Abstract
In order to solve the incompatibility between the diameter and the depth of borehole in high-pressure jet drilling, a novel nozzle that incorporates both advantages of a round straight jet and a swirling jet was designed. The flow field structure and rock breakage characteristics were investigated in experiments for these three nozzles, which generate round straight jet, swirling jet, and straight−swirling integrated jet respectively. Meanwhile, three-dimensional flow fields were simulated for these three jets in terms of a k-ε turbulent model. The results reveal that the straight−swirling integrated jet has features of both a round straight jet and a swirling jet, inheriting both the deep penetration of a round straight jet and the large impact area of a swirling jet, but with larger hole diameter than the round straight jet and greater depth than the swirling jet. The axial velocity of the integrated jet has no potential core compared with a round straight jet, but is much higher than a swirling jet without a protrusion left at the bottom of the drilling hole. The tangential velocity of the integrated jet showing a radial M-shape distribution can form a large aperture, and the symmetrical velocity distribution presents obvious crossflow layers that are helpful for removal of rock fragments from the matrix. The numerical simulation results agree well with the actual flowing structure and the rock breakage features. A hole with expected characteristics can be drilled through adjusting nozzle structural parameters.