<p>Heated cylinders are commonly found in industrial applications. Generally, a single heat exchanger tube can be modeled as heated cylinder subjected to free stream fluid flow. Pin fins in electronic components, nuclear reactor control rods and heat exchanger tubes can all be viewed in a simplified way as a system with fluid flow over a heated cylinder, i.e. non-isothermal flow. Cylinder subjected to flow experiences flow induced vibrations due to aerodynamic forces which can compromise system integrity and lead to structural damages. Flow induced vibration is normal to the direction of incoming flow, however this study focuses on the vibrations in streamwise direction. The influence of vibration and heat transfer on the lift force is numerically studied in this work. Temperature difference of 300K is used between the cylinder wall and the incoming fluid flow for Reynolds number of 100. Air is used as the fluid and the temperature dependent properties of air are used for the analysis as a significant change in the properties of air incurred, i.e. 4.1%-142.1% at the selected operating temperature range of 300–600K. Numerical simulation is done using Ansys/Fluent with O-type mesh and the vibration in the cylinder is induced using user defined function. Mesh sensitivity was done initially to gain good fidelity of the discretized flow domain and obtained solution.&nbsp; The vibration of cylinder in streamwise direction is induced at frequency range of 0.5–2.5 Hz, with the natural frequency of the cylinder being 2.5 Hz marking its Strouhal number. It is observed that for all the induced frequencies, the forcing function interacts with the natural frequency of the system and beating phenomenon spectrum is observed, where two distinct frequencies appear which correspond to the sum and difference between the natural and the forcing frequency. At the inducing frequency of 1 Hz, the of lift coefficient is characterized with three frequencies: 2.5 Hz (natural frequency), 3.5 Hz (sum) and 1.5 Hz (difference). As compared to stationary isothermal cylinder, heating the cylinder decreases the rms value of the lift amplitude by 64.8% and its frequency by 14.6%. Oscillating the isothermal cylinder at 1 Hz causes a negligible increase in the rms value of the lift amplitude by 1.36% and has no effect on the value of natural frequency of the system. Heating the oscillating cylinder decreases the rms value of the lift amplitude by 47% and its natural frequency by 7.64%. A similar trend is seen in the other inducing frequencies. These results show that heating the cylinder decreases the lift coefficient amplitude and the natural frequency of the system which is beneficial for the industrial applications such as heat exchanger tube bundles.</p>

Dynamic Behavior of  a Streamwise Oscillating Heated Cylinder

Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2021/volume/84874

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