prevent the acquisition of any data. Thus, an original optical assembly, which consists in inserting a simple and inexpensive corrective window between the frontal lens of the anemometer and the shroud window, is proposed. The way of determining the geometric characteristics and the position of this corrective window, which restores very acceptable foci, is presented in the paper. The reliability of this corrective optical assembly is highlighted by comparative measurements in a test case. Using such an optical setting, L2F measurements have been realised along a section, downstream of the inlet guide vane (IGV) of a transonic compressor stage. The spatial resolution leads to a good description of the Interaction of the wake with the oblique shock emanating from the leading edge of the rotor. A phenomenological study of the wake/shock interaction with a change of frame is realised using the streamwise equation of the transport of vorticity.