Numerical modeling of vortex shedding in helically wound finned tube bundles in cross flow

Periodic vortex shedding can be a challenge for fin-tube heat exchanger reliability if the shedding frequency coincides with the natural frequency of the heat exchanger tubes. Current design methodologies are primarily developed for bare tube arrays and it is not clear whether they are directly transferable to fin-tube bundles. This work addresses the issue by performing transient Computational Fluid Dynamics simulations of the flow through a small periodic section of three tube bundles, having high fins, low fins and bare tubes, respectively. Strouhal numbers and dynamic lift coefficients are compared with literature data and -equations. Results indicate that the vortex shedding frequency follows the expected trend with respect to the tube pitch ratio, if an effective diameter is used to normalize the fin-tube data. Similarly, the lift coefficients for identical tube bundles with and without fins are approximately equal when the effective diameter is used to normalize the fin-tube bundle data. These findings have implications for the design of weight/volume optimized heat exchangers, but experimental validation is required.