Numerical Simulation Study On Influence Of Rods On Cylindrical Vibration And Wind Energy Collection Characteristics

In the past few years,energy harvesting and utilization have attracted substantial attentions and a large amount of studies.Wind energy harvesting based on wind-induced vibrations of bluff bodies is one of the most popular branch of energy harvesting.Increasing the vibration of bluff body has been proved to be an effective way to enhance performance of wind energy harvester.In this study,small-scale rods were attached on the main circular cylinder.The effects of attached position,shape,and size of rods on aerodynamic characteristics,wind-induced vibrations,and efficiency of energy harvesting were studied by using computational fluid dynamic simulations.In addtion,performance of energy harvesting by multiple cylinders in series was assessed.In terms of behaviors of separated shear layers,specifically whether the shear layers reattached on the cylinder or not,the cylinder with rods can be classified into two groups.For the first group,the attachment angle was small including 15° and 30°.Reattachment of the shear layers occurred,lift and drag decreased,and Strouhal number increased slightly.For the second group,the attachment angle is larger and ranges from 45° to 90°.The reattachment does not occur.Lift and the energy of vortex shedding increase,and the case with triangular rods is more easily affected by the attachment angle.To understand the fluid-struture interaction behaviors of the aforementioned cylinders,the wind-induced vibration of the cylinders was simplified as a single degree of freedom spring damping system,and the efficiency of energy harvesting under various conditions were studied.For the first group,the lock-in region and the maximum amplitude were reduced,and the wind-induced vibration of cylinder was obviously suppressed.Compared with a plain cylinder,the amplitude and generated power for the second group were greatly increased,among which the case with ?=60° exhibited the best performance.When two cylinders were placed in series,except for the case with ?=30°,vibrations of the upstream cylinder were increased by the downstream cylinder.For the other cases,the power,amplitude and frequency of the upstream cylinder basically remained unchanged as the corresponding single cylinder.For the downstream cylinder,the vibration characteristics are greatly affected by the wake of the upstream cylinder.The amplitude and generated power of both plain cylinder and the case with ?=30° are much higher than that of the upstream cylinder,which is inversely proportional to the interval between the two cylinders.For the second group,the dimensionless power of downstream cylinder approached or even exceeded that of the upstream cylinder when the reduced velocity is larger.Compared with the capability of energy harvesting of three cylinders in series,it was found that with increasing the number of cylinders,the average power of plain cylinder and the case with ?=30° increase.For the second type of working conditions,the average power in the low speed zone is reduced.The total power distribution of each working condition can be divided into three regions.When the reduced velocity is low,the total power of each condition is similar.While the total power of plain cylinder is the largest,when reduced velocity is medium.When reduced velocity is high,plain cylindrical condition due to "self-limiting",the total power is rapidly reduced to maintain a low level The total power of the ?=60° working condition is greatly increased and increases with the increase of the number of series,and the overall trapping effect is the best.