SWIRLING FLOW FORMATIONS IN CIRCULAR CHANNELS

The presented work discusses the topology of swirling flows in circular channels. A comprehensive parameter study is conducted with the objective to investigate the sensitivity of such flows to geometric and fluid mechanic parameters. The swirling flow system in this study consists of a straight tube of large lengthto- diameter ratio with a tangential-type swirl generator at the bottom and a specified outlet at the opposite exit. The study was carried out with the novel measurement technique Phase-Contrast Magnetic Resonance Imaging, which in combination with Laser Doppler Anemometry allowed the time-efficient measuring of more than 70 parameter combinations. The investigated flows are categorized in sub-critical and supercritical states. One major outcome is the finding of a swirling flow that is remarkably robust although it is a sub-critical flow by definition. This flow formation is characterized by a distinctive three-zone axial velocity profile which in this form has not been reported yet in the literature. The corresponding Reynolds number and swirl strength lie within the technical relevant range. Due to its robustness and applicability, the flow is easy to reproduce and therefore ideally suited as a test case for subsequent studies, such as for the validation of numerical codes