Effects of Nozzle Exit Angle on the Pressure Characteristics of SRWJs Used for Deep-Hole Drilling

The self-resonating waterjet (SRWJ) has been applied in petroleum, natural gas, and mining engineering ever since its strong erosion ability in deep-hole drilling was recognized. Aiming at further improving the working efficiency of SRWJs, the effects of the exit angle of the organ-pipe nozzle on the axial pressure oscillations of the jet were experimentally studied. Six exit angles of θ = 0°, 30°, 45°, 60°, 75°, and 90° were employed in the experiment, and the axial pressure oscillation peak (Pmax) and amplitude (Pa) were used for characterizing the performance of SRWJs. It was found that the exit angle greatly affects the axial pressure oscillations, including the development trends against the standoff distance and the magnitudes of Pmax and Pa. Under testing with two inlet pressures, the exit angle of θ = 0° always resulted in the greatest Pmax and Pa within the range of the testing standoff distance. With the increase of standoff distance, both Pmax and Pa first increased and then decreased when the exit angle was 0°; while they kept decreasing when the exit angle was 30°, 45°, 60°, 75°, and 90°. Moreover, the exit angles of θ = 90° and 60°, corresponding to inlet pressures of Pi = 10 MPa and 20 MPa, led to both the minimum magnitudes of Pmax and Pa under the experimental conditions. The results also indicate that the exit angle affects the interactions between the nozzle lip and the jet and help provide information for improving the working efficiency of SRWJs in practical applications.