Study On Simulation Of Flow Past Four Side-by-side Cylinders Of Different Diameters

Many phenomena in practical engineering are closely related to the flow around the bluff body,such as chemical reaction tower of power plant,bridge pier,offshore oil exploration platform,high-rise building,flow around fingers,etc.The study of flow around a circular cylinder is a typical case of flow around a bluff body.The flow around one or two cylinders has been thoroughly studied.However,there are few researches on the flow around multiple cylinders.The present study focuses on the effects of diameter ratio D/d(D is the diameter of the inner cylinder,d is the diameter of the outer cylinder)and gap spacing ratio g~*(=g/D_m,g is the gap spacing between two cylinders,and D_m=(D+d)/2)of multiple cylinders on the lift,drag forces and vortex shedding frequencies of cylinders.In the present numerical study,the effect of D/d=0.4-1.6 and g~*=0.25-5 on the flow fields around the four-cylinder system are evaluated by the measurement of fluid flow forces' coefficients((?))and vortex shedding frequencies(f).The Reynolds number Re is 100.With the variation of D/d and g~*,the flow around four cylinders could be classified:single-bluff body flow,chaotic flow,quasi-periodic,periodic flow,and interlocked flow.The complete map of diameter ratio-gap ratio(D/d-g~*)is achieved.Then,the dependence of the (?),(?),C'_D and C'_L of each cylinder and four-cylinder system on g~*and D/d are revealed.For different gap ratio g~*,at D/d=0.8,the CD on the whole four cylinders is the maximum.At D/d=1.3,the CD on the four cylinders is the minimum.There is a sudden decline for CL of cylinder 2 at D/d=1.3 which corresponds to the smallest drag coefficient on the four-cylinder system.The phenomena of the maximum thrust and minimum thrust occurring at D/d=0.8 and 1.3 are observed and explained in comparison with that at D/d=0.6 and 1.0 for g~*=0.5 and 2.0.Furthermore,to obtain the maximum thrust,the condition could be taken into account and applied.