The Experimental Study And Numerical Simulation Of Jet Feature By Central-body Nozzle

Cavitation in jet flow is a new water jet technology, which has been sucessfully applied to the coal mining, oil drilling, cutting, cleaning and other industrial areas. And now there are three different nozzles that can generate the water jet include the cavitation, and these are organ pipe nozzle, triangular nozzle and the central-body nozzle. The foreign and domestic scholars have launched a series of experimental studies and numerical simulation of the organ pipe nozzle and triangular nozzle, while the central-body nozzle is studied less.Research works in this paper were supported by the national natural science foundation "the mechanism of cavitation effected by the scal of vacuole in the process of the cavitation water jet (50806031)". The free water jet generated by the central-body nozzle was measured by PDPA and calculated to analyse the energy feature; the cavitation jet under water was captured by the high-speed digital camera and the cavitation field was analyzed to analyse the cavitation feature; the corresponding experiment of the erosion was carried out, the ability of attack of the cavitation water jet was studied to determine the best target distance, and finally to improve the coupled theory of liquid and solid.The main content of this research concludes as follows:1. Under the different inlet pressure, the free water jet generated by the central-body nozzle was measured by PDPA to gain the velocity, droplet size and fluctuation velocity, meanwhile using the VOF model, the gas-liquid field in the free jet was calculated by Fluent.The result of experiment and simulation is that, the axial velocity in the core area decays very slowly, under the inlet pressure of 15MPa, 105mm away from the nozzle outlet, the average axial velocity reduces by 0.7%, while the radial velocity increases as the spread of the jet beam; in the jet process, as large volume of air is wrapped in, the jet beam becomes the gas-liquid mixing jet, near the boundary of the core area there are mainly droplets, the turbulent kinetic energy and fluctuation are bigger than those in the core area, and the jet energy exchanges greatly, the the turbulent kinetic energy and fluctuation velocity were the basis to measure the diffusion and the exchange of energy; the energy in core area is assembled, and the droplet size is bigger than those in the shear layer; when the inlet pressure is bigger, the jet velocity is bigger, but the droplet size change little.2. The water jet generated by central-body nozzle under the water was shot by high-speed digital camera, and the cavitation field generated by the different inlet pressure was calculated. The result shows that the axial velocity of the water jet under the water is increasing while the inlet pressure is bigger, but decays rapidly; the cavitation area includes three areas and these are the straight pipe of the nozzle, the back of the central-body and the cavitation tongue circumference, big turbulence kinetic energy and fluctuation velocity exited behind the central-body, this place could generate cavitation, which was the main area where the cavitation emerged and also the vacuole assembled; the boundary of core area under water is consisted by air bubbles, while the core area is consisted by liquid, air bubbles and cavitation bubbles; the volume fraction of vacuole in the water jet was increasing and diffused greatly when the inlet pressure was bigger.3. The corresponding experiment of the erosion was carried out between the central-body nozzle and normal nozzle. The result shows that the erosive effect is better, when the inlet pressure was bigger, the time was longer and the range was smaller; when the inlet pressure is from 13MPa to 22MPa and the range is within 20mm, the erosive effect of central-body nozzle is better than the normal nozzle, while the range is beyond 30mm, the erosive effect of normal nozzle is better; the range and the erosive effect were decided by the length of the cavitation bubble, while contrasting the normal water jet, the cavitation water jet had the best range, under the inlet pressure is from 13MPa to 22MPa, the best range is from 7mm to 17mm.