Heated cylinders can be frequently observed in industrial applications. Heat exchanger tubes, pin fins in electronic components, and nuclear reactor control rods are some of the examples which can be modeled as heated cylinders exposed to fluid flow. Any bluff body subjected to fluid flow experiences flow induced vibrations due to the induced aerodynamic forces which can have catastrophic results. The two types of flow induced vibrations encountered in practice are streamwise (parallel to the flow direction) and spanwise (normal to the flow direction). The influence of spanwise vibrations coupled with various levels of heating, on the lift and drag forces, is numerically studied in this work. The flow domain consists of a circular region of 64D surrounding the circular cylinder of diameter D. To obtain a good compromise between solution accuracy and computational time, the movement of cylinder is confined in a region of 2D and the dynamic mesh technique is applied in this domain, whereas the cells outside this domain remain fixed. Transient analysis is conducted to solve URANS using Ansys/Fluent for laminar flow of Re 100 . Spanwise forced oscillations are carried out using user-defined-functions to mimic the flow induced vibrations. Amplitude of oscillation is kept fixed at 0.1D and frequency of oscillation is varied according to the frequency ratios (f/fn) of 0, 0.5, 1, 1.5, and 2, where 0 means the cylinder is stationary, at four different levels of heating, ΔT = 0 for isothermal, and ΔT = 300, 600, 900 for non-isothermal flow, where ΔT is the temperature difference between the cylinder wall and the oncoming fluid. Air is taken as the fluid and temperature dependent properties of air are considered as the properties change significantly in the given temperature range. Mesh sensitivity is done initially to gain good fidelity of the discretized flow domain and the model is validated using the experimental results from the literature. The non-dimensional natural vortex shedding frequency of the stationary cylinder for isothermal flow is found to be 0.165 marking its Strouhal number, and it is observed that rms of the lift coefficient and average drag coefficient both increase with an increase in the frequency ratio, but a large increase in the drag coefficient is observed at the frequency ratio of 1 marking the lock-on phenomena. Fast Fourier Transform (FFT) of the lift coefficient revealed only one frequency for frequency ratio of 0 and 1 at the natural frequency of the cylinder whereas for other values of frequency ratio, two peaks are observed, one for the natural frequency and the other for the forcing frequency. For all values of frequency ratio, an increase in the temperature difference (ΔT) results in decrease in the lift and increase in the drag coefficient. Heating the cylinder also decreases the natural frequency of vortex shedding. Increasing ΔT to 300 and 600 decreased the natural vortex shedding frequency by 14.29% and 28.03%, respectively. It is observed that vortex shedding stops at ΔT of 900 for stationary cylinder and for forced oscillating cylinder only one peak is seen&nbsp; in FFT corresponding to the forcing frequency. Increasing ΔT to 300, 600, and 900, increases drag by 7.33%, 11.65%, and 16.52%, respectively, for stationary cylinder and a similar trend in observed for the oscillating cylinder. These results show that heating the cylinder decreases the lift coefficient and the natural vortex shedding frequency of the cylinder, whereas it increases the drag coefficient. &nbsp;Keywords: flow induced vibrations, oscillating cylinder, spanwise oscillations, heated cylinder, lift and drag.

Heated Circular Cylinder Subjected to Forced Spanwise Oscillations

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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