### LANS Publications

# "Direct Simulation of Turbulent Swept Flow Over a Wire in a Channel"

R. Ranjan, C. Pantano, and P. Fischer

*Journal of Fluid Mechanics*, vol. 651, , pp. 165-209. Also Preprint ANL/MCS-P1733-0310

Preprint Version: [pdf]

The turbulent swept flow around a cylindrical wire resting on a wall of a channel is investigated using direct numerical simulation. This geometry is a model of the flow through the wire-wrapped fuel pins, the heat exchanger, typical of many reactor designs. Mean flow along and across the wire axis is imposed, leading to the formation of separated and reattached secondary flow regions. The Reynolds number based on the centerline velocity along the wire axis direction is 6000 and four cases are simulated with different flow rates across the wire. This configuration is topologically similar to backward-facing steps or slots with swept flow, except that the dominant flow is along the obstacle axis in the present study and the cross flow is smaller than the axial flow, i.e. large swept. Mean velocities, turbulence statistics, wall shear stress probability distribution functions and instantaneous flow structures are investigated. Particular attention is devoted to the statistics of the shear stress on the walls of the channel and wire in the recirculation zone. The effect of cross-flow strength on the statistics is discussed. The flow around the mean reattachment region, at the termination of the recirculating bubble, does not exhibit the typical decay of the mean shear stress observed in classical backward facing step flow as one approaches this region owing to the presence of a strong axial flow. There is, nevertheless, a change in the mean angle of the wall shear stress from the external to the recirculation region. Normalized probability density functions of wall shear stress exhibit a weak dependence across the wall of the channel. This is consistent with the presence of strong axial flow, which keeps the flow highly turbulent irrespective of the strength of the cross-flow, except within the secondary flow regions that appear to laminarize.