Abloesungs- und Widerstandsphaenomene in periodisch-verengten Rohren bei niederen Reynolds-Zahlen

Abstract

Flow separation and resistance phenomena in sinusoidally constricted tubes of different geometrical shapes were studied experimentally and numerically at low Reynolds numbers (10"-"4#<=#Re#<=#10"2). Flow separation is demonstrated to occur even for creeping flow (Re<<1), with the geometrical parameters chosen adequately. Surprisingly, when the amplitude-to-wavelength ratio #gamma# is kept constant and only the ratio of the mean radius to the wavelength (titled #delta#) is varied, separation under creeping flow conditions is found to take place solely for small values of #delta#, whereas flows under the influence of inertia (Re>1) tend to separate for small values of #delta# as predicted by the classical concept of flow separation. This behaviour demands explanation. As far as kinematics is concerned, the separation zones have a very symmetrical appearance for creeping flow; become rather unsymmetrical with the beginning influence of inertia and regain a more symmetrical shape only for higher Re before the transition to turbulence takes place. For one specific #gamma# it could be shown numerically that as #delta# was increased the Re-Number for beginning separation first increases, but then decreases after having reached a maximum to yield a creeping flow separation. (orig.)49 refs.Available from TIB Hannover: RA 1396(1995,5) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman