Large Eddy Simulations of Static and Rotating Ribbed Channels in Adiabatic and Isothermal Conditions

In an attempt to better understand spatially developing rotating cooling flows, the present study focuses on a computational investigation of a straight, rotating rib roughened cooling channel initially numerically studied by Fransen et al. [1]. The configuration consists of a squared channel equipped with 8 rib turbulators placed with an angle of 90 degrees with respect to the flow direction. The rib pitch-to-height (p/h) ratio is 10 and the height-to-hydraulic diameter (h/Dh) ratio is 0.1. The simulations are based on a case where time resolved two-dimensional Particle Image Velocimetry (PIV) measurements have been performed at the Von Karman Institute (VKI) in a near gas turbine operating condition: the Reynolds number (Re) and the rotation number (Ro) are around 15000 and ± 0.38 respectively. Adiabatic as well as anisothermal conditions have been investigated to evaluate the impact of the wall temperature on the flow, especially in the rotating configurations. Static as well as both positive and negative rotating channels are compared with experimental data. In each case, either an adiabatic or an isothermal wall boundary condition can be computed. In this work, Large Eddy Simulation (LES) results show that the high fidelity CFD model manages very well the turbulence increase (decrease) around the rib in destabilizing (stabilizing) rotation of the ribbed channels. Thanks to the full spatial and temporal description produced by LES, the spatial development of secondary flows are found to be at the origine of observed differences with experimental measurements. Finally, the model is also able to reproduce the differences induced by buoyancy on the flow topology in the near rib region and resulting from an anisothermal flow in rotation.Copyright © 2017 by ASME