稳态背景流场下超声波流量计内瞬态声场分析

Transient analysis of acoustic characteristic in ultrasonic flowmeter under stationary background flow

采用Runge-Kutta间断有限元(RKDG)方法对一款Z型超声波水表进行三维数值模拟,计算过程分为流场计算和声场计算两个部分。采用标准k-ε模型获得超声传播的稳态背景流场。对声学变量作线性化假设,从欧拉方程、连续性方程和状态方程中获得绝热状态下声传播的控制方程。在发射换能器的端面定义法向速度边界条件,以图形化的形式展现超声波在顺流情况下的传播过程。切换发射和接收换能器的相对位置,重新计算得到声波逆流传播时相应接收换能器端面的平均声压分布。对比顺、逆流情况下换能器端面平均声压分布,通过曲线拟合得到的传播时差值要小于实验得到的时差值。该方法为模拟声波在复杂结构和流动中传播提供可能性。

The RKDG（ Runge-Kutta discontinuous galerkin）method that is the combination of discontinuous galekin method for space discretization together with an explicit Runge-Kutta approach for time derivatives has been adopted to show the 3D simulation of a Z type ultrasonic flowmeter in water flow measurement field, which divided into flow field and sound field. Based on the stationary background meanflow obtained by solving the standard k - e model, the control equations are derived from continuity, momentum, and equation of state to describe the propagation of linear acoustic wave in an adiabatic way. The acoustic characteristic is shown in figure when it moves in the direction of the main flow with the presence of a background flow by defining the normal velocity on the surface of transmitter. Through the recalculation, the average sound pressure on corresponding surface of receiver under upstream propagation can be generated by simply switching the source and receiver boundary, as the difference in travel times by comparing the average sound pressure for downstream and upstream propagation which is lower than experimental result. This numerical methodology opens the possibilities in simulating acoustic propagation in other complex configurations, as well as complicated flows.