Aerodynamic Properties And Wind-induced Vibration Of Square Cylinder With Aerodynamic Treatments

Aerodynamic optimization of bluff bodies for controlling their wind-induced vibrations has a wide practical engineering application.On one hand,for civil structures,aerodynamic optimization can effectively reduce wind-induced vibration and hence improve structure security and human comfort.On the other hand,the aerodynamic optimization can effectively enlarge wind-induced vibration response and hence improve the efficiency of wind energy harvester,on which a number of studies were concentrated in the past few years.In this thesis,two optimization strategies are investigated,i.e.installing fins at corners of square cylinder and installing wind turbine at the corners.Aerodynamic characteristics of the optimized square cylinder were studied and the related mechanisms were revealed via computational fluid dynamic(CFD)simulation technique.The effect of corner fins on aerodynamic characteristics of a square cylinder was evaluated via Large Eddy Simulations(LES).Three types of corner fin configurations,i.e.fins fitted only to the leading corners,fins fitted only to the trailing corners,and fins fitted to both leading and trailing corners were studied.Leading edge fins increase mean drag substantially while trailing edge fins reduce it less significantly.The four-fin case is a result of the effects of leading and trailing edge fins,and meanwhile it has a larger mean drag coefficient than the plain cylinder.Similar to effects of the fins on the mean drag,leading edge fins increase the RMS lift coefficient,whereas trailing edge fins decrease the coefficient remarkably.Furthermore,leading fins lead to an obviously lower frequency but much higher energy in the vortex shedding process,while trailing fins result in a slightly smaller frequency but much lower energy in the process.Overall,increasing the fin length simply enhances these effects.Additionally,the square cylinder was simplified as a two-dimensional spring-damping system to study crosswind vibration of a square cylinder with corner fins.It was found that leading fins increase the amplitude of crosswind vibration,while trailing fins decrease the amplitude of crosswind vibration.Increasing the fin length and fin angle enhance these effects.Another aerodynamic modification strategy,i.e.,installing wind turbine at the corner of square cylinder,was investigated via CFD simulation technique as well.First,aerodynamic characteristics of a stationary square cylinder with wind turbines at corners were studied by using LES.Second,crosswind vibration of a square cylinder with wind turbines at corners was simulated via RANS model.The simulation results show that wind turbines at corners of the square cylinder decrease both mean drag and the RMS lift coefficient substantially while increase Strouhal number of the cylinder.Moreover,both the lift and drag coefficients change with wind turbine rotating velocity nonlinearly.Nevertheless,there is a certain rotating velocity to achieve the optimal aerodynamic optimization.In addition,the square cylinder was simplified as a two-dimensional spring-damping system to study crosswind vibration characteristics of square cylinder with corner wind turbines.It was found that corner wind turbines are capable of reducing crosswind vibration amplitude and meanwhile there is an optimal rotating velocity.