When a fluid flows in a cross flow over a tube, vortices are shed from the downstream side. The frequency/of vortex shedding is characterized by the Strouhal number, Sr = fd /u, where d is the tube diameter and u is the fluid velocity, lit tube banks [where u is normally defined from Equation 16076.4 and Equation 16076.5], the pattern of vortex shedding is complex and gives rise, in some geometries, to much higher values of Sr than for single tubes. An analysis of the results for Sr for a wide range of Re, a, and b for in-line and staggered banks suggests that there is usually no significant effect of Re on Sr. However, results obtained by the present authors for staggered banks with the relative longitudinal pitch b = 2.5 indicate that Sr decreases by 50% with increasing Re.

Figure 1 and Figure 2 present values of Sr obtained by the present authors and others (Fitz-Hugh, 1973 and Chen, 1972) for symmetric in-line (a – b) and staggered (s₁ = s₂) banks with a in the range 1.25–3.5. They suggest that Sr decreases with increasing a (or b) and approaches a constant value at high values of a. The following relationships fit the curves shown in Figure 1 and Figure 2.

Figure 1 Strouhal number as a function of a for symmetric staggered banter Curve 1, first row. Curve 2, inner row

Figure 2 Strouhal number as a function of a for symmetric in-line banks

For the first row of symmetric (s₁ = s₂) staggered banks, for 1.25 < a < 2.0 and Re < 1.5 × 10³,