87 / 2023-06-14 15:04:46

Modulation mechanism of self-excited oscillation pulsed submerged waterjet enhanced by annular fluid

submerged waterjet,large eddy simulation,self-priming,response surface method,waterjet pulsating pressure test experiment

In order to improve the effect of coal breaking and permeability increasing by submerged waterjet in downward boreholes of coal mine, it is proposed to open a self-priming hole on the wall of the Helmholtz self-excited oscillation cavity, and the hydraulic energy of the annular fluid in the downward boreholes is used as an external excitation source to form an enhanced self-excited pulsed particle waterjet to enhance the submerged jet effect. Firstly, the flow field characteristics of self-excited oscillation pulsed waterjet (SOPW) and annular fluid enhanced self-excited oscillation pulsed waterjet (AFESOPW) were compared and analyzed by large eddy simulation (LES), and the enhancement mechanism of self-priming on pulsed waterjet was revealed. Secondly, the single factor experiment and the response surface method (RSM) were used to study the influence of the following five parameters on the outlet axial pulsation amplitude and the entrainment flow rate of the self-priming hole, which were the diameter of the lower nozzle d₂, the length of the oscillating cavity L, the diameter of the self-priming hole d₃ and the position of the self-priming hole h. Furthermore, the optimal modulator structure was obtained. Finally, the accuracy of the simulation was verified by the self-developed waterjet pulsating pressure test device, and the submerged waterjet performance was studied under the conditions of inlet pressure of 2~12 MPa, ambient pressure of 0~0.3 MPa and target distance of 0~5 times d₂. The simulation results show that the appropriate structure can significantly improve the self-priming effect and increase the pulsation amplitude and entrainment flow rate. The influence of the four structural parameters on the pulsation amplitude is in the order of L > d₂ > h > d₃, and the influence on the entrainment flow rate is in the order of h > d₂ > L > d₃, meanwhile there is a significant interaction between them. Compared with the jet before optimization, the outlet pulsation amplitude and entrainment flow rate after optimization are increased by 30.79 % and 29.41 %, respectively. The experimental results show that compared with the waterjet before optimization, the SOPW and the continuous waterjet, the pulsation amplitude increased by 32.56 %, 45.17 % and 330.05%, and the pulsating pressure peak increased by 25.81 %, 19.60 % and 42.84 %. The pulsation amplitude and the peak value of the pulsating pressure increase with the increase of the of the inlet pressure, and decrease with the increase of the target distance. The peak pulsating pressure at the outlet is 1.32~1.58 times the inlet pressure, and is 90 % of the inlet pressure at the target distance of 4d₂. The increase of ambient pressure will increase the pressure of the liquid column outside the self-priming hole, thus enhancing the waterjet pulsation effect and weakening the hindering effect of submerged environmental pressure on the waterjet development. In the later stage, coal and rock debris particles can be suck-in through the self-priming hole to form a post-mixed abrasive waterjet, which can enhance the effect of coal breaking and permeability increasing in the downward boreholes.