Development of pre-set counter-rotating streamwise vortices in wavy channel

Abstract

Development of counter-rotating streamwise vortices in a rectangular channel with onesided wavy surface has been experimentally quantified using hot-wire anemometry. The wavy surface has fixed amplitude of 3.75 mm. The counter-rotating vortices are pre-set by means of a sawtooth pattern cut at the leading edge of the wavy surface. Variations of the central streamwise velocity U c with a channel gap H = 35 mm and 50 mm (corresponding to a Reynolds number from 1600 to 4400) change the instability of the flow which can be distinguished from the velocity contours at a certain spanwise plane. The streamwise velocity contours and turbulence intensity for Reynolds number Re = 3100 and H = 35 mm show the disappearance of the mushroom-like vortices prior to turbulence near the second peak of the wavy surface, while for higher Re, this phenomenon occurs earlier. Under certain conditions, for example, for Re = 4400 and H = 50 mm, the splitting of the vortices can also be observed.

Effects of Wavy Channel Entrance Design on Streamwise Counter-rotating Vortices: a Visualization Study

“…When amplitude of the wavy surface is doubled from the amplitude used in the earlier study by Budiman et al (2015), it is found that the streamwise counter-rotating vortices have a notably different appearance, regardless of the Reynolds number. Budiman et al (2015) presented streamwise counter-rotating vortices with a relatively long mushroom stem and small mushroom hat. In contrast, due to larger amplitude used in this study, the mushroom hat was much bigger, as depicted in Figs.…”

“…Smoke-wire flow visualization technique was used in this study, similar to the previous study by Budiman et al (2015). Paraffin oil is selected as smoke-generating fluid.…”

“…3(b). This method has been proven to successfully generate streamwise counter-rotating vortices with nearly uniform spanwise wavelength, which would be useful to avoid subjectivity and difficulty in studying the downstream evolution of the structures (Wortmann 1969;Winoto et al 2005;Budiman et al 2015). …”

Characterization of counter-rotating streamwise vortices in flat rectangular channel with one-sided wavy wall

“…This current study aims to characterize the induced counter-rotating streamwise vortices which evolve in channel flow with one-sided corrugated wall. Recently, Budiman et al (2016) discussed the development of such vortices by means of hot-wire anemometry. However the report is only limited to the spanwise y − z plane.…”

“…However the report is only limited to the spanwise y − z plane. This paper is intended to complement that report by focusing on the streamwise x−y and x−z planes, together with discussions on mixing properties that have not been covered by Budiman et al (2016).…”