טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentDubrovsky Alexander
SubjectFluid-Structure Interaction of Tethered Elliptic
Cylinders in Low Mach and Reynolds Numbers
Two-Dimensional Flow
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Oded Gottlieb
Professor Emeritus David Degani
Full Thesis textFull thesis text - English Version


Abstract

The current work investigates the planar vortex-induced vibration (VIV) response of circular and elliptic cylinders restrained by two elastic tethers, where the nonlinear structural restoring force is derived via a Lagrangian approach and consistently incorporates both streamwise and transverse displacements and rigid-body rotations. The problem is solved numerically by the Beam-Warming algorithm for a two-dimensional compressible flow, with low Mach and Reynolds numbers. The flow is assumed laminar and two-dimensional. Validation of the numerical solver is performed for both fixed circular and elliptic cylinders and for the elastic system of a circular cylinder with linear springs at Re=100. Our numerical investigation of the circular cylinder with finite rigid-body rotations reveals the existence of an additional branch of interlaced quasiperiodic and non-stationary solutions for a large reduced velocity (U*>8) which does not appear in computational results from theoretical models without rigid-body rotation. Investigation of the influence of aspect ratio Γ=b/a (where b is the minor radius and a is the major radius of the ellipse) reveals that the VIV response with a small ratio begins at lower values of the reduced velocity than that documented for the lock-in region of an elastically tethered  circular cylinder. Investigation of the influence of angle of attack α (angle between the direction of the free stream and the x axis) reveals a strong dependence of the VIV response on this parameter. Primary and secondary lock-in regions were found for α>0°.