Characteristics of Oscillation in Cavity of Helmholtz Nozzle Generating Self-excited Pulsed Waterjet

Abstract

Cavity flow oscillations in the axisymmetric cavity are critical to the operating efficiency of self-excited pulsed waterjets, which are widely employed in many practical applications. In this study, the behaviors of a turbulent flow in axisymmetric cavities causing cavity flow oscillations are investigated based on wall pressure characteristics. Experiments are performed using four Helmholtz nozzles with varying length-to-radius ratios at flow velocities of 20–80 m/s. Three orders of hydrodynamic modes in axisymmetric cavity are obtained through the spectral analysis of wall pressure. Based on the experimental results, the empirical coefficient of Rossiter’s formula is modified, and the values of the parameter phase lag and the ratio of convection velocity to free stream velocity are obtained as 0.061 and 0.511, respectively. In addition, the spectral peak with a relatively constant frequency shows that the flow-acoustic resonance is excited significantly. A modified model is introduced based on the fluidic networks to predict the lock-on frequency. The results obtained can provide a basis for the structural optimization of the nozzle to improve the performance of self-excited pulsed waterjets.

Study on Mechanism and Regularity of Rock Breaking by Pulsed Water Injection with Particles

“…Water jet [19,20] Improves rate of penetration and bottom-hole purification effect, reduces rock-holding effect and avoids repeated drill bit damage, High power consumption and short nozzle life Deep and ultra-deep rock have a compact texture, high wear resistance, and high compressive strength, thus aggravating the wear of the bit, reducing drilling efficiency, and seriously restricting the speed and cost of oil and gas exploration and development. With the development of modern science and technology, some new rock-breaking technologies have emerged.…”

“…Water jet [19,20] Improves rate of penetration and bottom-hole purification effect, reduces rock-holding effect and avoids repeated drill bit damage,…”