Response Of An Elliptical Cylinder In The Wake Of A Circular Cylinder

It is found that the seals can hunt preys with their whiskers to detect the trail left by the preys according to the experiment with the blindfolded harbor seal.It is also found that the elliptical cross-section of whisker plays an important role in detecting wake as well as suppressing force and vibration.Meanwhile,elliptical cylinders are also widely employed in engineering and construction fields,i.e.,tubes in heat exchangers and buildings.This paper mainly studies the vibration response of an elliptical cylinder in the wake of a circular cylinder.Two-dimensional simulations are carried out for the unsteady laminar flow past the elliptical cylinder in the wake of circular cylinder at Re=100.Two arrangements are considered,tandem and staggered arrangement.The effect of L~*and T~*on the wake structure and vibration response is investigated,where L~*is the in-line distance between the center of upstream circular cylinder and downstream elliptical cylinder,T~*is the transverse distance between the center of circular cylinder and elliptical cylinder.A wide L~*and T~*range is included,i.e.,L~*=1.2,2,3,4,7 and 10,T~*=0,0.2,0.6 and 1.0.The downstream elliptical cylinder is allowed to freely vibrate in both in-line and transverse direction.To achieve the obvious vibration,the mass ratio(m~*)is chosen as 10 and damping ratio is zero.The flow field,vibration amplitude,vortex shedding frequency,lift and drag coefficient are studied.For fixed elliptical cylinder in tandem arrangement,three distinct flow structures,over-shoot flow,steady flow and co-shedding flow,are obtained.Moreover,the initial branch(IB),lower branch(LB)and desynchronization branch(DB)characterize the vibration response for all the investigated configurations.An additional branch,‘no vibration branch(NVB)'is detected for L~*=2,3 and 4.The NVB appears when the frequency ratio(fve/fne)?1 for L~*=3 and 4 but fve/fne?1 for L~*=2,where fve and fne is the vortex shedding frequency and natural frequency of elliptical cylinder,respectively.The phenomenon of no vibration gradually disappears with T~*increasing.The vortex shedding frequency and oscillation frequency of the elliptical cylinder are always consistent with the vortex shedding frequency of upstream circular cylinder for the investigated cases.