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

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 (P_max) 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 P_max 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 P_max 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 P_max 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 P_max and P _a against the dimensionless standoff distance are linear and cubic, respectively. In addition, the dimensionless P_max 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.