Fully Developed Turbulent Flow Through a Rod Cluster.

The work described is an experimental study of developed single phase turbulent axial flow through a closely spaced symmetrical square-pitch rod array spaced at two p/d ratios, 1.194 and 1.107. Air was the working fluid; measurements were made of the mean velocity and wall shear stress distribution by Pitot and Preston tubes, and of the six Reynolds stresses by a two-element rotated hot wire anemometer probe. A PDP 11/10 computer located 150 m away from the experimental rig was used to automate the probe traverse, signal gain and data processing system. Techniques were developed to test the closure of the small signal approximations to the hot wire correlations, and to monitor continuously the drift of the hot wire elements. Three Reynolds numbers, 48.0 x 10('3), 95.8 x 10('3) and 155 x 10('3) were studied for the p/d ratio of 1.194. The mean velocity profiles were scaled by the law of the wall, although the Reynolds stresses, particularly for the open rod gap, showed a marked departure from the distribution associated with axisymmetric pipe flow. Some evidence of secondary flow cells was shown by the hot-wire probe, with further confirmation by azimuthal translation of a innent gas plume injected near to the rod surface. There was no Reynolds number dependence of any parameters. A single study at a Reynolds number of 48.0 x 10('3) was made for the p/d ratio of 1.107. The mean velocity profiles were also scaled by the law of the wall, with the Reynolds stresses showing more extreme differences to pipe flow. No secondary flow cells were shown, however, by either hot-wire anemometry or the gas plume. The Reynolds stress distribution and tracer gas measurements for both p/d ratios support the existance of considerable azimuthal turbulence mixing in the rod gap region.