Compressibility Effect in Vortex Identification

Abstract

F LOW problems of aircraft, missile dynamics, high-speed transportation, compressible slenderand bluff-body wakes, wingtip vortices, aerodynamics of rotors, propellers and blades, environmental flows, and local meteorology are some examples of aerodynamic problems frequently dominated by vortical structures. Understanding of vortices and vortex dynamics in such flows is of primary interest. Flow modeling is steadily forced to improve the analysis of the given aerodynamic problems and the accuracy of compressible-flow prediction. A considerable number of vortexidentification methods, vortex definitions, and vortex-core visualization techniques have been proposed during the last 25 years [1– 21]. The recent study of Kolař [21] has pointed out a variety of general requirements for vortex identification, just one of which is the validity of vortex-identification schemes for compressible flows. In this respect, the region-type definitions of a vortex should be distinguished from the line-type definitions of a vortex core [16]. It should be noted, however, that these methods may be generally combined [22]. It is shown subsequently that from the most popular region-type vortex-identification schemes (Q, , 2, and ci), only the criterion and the closely associated ci criterion are directly extendable to compressible flows.