Vortex shedding characteristics and aerodynamic forces of a finned cylinder in cross-flow

The vortex shedding characteristics and aerodynamic forces of a crimped, spirally finned cylinder in cross-flow are experimentally investigated within Reynolds number range of 20×103≤ ReDeq ≤60×103, where Deq is the equivalent diameter. Three different finned cylinders with varying fin pitch-to-root diameter ratios (p/Dr) are studied and compared to their equivalent diameter (Deq) bare cylinder. In comparison to the bare cylinder, the finned cylinders exhibit a notably enlarged vortex formation length. This is due to a lower Coriolis acceleration as a result of a lower vortex force within the formation region. Reduction in the p/Dr led to a progressive increase in the vortex force. This led to a gradual decrease in the vortex formation length. Moreover, the increase in the vortex force resulted in a notable increase in the transverse Reynolds stresses and the development of more concentrated vortex cores. Indicative of a more correlated vortex shedding process, at certain p/Dr, the contribution of the coherent portion of the transverse Reynolds stresses to the total transverse Reynolds stresses exceeded that of the bare cylinder. However, due to the weaker vortex force, the amplitude of the periodic portion of the transverse Reynolds stresses never exceeded that of the bare cylinder. Although for certain p/Dr, the vortex shedding process was more correlated, the combination of an elongated vortex formation length and lower vortex force resulted in weaker dynamic loading on the finned cylinders in comparison to the bare cylinder case. The findings of this study show that the equivalent diameter approach is flawed, as it does not capture any of the intrinsic changes in the flow characteristics and hence the dynamic loading on the finned cylinders.