The Effect of Casing Grooves on the Turbulence in an Axial Compressor Near its Best Efficiency Point

Stereo-PIV measurements performed in a refractive index matched facility examine the effect of axial casing grooves (ACGs) on the flow and turbulence within a one and a half stage axial compressor near its best efficiency point. These grooves are installed to delay the onset of stall but often cause efficiency penalty at design flow rates. Data are acquired at multiple axial planes, within and between the blade rows spanning the entire machine. The data are used for calculating the ensembled-averaged turbulent kinetic energy (TKE), Reynolds stresses, and associated production rate terms. Without ACGs, the turbulence in the tip region is affected by the tip leakage flow, blade wakes, as well global radial and circumferential contraction and extension throughout the machine. With the grooves installed, the flow jetting out of the ACGs upstream of the rotor leading edge rolls up into axially aligned vortices, which interact with the tip region flow. Driven by shear production, these vortices cause a significant increase in TKE along the periphery and downstream of the rotor. However, the differences between turbulence levels near the treated and untreated endwalls diminish as the flow passes through the stator downstream of the rotor.