Experimental investigation of Dean-vortices oscillation downstream of a 90° Bend

The present work experimentally investigates the dynamics of a pipe flow downstream of a 90° bend in turbulent regime. The study is carried out on two different test benches, enabling to cover a decade in Reynolds numbers ($Re\in [1.2\times 10^4,5.4\times 10^5]$). Laser-based metrology techniques are employed to capture the three velocity components in several flow sections, namely, cross-sections orthogonal to the main flow and vertical diametral planes (parallel to the main flow direction). Time-resolved and long-time decorrelated measurements allow the characterisation of both the dynamics and the statistics of the flow. These measurements highlight the behaviour of the fully three-dimensional flow generated downstream of the bend. In particular, an oscillation of the dipolar structure generated by the bend, known as the Dean vortices, is measured and analysed using a Lamb–Chaplygin analytical model. The dependency of the flow behaviour as a function of both the Reynolds number and the distance downstream of the bend and the return to axisymmetric flow are evaluated.