Direct numerical simulation of a turbulent curved pipe flow with a 90° bend

Abstract

Direct numerical simulations (DNS) have been performed for a turbulent curved pipe flow going through a 90◦ bend at Reynolds number ReD = 5300 (or Reτ = 180). The swirl switching phenomenon downstream of the bend is investigated. Mean turbulence statistics in both upstream and downstream of the bend are compared with available DNS and experimental data, and very good agreements have been achieved. Two significant force oscillations in the downstream of the bend are observed: spatial oscillation along the flow direction and temporal oscillation at pipe cross-sections. It is found that the quasi-periodic force oscillation is closely associated with the unsteady motions of Dean vortices. Conditional-averaged flow fields based on positive and negative forces show mirror states of the Dean vortices with one of them being suppressed. It is also observed that the mean flow oscillation is strongly linked with the swirl switching phenomenon.