Study On The Fluid And Acoustic Field Of Gas-Liquid Two-Phase Flow In Pipe

In the engine exhaust pipe, cooling the waste gas down by spraying water can change thedensity and temperature of the gas. And then, the gas impedance is also changed, so partialexhaust noise can be reflected on the propagation process. In addition, the friction producedby the gas-liquid mixing process can deplete the energy of the noise as well. They are bothbeneficial for reducing the exhaust noise. Therefore, it’s extremely significant to study thefluid and acoustic field in the engine exhaust pipe with water spraying.Firstly, the basic theories on acoustics of two-phase pipe flows were studied. The soundspeed formula in the water hammer theory was rewritten in another form which was related tothe variation of the flow cross-section upon the propagation of the pressure disturbance. Fromthis new form sound velocity formula, the expression of the gas and liquid phase sound speedin stratified and annular flow were derived. The acoustic velocity of the two phases changelaws relating to void fraction were obtained. In cylindrical coordinates, based on the theory ofthe acoustic waveguide in pipe and the computational method of the cut-off frequency insingle phase flow, the cut-off frequency of the gas phase in annular flow was calculated, bythe boundary condition that normal velocity and pressure across the interface werecontinuous.By researching on the differences among all kinds of two-phase fluid calculation modelsin CFX, including fluid morphology, heat transfer and momentum transfer, the simulationmethod for the water spraying process was founded. Numerical simulation of engine exhaustprocess with water spraying was achieved. The distribution of gas-liquid two-phase volumefraction, temperature, velocity and pressure in the pipe was obtained. According to thecomputing results under different cooling water flow rates, the change laws of the gastemperature and velocity were analyzed.For the acoustic field in the exhaust pipe of the engine with water spraying, flow noisecalculating method with CFX and Virtual. Lab Acoustic was applied to simulate acousticfield in the pipe. The numerical simulation of the acoustic field of the low liquid volumefraction gas-liquid two-phase flow in pipe was achieved. And the distribution characteristicsof acoustic field in the pipe were obtained. At the end of this paper, water spraying imitation experiment system was set up tomeasure the acoustic pressure at different position and cooled gas temperature. The influenceson acoustic filed in the gas-liquid two-phase pipe were studied. And the positive effect of thespraying water on reducing the noise in the pipe was proved at the same time.