Effects of the exit aspect ratio of organ-pipe nozzle on the axial pressure oscillation characteristics of self-resonating waterjet

Abstract

Self-resonating waterjet is a kind of high-efficient jet being employed in a number of applications. This study aims to enhance the working performance of self-resonating waterjet by providing organ-pipe nozzles with the optimal exit aspect ratio R o. The characteristics of the axial pressure oscillation of the jets were analyzed with the use of six different R o, which were R o = 2, 2.5, 3, 4, 5, and 6, respectively. The pressure oscillation peak ( Pmax) and amplitude ( P a) were used to evaluate the effects under two inlet pressures of 10 MPa and 20 MPa. Results show that R o has significant influence on the magnitudes of the pressure oscillations and is able to eliminate the self-resonating pulsations. It was found that both Pmax and P a as a function of the standoff distance shows some differences for different R o, while the inlet pressure is almost independent of the trends of Pmax and P a against the standoff distance for all the six R o. Under the experimental conditions, R o = 5 should be the optimal ratio for creating the largest Pmax and P a. While at inlet pressure of 20 MPa, R o = 4 turns to be a preferred value for generating greater values of the P a. It was also found that the relations of the averaged dimensionless Pmax and P a against the dimensionless standoff distance are linear and cubic, respectively. In addition, the dimensionless Pmax against R o is hardly affected by the inlet pressure and standoff distance, while the dimensionless P a as a function of R o is influenced by the standoff distance more than by the inlet pressure.