Turbulence and Associated Production Mechanisms in an Axial Compressor Rotor Near its Stall Point

The complex structure of turbulence in an axial compressor is studied based on Stereo PIV measurement performed in a refractive index-matched facility. The analysis focuses on pre-stall conditions, when the mean flow is still stable, but the instantaneous flow is already affected by large scale intermittent fluctuations. The TKE is particularly high in regions surrounding the tip leakage vortex (TLV), and at the interface between the main passage flow and the region with low axial momentum, including region with backflow, along the tip. The high TKE around the blade tip is a statistical manifestation of spillover of large intermittent (backflow) vortices from one passage to the next in the vicinity of the blade leading-edge. The production rate terms help in identifying dominant mechanisms affecting the inhomogeneous and anisotropic distribution of Reynolds stresses. For example, near the casing, axial contraction, and shear production terms (-2〈u_θ^'u_z^'〉∂U_θ/∂z) are major contributors, whereas, near the TLV, circumferential contraction and (-2〈u_z^'u_r^'〉∂U_z/∂r) are important, while the radial contraction term changes form negative to positive values. Similar features appearing in other turbomachines highlight the prevalence of underlying flow phenomenon near the stability limit.