Erosion pattern of cavitating jet under wall constraint effect

The research on the erosion effect and erosion pattern of the cavitating jet is essential to improve the jet's guided fracturing ability. The guide port structure and the target surface impose wall constraints on the jet outlet flow and affect the jet erosion effect, but its influence law and the evolution process of erosion pattern are still not clear. The influence mechanism of the radial wall constraint formed by the diameter and length of the guide port and the flow wall constraint formed by the impinging distance on the development and collapse of jet cavitation is analyzed. Based on the erosion test, the mass loss and surface erosion morphology of the sample are obtained. The influence law of the structural size of the guide port, the impinging distance on the jet erosion effect and the evolution law of the erosion pattern are analyzed, so as to explore the erosion effect of the jet on the sandstone under different erosion patterns. The experimental results show that the added guide port structure can greatly enhance the jet erosion effect. Compared with the normal organ-pipe nozzle, the guide port-nozzle has a mass loss increase of 215%. With the increase of the impinging distance, the sample mass loss presents a characteristics of two erosion peaks, and the jet erosion achieves the strongest in the range of the second peak impinging distance (s/d=8-10). After the second peak impinging distance, the jet erosion effect decreases sharply. By reducing the guide port diameter (D_c/d=4) or increasing the guide port length (L_c/d=8), the erosion effect increases significantly, the mass loss increases by 10 times. The cavitating jet can produce different erosion patterns, with the increase of impinging distance, the doublering erosion pattern changes to single-ring erosion pattern, and the erosion morphology of the sample under single ring erosion pattern is greatly affected by the guide port structure. A sandstone erosion test was carried out. It was found that under the first peak impinging distance, the erosion pit appears as inverted funnel-shaped and the bottom surface is uniform. Under the second peak impinging distance, the depth and volume of the erosion pit are greatly improved, and there are obvious protrusions at the bottom. The research results reveal the influence law of the wall constraint formed by the guide port structure and impinging distance on the jet erosion effect and erosion pattern, which provide a technical support for improving the guided fracturing effect of water jet technology.