Vortex shedding and turbulence scales in staggered tube bundle flows

Time-resolved LDA measurements of the axial and transverse velocity components were performed in the first 6 rows of a staggered tube bundle with relative transverse and longitudinal pitch ratios of 3.6 and 1.6, respectively. Measurements were carried out in a flow of water at a Re-d of 12,858. A flow periodicity with a Strouhal number equal to 0.26 was detected, which is in agreement with published data. This periodicity was found to broaden the turbulence levels by up to 50% in some locations. Agreement between the experimental results and previously reported CFD predictions using the k-epsilon model improved when this periodic component was removed from the spectra using appropriate filtering techniques. In an attempt to describe the turbulence structure more extensively, time-and length-scales and dissipation rates were estimated from the filtered time-resolved data. Integral time scales were on average equal to 4 ms and Taylor microscales 0.7 ms. Comparisons of the data with numerical predictions show promise for more extensive evaluation of CFD predictions in future than has been possible hereto.