Roughness and rotating fluid turbulence

Turbulent flows in rotating systems are of major practical concern in gas turbines and hydraulic machinery. It is well known that system rotation affects not only the mean fluid motion but also the turbulence field. The Coriolis force arising from the rot ation of the frame-of-reference gives rise to secondary flows which crucially alter the mean flow pattern and thereby the throughflow. Surface roughness is generally known to increase the flow resistance in pipes and channels, but the knowledge about the effect of roughness on the flow in a rotating passage is meager. The project?s overall aim is to explore the effects of surface roughness on the turbulent flow through a rotating channel. It is hypothesized that the pressure loss will be correlated not only with the relative roughness height but also with the rate of rotation. To enable an in-depth exploration of the turbulent flow in a rough-wall rotating channel, direct numerical simulations will be performed. This implies solutions of the time-depen dent Navier-Stokes equations on a three-dimensional grid with typically 100 million nodes on the national high-performance computers. Of particular interest is to investigate if and how the instantaneous flow field in the vicinity of the roughness elemen ts is affected differently depending on the sense of rotation.