Unsteady Secondary Motion of Pulsatile Turbulent Flow through a Double 90°-Bend Duct

Oki Junichi

Kuga Yukika

Yamamoto Ryo

Nakamura Kazuhiro

Yokohata Hideaki

Nishida Keiya

Ogata Yoichi

Flow, Turbulence and Combustion

We investigate turbulent flow with highly pulsating axial velocity passing through a duct with both first and second bends. The time-dependent velocity fields downstream of the bends were measured using time-resolved stereo particle image velocimetry for the steady case (Reynolds number Re = 36,700) and the pulsatile case (Re = 37,800 and Womersley number α = 59.1). Proper orthogonal decomposition (POD) of the in-plane velocity data isolates the energetic structures of the secondary flow. The modes downstream of the first bend have a Dean motion (mode 0), single swirl (mode 1), and double swirl (mode 2), which agree with those of previous studies on steady turbulent flow. Downstream of the second bend, additional vortices appear in the modes owing to the secondary flow originating in the first bend. The modal structure of the pulsatile case is virtually the same as that of the steady case. To our knowledge, we are the first to find swirl switching in pulsatile flow, whereas the switching has been reported only for steady cases. We further conduct a time-frequency analysis via wavelet transformation onto the POD time coefficient, showing intermittency in energy of the mode associated with swirl switching.

Turbulence

Pulsatile flow

Secondary flow

Particle image velocimetry

Swirl switching

eng

Springer

This is a post-peer-review, pre-copyedit version of an article published in Flow, Turbulence and Combustion. The final authenticated version is available online at: https://doi.org/10.1007/s10494-019-00088-y.

This is not the published version. Please cite only the published version. この論文は出版社版ではありません。引用の際には出版社版をご確認、ご利用ください。

[ISSN] 1386-6184

[ISSN] 1573-1987

[DOI] 10.1007/s10494-019-00088-y

[DOI] https://doi.org/10.1007/s10494-019-00088-y