Transitional and Turbulent Bent Pipes
We review a number of aspects of the transitional and turbulent flow in bent pipes, obtained at KTH using the spectral-element code Nek5000. This flow, sometimes also called Dean flow, is characterised by the appearance of Dean vortices, which arise due to the action of the centrifugal force in the bend. We start with reviewing recent stability analysis in the toroidal flow, and conclude that for all curvatures \(\delta >0\) an exponential instability is present at a bulk Reynolds number of about 4000. Further increasing the Reynolds number lets the flow go through a region with potential sub straight and sublaminar drag. An analysis using proper orthogonal decomposition (POD) reveals that wave-like motions are still present in the otherwise turbulent flow. Upon further increasing Re, the in-plane Dean vortices lead to a modulation of turbulence depending on the azimuthal position. The flow is then dominated by low-frequency so-called swirl-switching motion. This motion is studied in both a periodic and spatially developing framework. Finally, the effect of Dean vortices on Lagrangian inertial particles is studied.
Financial support by the Swedish Research Council (VR) and the Knut and Alice Wallenberg Foundation (KAW) is gratefully acknowledged. Most of the simulations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC) and PDC (Stockholm). Additional simulations were performed within the DECI-project PIPETURB.
- 2.L. Hufnagel, On the swirl switching in developing bent pipe flow with direct numerical simulation, Master’s Thesis, KTH Mechanics, 2016Google Scholar
- 5.P.F. Fischer, J.W. Lottes, S.G. Kerkemeier, Nek5000 Web page, 2008, http://nek5000.mcs.anl.gov
- 7.J. Canton, Global linear stability of axisymmetric coaxial jets, Master’s Thesis, Politecnico di Milano, 2013Google Scholar
- 8.J. Canton, R. Örlü, P. Schlatter, Characterisation of the steady, laminar incompressible flow in toroidal pipes covering the entire curvature range, submitted (2017)Google Scholar
- 13.C. Brücker, A time-recording DPIV-study of the swirl switching effect in a 90\(^\circ \) bend flow. 8th International Symposium on Flow Visualization, Sorrento, Italy p. 171 (1998)Google Scholar