IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 _______________________________________________________________________________________ Volume: 04 Issue: 01 | Jan-2015, Available @ http://www.ijret.org 443 ANALYSIS OF CROSS-FLOW INDUCED VIBRATION IN AN INLINE AND STAGGERED CONFIGURATION Vimal D. Tandel 1 , Rajesh V. Patil 2 1 PG Scholar, Department of Mechanical Engineering SITS, Pune, Maharashtra, India 2 Asst. Professor, Department of Mechanical Engineering SITS, Pune, Maharashtra, India Abstract In many engineering applications like heat exchanger, radiator, evaporator, nuclear power plant and thermal power plant, arrangement of tubes is very crucial. Fluid elastic instability forms the basis for deciding the type of arrangement and tube spacing but the phenomenon of vortex induced vibration is random in nature. Tube spacing also plays a critical role in different types of arrangement. Different type of application requires different tube spacing and the range of tube spacing vary from 1 to 6. Vortex Induced Vibration in cross flow around the inline and staggered arrangement of the tube arrays is experimentally studied for varying P/d (tube spacing) ratio. It is observed that with the increase in the velocity, the amplitude displacement increases. As the amplitude displacement of the tube reduces, the pitch over diameter ratio is increased from 2 to 4. It is also observed that between inline and staggered arrangement, the amplitude displacement of staggered arrangement is more compared to inline arrangement for same tube spacing. Keywords: Vortex Induced Vibration, Inline Arrangement, Staggered Arrangement, Regression Analysis --------------------------------------------------------------------***---------------------------------------------------------------------- 1. INTRODUCTION The interaction between the fluid flow and the cylindrical structures play an important role in many applications of engineering. Due to its practical importance, flow around the cylindrical structures has been studied. The fluid flow around the cylindrical structures exhibit various physical phenomena like turbulence buffeting, vortex induced vibration, fluid-elastic instability and acoustic resonance which may severely damage the cylindrical structures. In heat exchanger, the cylindrical tubes are placed in close proximity to one another and there are large numbers of tubes. The forces experienced by the cylindrical tubes and the flow field around the tubes are entirely different compared to the single tube immersed in the fluid flow. Vortex induced vibration is the major consideration since heat exchanger are designed keeping in mind the threshold for fluid-elastic instability. Grover and Weaver [10] used a 19-tube array with only one tube flexible and the other was made rigid. They found out that vibrations induced by the fluid flow were responsible for the instability of the single flexible cylinder. They concluded that the mechanism which was responsible for the instability of a single flexible cylinder is the same mechanism leading to the instability of an entire flexible array. Chunlei et al [6] studied numerically the vortex shedding characteristic and forces acting on the tube in an inline cylinder array. They considered flow to be laminar and studied the effect of tube spacing on the array. Computations were carried out for a six row inline tube bank. They concluded that by increasing the spacing makes the flow more asymmetric and induces vortex shedding. Vortex shedding starts from the last cylinder and proceeding upstream. E. Longatte et al. [8] studied the numerical methods for investigating the effects of flow induced vibration on the tube bundle motion in presence of fluid at rest and single phase cross-flows. They used arbitrary Langrange Euler formulation for the fluid computation to simulate thermo-hydraulics and mechanics. The main purpose was to provide a numerical estimate of the critical flow velocity for the threshold of fluid-elastic instability of tube bundle without experimental investigation. They validated their results with the available experimental data obtained with same configuration. S. Pasto [13] performed the experiment on freely vibrating circular cylinder in turbulent and laminar flows. He performed the experiment in the wind tunnel by varying the roughness of the cylinder and mass damping parameter and studied the behavior of the cylinder in terms of Reynolds number. 2. EXPERIMENTAL DETAILS Vortex induced vibration is a very complex phenomena and the vibration amplitude of the tube is affected by many parameters. In order to find out the amplitude displacement of the flexible tube for vortex induced vibration phenomena, many experiments have been performed. In this paper, effect of tube spacing, i.e. pitch over diameter ratio, is found out experimentally. Experiments were conducted on wind tunnel where maximum attainable velocity was 25 m/s. Effect of pitch over diameter ratio has been found out for both the inline and staggered arrangement. Since many applications of engineering lie below the ratio, the pitch over diameter has been selected 2, 3 and 4.The tube end is supported at the top surface of the test section of wind tunnel and the other end is free. Cantilever tube bundles are subjected to air flow. The support has been taken cantilever because natural frequency of cantilever tube is very less as compared to the other type of end supports and hence its stiffness. Thus, it maintains the less difference between the natural frequency and the forcing frequency of the tubes.