Study On Water Hammer Characteristics Of Coarse - Grained Solid - Liquid Mixture In Pipe Flow

In hydraulic transportation system, power failure or by mechanical fault can cause the velocity and pressure instantaneouschange.So water hammer will destroy pipeline seriously. Fortwo-phase solid-liquid flow with coarse particles, the following behavior is bad and the momentum transfer between fine particles and coarse particles is different when waterhammer happen. Based on Particle Image Velocimetry(PIV)、Particle Tracking Velocimetry (PTV) and pressure testing system, the paper analyze the characteristics of coarse particles in pipe particle following behavior and the changing pressure of waterhammer. The conclusions are as follows:(1)Through PIV collecting the date, particle velocity with 0.1mm diameter at the pipe center are the fastest, and at the bottom and the top are the slowest. The velocity distribution curve calculated by the empirical formula and the curve by experiment have the same tend. When average flow velocity is 1.0m/s, calculated value is slightly higher than measured value. When the average flow velocity is 1.5m/s and 2.0m/s, calculated value is almost coincident with the test value. This shows that 0.1mm particle have good following behavior.(2)Through PTV collecting the date, regarding pipe center point as base point, particle velocity distribution in the pipe section is exponential form, which accord with empirical formula of the turbulent flow in pipe. Particle velocity at the bottom of the pipe is lower than at the top. The bigger particle size, the worse particle following behavior when the average velocity are the same. The greater the average velocity, the better particle following when particle size are the same. When flow velocity is larger, flow resistance near the pipe may increase which lead to the coarse particle velocity bigger than water velocity. To explain the particle in the pipe cross section distribution asymmetry, the paper select three points’particle velocity on the section, and fit the data. The fitting formula’calculated value is close to measured value and maximum error is less than 6.4%. Particle following behavior is complex on the pipe section. So the paper analyze particle following behavior and fitting result is relatively good.(3)Combined with PTV and pressure test system, the paper analyze particle following behavior and pressure change in the process of water hammer. The results show that particle velocity change gradually smaller when water hammer happen and particle velocity distribution in pipe section is exponential distribution. Because of gravitational effects, particles gradually deposit on the bottom of the pipe wall. Particle size and water flow velocity have.great effect on particle following behavior. The bigger particle size or the smaller water flow velocity, the worse particle following behavior. Because of particle volume concentration lower, particle size is not obvious influence on water-hammer pressure. But increase of flow velocity strengthen turbulence effect of the flow Then the wave crest length and duration increase correspondingly.