Characterization of the flow field inside a Ranque-Hilsch vortex tube using filtered Rayleigh scattering, Laser-2-Focus velocimetry and numerical methods

Abstract

The design process of aero engines as well as stationary gas turbines is largely dominated by the cost and time efficient methods of Computational Fluid Dynamics (CFD). Over the past decade the CFD solver TRACE for Favre-averaged compressible Navier-Stokes equations has been developed at the Institute of Propulsion Technology and has been adopted for research as well as industrial applications. In the context of turbomachinery design, reliable modeling of the turbulent flow phenomena involved is a crucial aspect and one of the major subjects of numerical research in fluid dynamics. Novel approaches accounting for the anisotropy of the Reynolds stress tensor promise an improved accuracy in the simulation of industrially relevant configurations. One key aspect in the development strategy of turbulence models is the direct comparison of computational results with validation data produced from appropriate experimental setups with well-defined geometries and boundary conditions. The Ranque-Hilsch vortex tube (RHVT) was chosen in this respect due to its simple geometry with no moving parts on the one hand and its nevertheless complex 3D flow features on the other hand. To provide suitable experimental data the filtered Rayleigh scattering technique extended by the method of frequency scanning (FSM-FRS) was chosen to characterize the RHVT's averaged flow field, since it is capable of simultaneously providing planar information on temperature, pressure and flow field velocity (through the Doppler shift). As the reconstruction of a three component velocity field from FSM-FRS data would require the measurement plane to be observed from three independent directions, the point-wise Laser-2-Focus (L2F) technique is applied to provide 2C velocity profiles at discrete positions downstream from the cold exit.