Flow patterns and energy parameters for a separation flow in a channel with low-height transversal obstacles
N.S. Dushin
Federal Research Center “Kazan Scientific Center of RAS”, Kazan, Russia
Keywords: intermittent roughness, optical measurement, visualization, velocity pulsation, energy, spectrum, turbulence scale, spatial-temporal structure
Abstract
An experimental study was performed for a flow in a channel with an intermittent pattern of roughness. The influence of the relative obstacle height (ranging from 2 to 10 % of the channel height) on the turbulence characteristics and flow structuring in the channel nearwall zone was studied. The research was focused on the case of obstacles with a low height. We found that the obstacle height below 5.5 % induces a drastic change in pulsation and spatial flow characteristics; this alters the flow pattern in the separation zone and the vortex generation mechanisms. The across size of vortex behind the obstacle with a relative height of 2 % is twice as big as the obstacle height. The characteristic peak in spectra that corresponds to the vortex shedding frequency with fully developed roughness tends to degenerate with a decrease in the obstacle height. Here the key factor for vortex generation is due to vertical swing motion of the boundary for separation zone.
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