Numerische Untersuchung der turbulenten Strömung durch parallele Kanäle, die durch einen Spalt miteinander verbunden sind

Large-scale quasi-periodic flow motions between subchannels are observed for axial turbulent flow through rod bundles. The origin and source of the pulsations are not yet completely understood. A more general geoinetry consisting of two parallel rectangular channels connected by a gap has been experiinentally investigated using hot wire anemometry. The results of these ineasurements are presented. The characteristic phenomena of flows through gaps known froin similar geoinetries were also found for the cross-section investigated here. This concerns unusually high values for turbulence intensities, Reynolds shear stresses and spectral power densities in certain regions of the gap. An appropriate geoinetry has been nuiiierically investigated. For that purpose the large eddy siiiiulation inethod (LES) has been used. After the presentation of the theoretical basis of the LES methodical modifications and adaptions of the code TURBIT necessary for the treatiiient of the Special probleiii are explained. The influence of paraineters like Reynolds nuiiiber, mesh size and periodicity length on the results of the siiiiulation is also described. After a variation of these paraiiieters the siinulation results qualitatively differ only negligibly. Decreasing the Reynolds number and refineiiient of the grid lead to a siiioothing of the contour-lines. A variation of the periodicity length affects the number of pairs of vortices in the channel. The results of the iiieasureinents and of the siiliulation are coiilpared for one siiliulation case. A good qualitative agreeinent is observed, especially in the gap region. The siinulation reproduces all characteristic effects known froin the ineasurement. The flow inodel for the gap region which was proposed after the evaluation of the ineasureiiient is confiriiied by the siiiiulation. The fundaiiiental phenoiiienon responsible for the characteristic effects in the gap region is a sequence of pairs of vortices which are transported through the gap in the iiiain flow direction. The driving mechanism of these vortices results from the difference between the flow velocities in the channel and in the gap. The appearance of the characteristic phenoinenon in the calculation, where a developed flow is simulated, shows that this effect is not caused by the inlet conditions but is a characteristic of the particular geometry.