管道不可压缩流动压力脉动(伪声)的数值研究

Numerical study on the hydraulic pressure fluctuations(pseudo-sound)of incompressible flows in pipes

以直管和90°弯管为对象,研究管道不可压缩流动的水动力压力脉动(伪声)特性。分析了不可压缩流动中压力脉动的Poisson方程,并与波动方程进行了比较;在管道进口处设置随时间正弦变化的压力脉动,使用SST k-ω湍流模型,通过数值求解不可压缩流动的Navier-Stokes方程得到直管和弯管内的脉动流动;比较分析了直管和弯管内的时均流场及脉动流动。结果表明:沿管道流动方向流场压力脉动线性衰减,压力脉动传播整体上呈一维形式,而速度脉动形式紊乱;90°弯头对局部流动影响明显,导致压力和速度脉动均有提高;流场脉动以基频及低次谐波为主,90°弯头导致宽频脉动分量有所提高;归因于压力脉动的椭圆型Poisson方程,扰动的传播速度为无穷大,管道各处压力脉动信号无相位差。

The hydraulic pressure fluctuations(pseudo sound)inside a straight pipe and a curved-pipe with a 90°bend were studied.Firstly,the Poisson equation of the pressure field related to incompressible flow was derived and compared with the wave equation.Then,by solving the incompressible Navier-Stokes equations together with the SST k-ωturbulence model,the unsteady flows inside the two pipes with a sinusoidal pressure boundary condition being applied at the pipe inlet were obtained.Finally,the characteristics of the mean and fluctuating flow fields in the straight and curved pipes were analyzed.The results show that the amplitude of pressure fluctuation decreases linearly along the pipe downstream direction with 1D propagation pattern,while the velocity fluctuation is very chaotic.The 90°bend has obvious influence on the local flow causing the increase of pressure and velocity fluctuation therein.Due to the sinusoidal pressure pulsations at the pipe inlet,the flow fluctuations inside the pipes are dominated by the fundamental frequency and its low-order harmonics,and the 90°bend contributes the broadband fluctuation.Owing to the adoption of the elliptic Poisson equation of pressure fluctuation,the propagation speed of the disturbance is infinite,and there is no phase difference in the pressure fluctuation signals at different locations inside the pipes.