Particle Velocity Measurement In Swirl Flow, Laboratory Studies

Abstract

This paper presents the laboratory studies of particle velocity measurement in highly swirl conditions similar to turbine flow in curved path. It includes a brief description of the developed test rig, concept of critical diameter of particle inside a Francis turbine and experimental analysis. When a particle is flowing in swirl flow, drag force and centrifugal force are two major forces influencing the particle equilibrium. The equilibrium of these two forces provides a critical diameter of the particle. While, a particle larger than the critical diameter move away from the centre and hit the wall, a particle smaller than the critical diameter flows along with the water, and ultimately sinks. For critical diameter, the particle continues to rotate in the turbine. Different shapes and sizes of particles were tested with the same operating conditions and found that triangularly shaped particles were more likely to hit the suction side of the guide vane cascade. Furthermore, this study supports the concept of separation of particles from streamlines inside the test rig, which led to the development of an operating strategy for a Francis turbine processing sediment-laden water. This study also permitted experimental verification of the size and the shape of a particle as it orbits in the turbine, until either the velocity components are changed or the particle became smaller.