The influence of temperature gradient on the Strouhal–Reynolds number relationship for water and air

This paper focuses on the wake flow behind a heated circular cylinder in the laminar vortex shedding regime. The phenomenon of vortex shedding from a bluff body is an interesting scientific and engineering problem. Acquisition of reliable experimental data is considered an indispensable step toward a deeper physical understanding of the topic.An experimental study of the wake flow behind a heated cylinder in the forced convection regime is performed using water as the working fluid. Firstly, qualitative visualization experiments were performed and the parallel vortex shedding mode was adjusted. Next, hot-wire anemometry was used for St–Re data acquisition. Data analysis confirmed the so-called thermal effect in water: cylinder heating increases the vortex shedding frequency and destabilizes the wake flow.The effective temperature concept was used and the St–Re data were successfully transformed to the St–Reeff curve. Furthermore, a comparison with air as the working fluid was discussed (cylinder heating decreases the vortex shedding frequency in air, thus stabilizing the wake flow). The formula to determine the effective temperature in water was experimentally derived from the present data, while the data and formula for air is already known. The relationship between the Strouhal number and the effective Reynolds number for water and air is represented by the same, universal formula: St=0.2660-1.0160Reeff-0.5, where Reeff is calculated at the effective temperature.Finally, the measurement results were compared to the thermodynamic St–Re equation derived by Maršík et al. [F. Maršík, Z. Trávníček, R.H. Yen., A.-B. Wang, Fluid dynamics concept for the critical Reynolds number of a heated/cooled cylinder in laminar crossflow, in preparation]. A satisfactory agreement between the derived equation and experimental data for both fluids (water and air) was achieved.