An LDA of the precessing vortex core in a cyclone

In a cyclone the centre of the swirling flow, denoted as the vortex core, is precessing about the geometrical centre of the cyclone. In this research project, the aim was to get more insight in the influence of this precessing vortex core (PVC) on the velocity field of the cyclone. Therefore, at several horizontal stations Laser Doppler Anemometry (LDA) measurements were carried out to determine the axial and tangential velocity components along the cyclone radius. A trigger procedure has been developed to estimate the velocity profiles corresponding to the extreme positions of the PVC with respect to the LDA-probe. This trigger procedure makes use of the periodical component in the measured tangential LDA signal itself to estimate the trigger time intervals. To estimate the periodical interference from the tangential velocity signal, an adaptive noise canceling configuration (ANCC) has been implemented. This algorithm is capable of tracking the quasi periodic circular movement of the PVC. By combining the trigger procedure and the ANCC it is possible to estimate the triggered profiles of both the axial and the tangential velocity components. The resulting standard deviation of the triggered velocity does not show the expected decrease. By subtracting the estimation of the periodical component and the tangential velocity signal, the standard deviation in the centre of the cyclone was reduced by 40%. A remarkable observation was the disappearance of the periodical interference in the LDA signal at r ? 0.6Rc for all measured profiles. It was assumed that the extreme velocity profiles intersect at this position. Further research is necessary to confirm this.Kramers Laboratorium voor Fysische TechnologieApplied Science