Unstable vortex flow and new inertia-driven vortex rolls resulting from an air jet impinging onto a confined heated horizontal disk

Laminar flow in radial flow cell with small aspect ratios: Numerical and experimental study

“…This assumption is generally made for studies dealing with confined impinging jets or with the RFC (Chatterjee, 2000;DiMilla, 1997, 1998;Moller, 1963;Park et al, 2003). However, asymmetries resulting from inertial effects have been reported for aspect ratios e > 2 (Hsieh et al, 2006;Hsieh and Lin, 2005;Nakabayashi et al, 2002) and were observed here as well. These asymmetries appear above a certain value of Reynolds number and consist of slight oscillations of the detachment and reattachment position of the recirculation zones.…”

“…They showed that, for an aspect ratio of e = 2, if Re Di continues to increase, three recirculation zones can be detected; the primary, the secondary and a tertiary one within the primary. An even more complex flow pattern was reported by Hsieh et al (2006) with the presence of a quaternary recirculation zone for Re Di = 1150, at the same aspect ratio. However, if the disc spacing is reduced, the size of these recirculation zones diminishes and their onset Reynolds numbers increase, explaining why only one recirculation zone was observed by DiMilla (1997, 1998) at Re Di = 1500 for e = 0.2.…”

“…These asymmetries appear above a certain value of Reynolds number and consist of slight oscillations of the detachment and reattachment position of the recirculation zones. They can lead up to a rotating motion of the flow pattern around the inlet axis but tend, however, to disappear when the aspect ratio is reduced (Hsieh et al, 2006).…”

“…These instabilities appear at values of Re Di which increase when the aspect ratio decreases: Re Di = 1041 for e = 2 and Re Di = 798 for e = 4 (Hsieh et al, 2006;Hsieh and Lin, 2005). The amplitude of the flow oscillations in the recirculation zones was reported to be small for e = 2 and 4, in comparison with an aspect ratio of 6 for instance (Hsieh et al, 2006).…”

“…Reported instabilities for e 2 are the oscillation of the radial position for the detachment and reattachment of the flow in the recirculation zones (Hsieh et al, 2003(Hsieh et al, , 2006Nakabayashi et al, 2002), the rotation of the flow pattern around the inlet axis (Hsieh et al, 2003(Hsieh et al, , 2006 and the apparition of radial streaks, which translate circumferential instabilities in the flow (Nakabayashi et al, 2002). These instabilities appear at values of Re Di which increase when the aspect ratio decreases: Re Di = 1041 for e = 2 and Re Di = 798 for e = 4 (Hsieh et al, 2006;Hsieh and Lin, 2005). The amplitude of the flow oscillations in the recirculation zones was reported to be small for e = 2 and 4, in comparison with an aspect ratio of 6 for instance (Hsieh et al, 2006).…”