Physical properties of vortex and applicability of different vortex identification methods
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Available online at https://link.springer.com/journal/42241 http://www.jhydrodynamics.com Journal of Hydrodynamics, 2020, 32(5): 984-996 https://doi.org/10.1007/s42241-020-0064-7
Physical properties of vortex and applicability of different vortex identification methods * Pei-qing Liu, Yue Zhao, Qiu-lin Qu, Tian-xiang Hu Lu Shijia Laboratory, Beihang University, Beijing 100191, China (Received October 13, 2019, Revised November 22, 2019, Accepted December 23, 2019, Published online October 29, 2020) ©China Ship Scientific Research Center 2020 Abstract: For correct identification of vortices, this paper first analyzes the properties of the rigid vortex core and its induced flow field given by the Rankine vortex model, and it is concluded that the concentrated vortex structure should consist of the vortex core and the induced flow field (the potential flow region with a weak shear layer). Then the vortex structure is analyzed by using the Oseen vortex model. Compared with the Rankine vortex, the Oseen vortex is a concentrated vortex with a deformed vortex core. The vortex structure consists of the vortex core region, the transition region and the shear layer region (or the potential flow region). The transition region reflects the properties of the resultant vorticity of the same magnitude and the resultant deformation rate of the shear layer, and the transition region also determines the boundary of the vortex core. Finally, the evolution of leading-edge vortices of the double-delta wing is numerically simulated. And with different vortex identification methods, the shape and the properties of the leading-edge vortices identified by each method are analyzed and compared. It is found that in the vorticity concentration region, the vortices obtained by using ， 2 ， criteria and Q criteria are basically identical when appropriate threshold values are adopted. However, in the region where the vorticity is dispersed, due to the influence of the flow viscous effect and the adverse pressure gradient, the results obtained by different vortex identification methods can be quite different, as well as the related physical properties, which need to be further studied. Key words: Vortex identification methods, Rankine vortex model, Oseen vortex model, leading-edge vortex, double-delta wing
Introduction The vortex is a common flow phenomenon in nature, closely related to various fluid mechanics fields, including turbulence[1-3], atmospheric phenomena[4-5], ocean physics[6-8], lift augmentation[9-10], drag reduction[11-12], flow control[13-15], and aeroacoustics[16-17]. For example, the trailing-edge vortices and the circulation of the flow around a wing have a dominant impact on the aerodynamic loading of the aircraft. In turbulence studies, it is expected that the mechanism of the turbulence generation and dissipation can be revealed through the study of vortices, and the relationship between the turbulence coherent structure and the flow parameters can be established[1]. The British scientist Küchemann, a student of the
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