A study on axially rotating pipe and swirling jet flows
Sammanfattning: The present study is an experimental and numerical investigation on rotating flows.A special facility has been built in order to produce a turbulent swirling jet generated by a fully developed rotating pipe flow and a Direct Numerical Simulation (DNS) code has been used to support and to complement the experimental data. The work is so naturally divided into two main parts: the turbulent rotating pipe flow and the swirling jet.The turbulent pipe flow has been investigated at the outlet of the pipe both by hot-wire anemometry and Laser Doppler Velocimetry (LDV). The LDV has also been used to measure the axial velocity component inside the pipe. The research presents the effects of the rotation and Reynolds number (12000 Re 33500) on a turbulent flow and compares the experimental results with theory and simulations. In particular a comparison with the recent theoretical scalings by Oberlack (1999) is made.The rotating pipe flow also represents the initial condition of the jet. The rotation applied to the jet drastically changes the characteristics of the flow field. The present experiment, investigated with the use of hot-wire, LDV and stereoscopic Particle Image Velocimerty (PIV) and supported by DNS calculation, has been performed mainly for weak swirl numbers (0 S 0.5). All the velocity components and their moments are presented together with spectra along the centreline and entrainment data.Time resolved stereoscopic PIV measurement showed that the flow structures within the jet differed substantially between the swirling and no swirling cases.The research had led to the discovery of a new phenomenon, the formation of a counter rotating core in the near field of a swirling jet. Its presence has been confirmed by all the investigation techniques applied in the work.
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