Study On The Flow-induced Vibration And Heat Transfer Characteristics Of Two 2-D Cylinders

Vibrating in heat transfer enhancement was paid attention in 70's last century. With the development and progress of technologies, the subject was mentioned more and more. The research in heat transfer mechanism of vibrating surface would be a theory to direct the practice. In the present dissertation, the effects of tube vibration of the two 2-D circular cylinder on convective heat transfer was investigated, and the flow-induced vibration of the cylinders was analyzed.In the first part, both the static and vibrating cylinders were analyzed at different spacing ratios via the Fluent software to find the relationship between spacing ratios and convective heat transfer of the two cylinders. The field synergy theory was used to analyze the synergy of the velocity and temperature field in different spacing ratios. The results show that there exists a threshold of spacing ratio. When the spacing ratio of the two cylinders is larger than the threshold, heat transfer of the two cylinders enhanced, and vice versa. Therefore, the spacing ratio of the heat exchanger can be L/D>3.5 in the design of heat exchanger.In the second part, the effect of vibration on heat transfer of the two 2-D cylinders was discussed. The vibration direction,the frequency and the amplitude of the oscillating circular cylinders were studied in this part. The numerical simulation results show that the different vibration direction of the cylinders have little effect on heat transfer and the synergy of the velocity field and the temperature field were almost the same; when the frequency and the amplitude increased, the heat transfer of the cylinders enhanced, and vice versa. In the third part, the numerical simulation of flow-induced vibration of the two 2-D cylinders with transverse motion was conducted. The relationship between the magnitude of inlet velocity of the flow and the flow-induced vibration was studied.The numerical simulation results show that the amplitude of the vibration has a maximum with the inlet velocity of the flow equals to 5.676. When the velocity is lower than 5.676, the amplitude was smaller than the max, and when the velocity is larger than 5.676,the amplitude was also decreased.At low inlet velocity, the two 2-D cylinders galloped, and the frequency was smaller than the vortex shedding frequency. When the inlet velocity increased, the beat phenomenon could be discovered on the cylinders, and the frequency of the flow-induced vibration was complex. When the vortex-induced vibration happened, the frequency of the cylinders equaled to the vortex shedding frequency.In the fourth part, the flow-induced vibration of two 2-D cylinders at different stiffness and mass ratios were investigated. The results show that the amplitude of the cylinders increased with the stiffness decreased, and when the stiffness decreased to a level, the amplitude stabilized at a constant. The frequency of the cylinders was smaller than the vortex shedding frequency while the stiffness increased and the vibration becomes more complex. The vibration of the cylinders was harmonic at small mass ratio, and the frequency equaled to the frequency of the vortex shedding. As the mass ratio increased, the amplitude would be lower, and the frequency would be smaller than the vortex shedding frequency, the vibration became more complex.