壁湍流边界层奇异标度律的实验研究

Anomalous Scaling Law in Turbulent Boundary Layer

采用热线风速仪对平板湍流边界层的流向速度进行测量,用速度结构函数研究不同尺度结构标度律的变化规律,结果显示小尺度区的概率密度曲线尾部明显偏离高斯型,说明高幅值间歇性事件占的份额较多;惯性子区的曲线向高斯型靠近,间歇性事件所占份额减少;大尺度结构的曲线趋于高斯型,间歇性事件所占份额最小。在耗散区、惯性子区和较大的尺度结构区存在大小不同的绝对标度指数,越靠近壁面这些区域的标度指数均越偏离p/3而逐渐变小。绝对标度指数与边界层位置有关,在缓冲层各阶标度指数与线性标度律偏差很大,显示较强的奇异性,当过渡到对数层及外区,标度指数逐渐增大,接近均匀各向同性湍流的状态。缓冲层、对数层及外区具有各异的绝对标度指数增长率,与各层的不同湍流结构特征和运动形式有关。

The velocity time sequence in the turbulent boundary layers was finely measured by IFA300 constant-temperature anemometer. Variable rules of scaling law were studied by using structure functions. Different characters of probability density curves are obtained. The predominate intermittent events in small scales result in the graphics deviating from the Gauss curve. With decreasing intermittent events in inertia scales the curves close to the Gauss graphics. Large scale possesses the least intermittent events and its graphics fits to the gauss line well. Different scaling exponents exist in dissipative region, inertial region and large scale region respectively. The more a position is cloce to the wall, the smaller the scaling exponents tend to and deviate from the law of p/3. The absolute scaling exponents have relation with the position of the boundary layer. In buffer layer all exponents deviate from linear scaling law which expresses the significant singularity. Along with the boundary layer diverts to the logarithmic area or even to the outside of boundary layer, the scaling exponents gradually increase until add up to the value of homogenous turbulence. Each absolute scaling exponent in buffer, logarithmic and outside areas denotes respective ascending rate which refers to distinct turbulent structures and movements in different layers.