6 - Contribution of jet–wake–volute interactions to flow characteristics and turbulence models

Abstract

This chapter deals with the study of jet–wake flow structures and their consequences as deduced from stereoscopic particle image velocimetry. Such experimental data provide the basis for spatial analysis of flow structures and their interactions. Jet–wake–volute interactions are responsible for nonuniform cyclic patterns with elevated deformations and high level of anisotropy. Transformation of strain tensor from the original coordinate into the principal coordinate shows that flow structures are dominantly planar, although the flow structures along the trailing edge of blades (wake centrelines) experience strong three-dimensional effects. Such behaviour repeats for turbulence stress tensor via calculating the extent of anisotropy by the Barycentric triangle method. The presence of significant interactions among jet–wake–volute streams not only attributes to turbomachinery performance but also complicates flow simulation. Turbulence-modelling challenges in the jet–wake flow are discussed. They include the requirement of fine-scale numerical grid for capturing sufficient turbulent kinetic energy and the deviation from classical turbulence models due to their simplifying assumption (which are not valid for turbomachinery flows).