بررسي عددي و تجربي برهمكنش سيال-جامد با در نظرگرفتن اثر سطح آزاد

چكيده انگليسي :

Numerical and Experimental investigation of Fluid Structure Interaction FSI with consideration of free surface Omid Nazempour o nazempour@me iut ac ir 2012 2 25 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Ahmadreza Pishevar apishe@cc iut ac irSupervisor Shahriar Mansurzadeh shahriar@cc iut ac irABSTRACTVibration and noise problems due to fluid flow occur in many industrial plants These flow relatedphenomena are known as Flow Induced Vibration FIV One of the usual mechanisms of Flow inducedvibration is shedding of vertices behind the bluff bodies This kind of flow induced vibration is known as Vortex induced vibration VIV VIV has important effect on increase the drag coefficient of bluff bodies In this work the flow induced vibration of tethered sphere was investigated Experimental study of thiswork was carried out at towing tank of subsea R D center of Isfahan University of technology Inexperimental study effect of relative submergence of sphere and change of natural frequency of tetheredsphere and variation of Reynolds number on in line and transverse force exerted by the flow was measured Changing the natural frequency of tethered sphere was carried out by changing the length of tether Effectof changing the natural frequency was investigated by using three various length of tether By changing thenatural frequency of tethered sphere kinematic of movement of sphere will be change and in line andtransverse force exerted by the flow will be change Experimental and numerical study was carried out inthe range 105 Re 2 8 105 of Reynolds number In this range of Reynolds number the wake of sphere isfully turbulent and boundary layer on sphere experience transient from laminar to turbulent Fluid Structureinteraction FSI simulations are carried out to investigate vortex induced vibration of elastically tetheredsphere by coupling most famous commercial Computational Fluid mechanics CFD codes ANSYS CFXand finite element code ANSYS Structural Turbulent flow around sphere was simulated using Shear StressTransport Scale Adaptive Simulation model SST SAS that have suitable accuracy for prediction ofseparation flow and low computational cost compare with Large Eddy Simulation LES model Innumerical study in line and transverse force exerted due to fluid flow calculated and compare withexperimental result In addition to variation of frequency of forces with Reynolds number was compared Kinematic of movement of center of sphere was investigated and displacements of center of sphere in bothin line and transverse direction of flow were calculated Wake structure of oscillating sphere was simulatedand compared with non oscillating sphere Two distinct mode of vortex induced vibration of sphere wasobserved that separated with non periodic transitional regime In transitional regime between two vibratingmodes trajectory of movement of center of sphere becomes chaotic and amplitude of oscillation of sphereincrease In first mode of vibration of sphere displacement of center of sphere in both direction are periodicand trajectory of sphere is elliptic With increase the Reynolds number displacement of sphere in in linedirection will be increase The frequencies of exerted forces in both directions are near the naturalfrequency of tethered sphere In transition regime of two mode of vibration the frequencies of exertedforces in both directions decrease whereas frequency of oscillation of sphere remains near natural frequencyof sphere Key words Flow induced vibration Fluid structure interaction Turbulence Vortexshedding Free surface

ناظم پور، اميد

بررسي عددي و تجربي برهمكنش سيال-جامد با در نظرگرفتن اثر سطح آزاد

نوسانات القا شده توسط جريان سيال , جريان مغشوش , رزونانس