ICMF 2016 International Conference on Multiphase Flow Firenze

ICMF 2016 International Conference on Multiphase Flow
Firenze, Italy, May 22 - 27, 2016
DRAG REDUCTION IN TURBULENT PIPE FLOW INDUCED BY SUPERHYDROPHOBIC SURFACE
Roberta Costantini, La Sapienza, Italy; Francesco Battista, Sapienza Università di Roma, Italy; Carlo Massimo Casciola, Sapienza
Università di Roma, Italy
Superhydrophobic surfaces (SHSs), such as those inspired by the self-cleaning property of lotus leaf, are obtained by means of chemical
coating and micro/nano surface texturing. At the macroscopic scales the micro-scale texturing generates a slip velocity at the wall due to
vapor bubbles trapped inside the surface grooves (Cassie-Baxter State). Our aim is to address the effect of SHSs on the drag reduction
in a turbulent pipe flow through the Direct Numerical Simulation (DNS) approach. In particular, the walls of the pipe are decorated with
grooves aligned in the stream-wise direction where the Cassie-Baxter state is artificially enforced via a perfect slip boundary condition on
the macroscopic fluid velocity. The work addresses the effects of the dimension of the grooves on the turbulent structures characteristic
of wall-bounded flows. The main issue of this peculiar configuration consist in the fact that the turbulent pressure fluctuations are likely to
trigger the transition from the Cassie-Baxter to the Wenzel state of the liquid/vapor interface. For this reason, a model mimicking the
dynamics of the liquid/vapor interface is introduced in the DNS to account for the effects of the transition events on the turbulent flow.
The research leading to these results has received funding from the European Research Council under the European Union’s Seventh
Framework Programme (FP7/2007-2013)/ERC Grant agreement n. [339446].