An experimental measurement research on impact load of high speed water jet acting on a rigid target by a Hopkinson pressure bar

Abstract

A high speed water jet generation device based on explosion in a cylindrical cavity is introduced, which can eject a well-characterized water jet with a velocity around 100 m/s. The evolution characteristics and impact phenomenon of water jet act on a rigid target are observed by a high speed camera and the impact load is measured by a Hopkinson pressure bar. The top shape of water jet develops from a convex spherical surface to a flat plane as the stand-off increases under the influence of air resistance. When the top of water jet contacts the target plate, a transient high-pressure zone appears at the liquid-solid interface. A horizontal annular splashing jet generates and the velocity of splashing jet is much higher than that of incident jet as the result of high-pressure zone. The impact load is measured by the Hopkinson pressure bar, including transient “water hummer” pressure and subsequent hydrodynamic load. The “water hummer” pressure of water jet with a flat top is twice that with a convex spherical top, while the subsequent hydrodynamic pressure is equivalent at a comparable transient impact velocity. The measurement results by a Hopkinson pressure bar are in good agreement with the theory formulas in terms of both “water hummer” pressure and hydrodynamic pressure. It is certified that the Hopkinson pressure bar has a credible measuring capacity for both transient and steady-state pressure. By controlling cavity depth, charge amount and stand-off distance, the different top shape and velocity of water jet can be obtained.