Flow structures in a swirl flow - vortex breakdown condition

C Biegger,B Weigand,F Marsik,M Tomas,P Novotny

doi:10.1088/1742-6596/1045/1/012031

C Biegger, B Weigand + Show 3 more

Open Access

https://doi.org/10.1088/1742-6596/1045/1/012031

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Abstract

This paper presents an experimental and numerical analysis of swirl flow in a circular tube. Swirl flow is important for technical and natural processes, where high heat transfer and good fluid mixing are needed. Flow and vortex structures respecting redistribution of momentum and possible occurrence of vortex breakdown are taken into account. The swirl flow is analysed experimentally by the measurement of the velocity field using Particle Image Velocimetry (PIV) and numerically via the commercial CFD code ANSYS CFX. Three cases are investigated: laminar flow regime (Re = 1,000), intermediate flow regime (Re = 2,000), and turbulent flow regime (Re = 5,000). The redistribution of the velocity field and the decrease of the swirl strength towards the outlet are shown. This redistribution affects the Reynolds number. Concerning the Rossby number, the occurrence of vortex breakdown in the swirl flow is determined. It is shown that the vortex breakdown takes place in the flow with higher Reynolds numbers, where an axial backflow may occur. Changes of the Reynolds numbers Reϕ and Rez along the tube length also confirm this statement. Furthermore, a thermodynamic perspective of vortex breakdown phenomena is presented.

Highlights

Swirl flow has an impact in several technical applications due to its influence on fluid mixing and heat transfer
Vortex breakdown can be predicted by a change of the two different Reynolds numbers, the axial Reynolds number (Rez) and the tangential Reynolds number (Reφ), equation (6), respectively
In contrast to the analysis based on the Rossby number, these Reynolds numbers are used to study the effect of the mean velocities

Summary

Introduction

Swirl flow has an impact in several technical applications due to its influence on fluid mixing and heat transfer. Glezer et al [11] focused on the internal swirling flow and its influence on the heat transfer They used a test rig simulating a rotating leading edge internal passage of a blade with heated walls and a screw - shaped cooling swirl resulted from flow generated by tangential slots. They stated that Coriolis forces appearing during blades rotation had a positive influence on the internal heat transfer in case of the same direction of the Coriolis forces with the tangential velocity component.

Procedures

Flow analysis

Results