The dynamic evolution of fluid strouhal number under flow fields around flexible vertical pipe groups

Abstract

In this paper, a Strouhal-Reynolds number evolution region for the pipe groups within the subcritical Reynolds number range is established and a Strouhal-Reynolds number relation curve in root mean square terms is yielded for the first time. A Strouhal-Reynolds number model for flow around flexible pipes under 180 sets of test is presented. The least squares method is used to fit the Strouhal numbers among the pipes within their flow velocity intervals; isolated pipe is introduced as reference cases for examining how the Strouhal numbers of the pipes vary with Reynolds number. The results indicate that, when in tandem arrangement, the Strouhal number of the three-pipe group showed a gradual reduction from upstream to downstream whereas both vortex shedding enhancement and suppression occurred in the five-pipe group; interferences contributed to the vortex shedding in the wake flow of the pipes in side-by-side arrangement. It is also found that interferences significantly changed the vortex shedding frequencies on both rear sides of the pipes; only 16.9% of the Strouhal numbers of the three-pipe and five-pipe group fell within [0.185,0.20], which is largely different from conventional cognition of the Strouhal number within the subcritical Reynolds number range.