Abstract
The work is aimed at a detailed study of large-scale helical vortex structures emerging in a high turbulent intensively swirling flow. It was shown that the vortex formed in the chamber by installing diaphragm with shifted outlet is folded into a single-helical vortex. The flow visualization shows that although the vortex axis performs slow oscillations (precession), on average this structure is fixed in space. The velocity fields were measured with the aid of a nonintrusive method of flow diagnostics (PIV). Verification of the calculation results obtained using a LES simulation was performed based on measured experimental data to confirm the correctness of the chosen mathematical modelling approach. It has been asserted that the investigated regimes are in a self-similarity area relative to Reynolds number.
Highlights
The application of swirling flows and useful properties of vortex structures has been grounded scientifically and widely used in practice [1]
The frequency of the vortex precession was measured in several ways: based on the analysis of video recordings; using a hydrophone installed on the wall of the channel and based on the numerical simulation using a CFD package by the LES method [6]
As a result of the investigations it was shown that the geometry of the chamber and the boundary conditions have a key influence on the shape of the vortex axis
Summary
The application of swirling flows and useful properties of vortex structures has been grounded scientifically and widely used in practice [1]. There is no quantitative information on such vortices that hinders understanding the physics of formation of vortices and developing approaches for mathematical description of the vortex dynamics. Setting up the experiments with complex swirling flow is a hard task and often it is not feasible to extract enough data, so the numerical modeling plays an important role. The Navier-Stokes equations describing the motion of a viscous fluid are among the most important instruments in hydrodynamics and are used in the mathematical modeling of many natural phenomena and technical processes [3]. Different approaches in the modeling of turbulence make it possible to expand the notion of fluid motion including swirling flows with the formation of complex vortex structures. To verify the simulation results, a joint experimental and numerical study of the vortex structures is used, analogous to [4, 5]
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