In a recent investigation experimental measurements of the particle pressure for solid-liquid flows were obtained. The particle pressure was defined as the additional pressure exerted on the containing walls of a particulate system due to particle collisions. The particle pressure measured on a surface was found to be composed of two contributions: direct collisions of particles against the surface, and a pressure contribution from particle-to-particle collision that was transmitted through the fluid. The present article presents an investigation of the pressure generated by a particle-particle collision that is transmitted through the fluid moments after impact occurs.
Experiments involving binary collisions of particles were performed. A simple dual pendulum was set up to generate controlled collisions. A particle was positioned at rest (the target particle) at a certain distance from a wall. On the wall a high-frequency-response pressure transducer was flush mounted. A second particle (the impactor particle) was relased starting from rest at some initial angle. The particle accelerated towards the other particle and produced a collision. When the two particles came into contact, the impulsive acceleration imposed on the target particle produced a pressure pulse, which was transmitted through the fluid from the point of impact to the pressure transducer. To characterize the nature of this pressure front, measurements were obtained for a range of impact velocities, angles of incidence, and distances away from the wall for different pairs of particles. The motion of both particles was recorded using high speed digital camera.
The results show that the peak pressure of the front decreases with the distance from the wall. The pressure raise corresponds with predictions from simple fluid mechanics considerations. The strength appears to scale with the particle impact velocity and the density of the fluid.