Row depth effects on turbulence spectra and acoustic vibrations in tube banks

The effect of row depth on Strouhal numbers derived from peaks in the turbulence spectra measured in an in-line tube bank and on the excitation of acoustic standing waves in the duct containing the bank has been investigated. The results indicate significant variations with bank depth and location in the bank although common features are evident. A buffeting type frequency predicted by Owen 1] is clearly shown beyond the fifth row of deeper banks whilst peaks evident in the turbulence spectra at the front of these banks and for less deep banks are assumed to be generated by vortex action and interaction in the wakes of tube rows. For the geometrical configuration tested, acoustic resonance is generated by the coincidence of a vorticity peak frequency with the standing wave frequency for all cases but the two row deep bank in which the excitation source was most probably in the wake of the bank. Finally, a modification of Owen's theory yields an equation which predicts a Strouhal number of the correct order.