循环射流混合槽内瞬态压力波动非线性标度特性

在湍流状态下(Re=3660~32940)利用动态数据采集系统对新型循环射流混合槽射流混合区内不同轴向、径向和周向位置的瞬态脉动压力进行测量，研究了压力波动的湍动能量及其时间结构函数的扩展自相似标度律. 基于压力波动信号的递归率和能量分布特点，确定瞬态压力波动分析的初始优化参数. 结果表明，数据长度n≥80000时，时间序列的波动能量趋于稳定且相对变化率低于0.3%，其对数值与雷诺数存在线性关系；瞬态压力波动的q阶与3阶时间结构函数的双对数存在线性关系，同时波动信号的q阶时间结构函数的标度指数x(q)小于同阶时间结构函数相对标度指数x(q, 3)，相对标度指数x(1, 3)和x(5, 3)[或x(2, 3)和x(4, 3)]关于x(3, 3)对称分布，q≥4时相对标度指数x(q, 3)随极角q增加而增大；q<3的相对标度指数x(p, 3)随r/R和qm的变化与q≥4时的相对标度指数分布相反.

Non-linearity of Scaling Law of Instantaneous Pressure Fluctuation Signals in a Circulating Jet Tank

In order to reveal the nonlinearity of fluid system in the mixing zones of a circulating jet tank, a high-speed acquisition system was employed to measure the instantaneous pressure fluctuation signals at different axial, radial and circumferential positions in turbulent flow region with a range of Re between 3660 and 32940. Both the amplitudes of fluctuation energy and scaling law of extended self-similarity for the structure function of pressure signals were evaluated. The initial parameters on sampling frequency and data length of pressure time series were optimized based on the recurrence rate and amplitudes of fluctuation energy. The experimental results indicated that the relative increasing ratios of amplitude of fluctuation energy were below 0.3% and a linear relationship between logarithm values of amplitude of fluctuation energy and Re existed when the date length was not less than 80000. The logarithm values between the qth- and third-order time structure functions of pressure signals were in accordance with a linear relationship. The scaling exponent x(q) of time structure function was smaller than relative scaling exponent x(q, 3). The profiles of relative scaling exponents x(1, 3) and x(5, 3) [or x(2, 3) and x(4, 3)] were symmetrically distributed about the profile of x(3, 3). The relative scaling exponent x(q, 3) was enlarged with the increase of qm when the order value of q was equal or greater than 4. But the distribution of x(q, 3) was contrary with the increase of polar angle q or r/R when the order value of q was less than 3.