Some Canonical Examples of Streamwise Vortex Structure for Rotating Components

Nose cones, turbine blades and bearings have rotating components and represent very practical geometries for which the modal behavior of vortex structures is not completely understood. These three rather different physical cases are being studied. A common theme of competition between modes and vortex types, whether counter-rotating or co-rotating, emerges. The objective of ongoing work is to obtain physical confirmation, enhanced understanding and predictive capability for the vortex structures encountered in rotating machines. INTRODUCTION Stable vortex structures have been observed in a range of flows of industrial relevance, such as flows over conical aerodynamic fairings, turbine blades with cylindrical leading edges and between co-axial cylinders. The persistence of the vortical structures, over a defined duty or flight envelope appears to be a common theme among these applications. Investigations of experimental results over the envelope of geometrical and flow parameters have guided the ___________________ * Corresponding author. development of predictive methods for these structures, based on asymptotic perturbation methods of inviscid baseline flow models. Three examples of flows generating vortical structures indicate a possible common driver, involving stationary streamwise vorticity. This encourages the development of the current models to give a generalized representation for this class of flows. SURFACE FLOWS OVER ROTATING CONES Evidence for the existence of a hitherto unidentified instability mode in boundary-layer flows over rotating cones exists in the literature. This new mode is in addition to the crossflow (type I) and streamline curvature (type II) modes that are already known to exist [1] on rotating cones, disks and spheres. It is important to realize that throughout this paper the word mode refers to a physical mechanism rather than a spatial entity. Evidence set 1: experimental observations The visualization studies by Kobayahsi and co-workers [2, 3] of rotating cones with slender half-angles show the existence of pairs of counter-rotating Görtler-type vortices prior to the appearance of turbulence. However, as the half-angle ψ is increased beyond 40 ◦ , the visualizations clearly show that these vortices change to Proceedings of the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting FEDSM2014 August 3-7, 2014, Chicago, Illinois, USA