Research On Characteristic Of Aerodynamics For A Smooth Cylinder In The Critical Reynolds Number Range

Circular cylinders are widely used in civil engineering.Wind induced large-amplitude vibration often occurs in slender structures with circular cross-sections.This kind of structure in large amplitude vibration when the Reynolds number is often enter the critical Reynolds number range,therefore,the critical Reynolds number range is one of the important factors influencing the stability of slender cylindrical structure gas.The most testing models are a sectional model because of the limitation of wind tunnels.Therefore,the aspect ratio is a significant parameter in aerodynamic forces tests in wind tunnel.this dissertation adopts rigid model wind tunnel test and elastic suspension synchronous pressure measurement wind tunnel test,to study the influence of dynamic characteristics of long and thin comparison of gas cylinders in cylindrical and critical Reynolds number range of the static and dynamic aerodynamic characteristics,mainly including the following aspects:(1)Effects of aspect ratios on the aerodynamic characteristics for a smooth cylinder.The local aerodynamic forces at the middle of the cylinders in the subcritical,critical and supercritical Reynolds number were measured for several models with various aspect ratios through the pressure measurement on rigid section models in the wind tunnel.(2)The three-dimensional characteristics of the static aerodynamic distribution of a smooth cylinder in the critical Reynolds number range.The three-dimensional characteristics of cylinder under different Reynolds numbers are analyzed,including the flow pattern,vortex shedding process and fluctuating pressure.(3)The dynamic aerodynamic distribution characteristics of a smooth cylinder in the critical Reynolds number regime.The dynamic aerodynamic characteristics of a smooth cylinder in critical regime are analyzed,and the reason for the large amplitude vibration of the cylinder in critical regime is analyzed.Through the analysis of the test results,the following conclusions are drawn:(1)In the subcritical and supercritical regime,for a finite length cylindrical model with 4 times diameter end plate,the aerodynamic characteristics of the span are not continuous with the variation of the length to slenderness ratio.In the critical regime,the aerodynamic test results in the column span are less influenced by the length and fineness ratio in a certain Reynolds number,and show a stronger three-dimensional characteristics;(2)The three-dimensional characteristics of the static aerodynamic distribution of a smooth cylinder in the critical region are characterized by the difference in the vortex shedding process,the intensity of fluctuating wind pressure and the flow state.(3)The reason for the large vibration of the slender cylindrical structure in the critical regime is the large average lift caused by the separation bubble on the smooth cylinder side,and the intensity of the fluctuating wind pressure in the range of the bubble is also one of the important factors.