EXPERIMENTAL AND NUMERICAL INVESTIGATION OF VORTEX-INDUCED VIBRATIONS AND PRESSURE DROP IN SQUARE PIPE WITH OBSTACLE
Kadhum Audaa Jehhef1, Mohamed Abed Al Abas Siba2
1Department of Mechanical Power, Institute of Technology, Middle Technical University, Iraq.
2Department of Mechanical Power, Institute of Technology, Middle Technical University, Iraq.
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In this paper, a study on the fluid vortex-induced vibration caused by an obstacle used as vortex generator inserted in a square pipe is conveying a water flow with laminar and turbulent flow condition has been considered. The water flows in the pipe with length of L=1000 mm and side length a=20 mm. The obstacle located in the middle section of the duct with height to duct side ratio given by (h/a) as 0.0, 0.25, 0.5 and 0.75. The flowrate of the water that enter to the pipe with Reynolds number that varied by 860, 1300, 1700 and 2100 for the laminar flows and with range of 3500, 430, 5200 and 6900 for turbulent flow. The time history signals of the structure vibration accelerations measured by the accelerometer. Simulation is carried out by using ANSYS-FLUENT to solve the Navier-Stokes equation by adopting k-ε turbulence model. The experimental results are given by natural frequency of the free vibration signals of the pipe structure of the test section. The results indicated that the using an obstacle lead to increase the pipe frequency. As a result, flow induced vibration is also observed at moderately in high Reynolds numbers. The results obtained by experimental tests indicated there is a strong effect of the Reynolds number on the vibration signal. These vibration signals are believed to be caused by friction coupling between the fluid and the wall pipe in the case of smooth pipe and by vortex generated due to the obstacle. The frequency is the highest values at the case of high ratio of obstacle due to high fluid velocity and pressure changes across the obstacle. Finally, the results show that the obstacle heights have a significant effect on the pressure drop.