Measurements of the mean velocity, wall shear stresses, and turbulent Reynolds stresses were performed in wall subchannels of two rod bundles. The rod bundle of four parallel rods was arranged symmetrically in a rectangular channel. The pitch-to-diameter ratio was 1.148, and the wall-to-diameter ratios were 1.045 and 1.074, respectively. The Reynolds numbers in these investigations were 6.11 × 104 and 7.07 × 104, respectively. The experimental results demonstrate once more that the structure of turbulence in rod bundles differs greatly from the structure in circular tubes. Especially in the narrow gaps between the rods and channel walls, there are increased levels of turbulence intensities in both the axial and azimuthal directions and, hence, of the kinetic energy of turbulence, caused by a strong turbulent momentum transport through the gaps. In comparison with the previous investigations in these geometries, however, arranged asymmetrically in the rectangular channels, the momentum transport between the subchannels across the gap between the rods is negligible. The comparison between the experimental wall shear stress distributions and those computed by the VELASCO code shows strong deviations, especially in the gap regions between the rods and channel walls. More sophisticated analytical tools than presently available are required to predict turbulent flow through rod bundles with sufficient accuracy.
