Development of laser-optical measurement techniques on the vortex tube: Taking PIV to its limits

Abstract

The Ranque-Hilsch vortex tube (RHVT) is referred to as one of the unsolved problems in physics: consisting of a cylindrical tube with several tangential inlet nozzles only, the expanded gas forms a complex internal flow field, resulting in a unique temperature separation effect. Since the vortex tube’s invention by Ranque (1933) and Hilsch (1947) it has been used for decentralized cooling and gas cleaning purposes. While so far it has been investigated by means of conventional probes as well as laser-optical techniques such as FRS, L2F and LDA, this contribution targets on planar two-component PIV measurements. While the usual configuration features one outlet on each end of the tube, it will be shown that the major internal flow phenomena occur in a similar manner on a uni-flow configuration with only one outlet opposite to the inlet. The focus however is not on the temperature separation. Instead the RHVT is introduced as a development platform for laser-optical methods: it will be shown that the RHVT’s complex flow topology is pushing the PIV technique to its limits; challenges and possible solutions are discussed. Especially the high tangential velocity component results in a strong projection error in the observed axial and radial velocities: to address this issue stereoscopic PIV will be deployed for the purpose of mapping the RHVT.