摘要
The wake of a two-dimensional rotary oscillating plate of chord to thickness ratio B/H=3.0 was investigated by smoke wire visualization and hot-wire measurement in a wind tunnel at Re=1500 and oscillation amplitudes and reduced frequencies in the ranges ofα=2.5°-50°and f_(e)H/V_(∞)=0.02-0.25,respectively,where fe is oscillation frequency,V_(∞) is on-coming wind speed.There are six modes of synchronized vortex shedding observed,including three new modes,i.e.,3P—three vortex pairs shed in one period,2S_(2)—two pairs of vortex twins shed in one period,and T—three vortices shed in one period of plate oscillation.The zone of every mode was found out and drawn on the amplitude-reduced frequency plane.Numerical simulation was carried out,and the simulated vorticity field,velocity profiles,and wake width were verified by experiment at typical oscillation conditions.At higher oscillation frequencies,the linear local unsteady term of inertial force dominates,and the simulated moment is an accurate linear function of rotary displacement and angular velocity.At lower frequencies,where 2T,3P,and 2S_(2) modes of vortex shedding occur,however,the nonlinear convective term of inertial force dominates,and the simulated fluctuating moment deviates from Scanlan’s expression.Statistical results of numerical data show that the root-mean-square(r.m.s)value of fluctuating moment is an exponential function of single parameter η=αf_(e)H/V_(∞).
在风洞中采用烟线流动显示和热线测量方法对弦厚比B/H=3.0的二维旋转振荡矩形板尾流进行了实验研究,研究的雷诺数Re=1500,振幅范围和折算频率范围分别为α=2.5°~50°和f_(e)H/V_(∞)=0.02~0.25,其中f_(e)为振频,V_(∞)为来流速度.发现了6种同步旋涡脱落模式,其中包括3种新的模式:3P模式,一个振荡周期内有三对转向相反的旋涡脱落;2S_(2)模式,一个周期内每侧各有一个同向涡对脱落;T模式,一个周期内有三个涡脱落.找出了每个旋涡模式的存在区域,并在振频-振幅平面上画出了模式区域图.进行了数值模拟,一些典型状态下所模拟的涡量场、速度剖面和尾流宽度,均与实验结果对比而得到了验证.当振频较高时,惯性力中线性的当地非定常项起决定作用,模拟的扭转力矩是板旋转位移和旋转角速度的线性函数.然而当振频较低时,在不同振幅下分别存在2T、3P和2S2模式旋涡脱落,惯性力中的非线性对流项起主要作用,模拟的脉动力矩偏离Scanlan公式.数值模拟数据的统计结果显示,脉动力矩均方根值是单参数η=αf_(e)H/V_(∞)的指数函数.
基金
supported by the National Natural Science Foundation of China(Grant No.11572305).
