Exnerimental Studies On The Bubble Dvnamics Generated By Underwater Discharge

Bubbles are the multi-phase phenomenon and widely applied in various fields,such as seismic exploration,shipbuilding and chemical engineering,etc.In the field of seismic exploration,the seismic sources mainly include air-gun and sparker,the acoustic radiations are induced by the bubble oscillations,which have obvious influence on the source level and frequency band of the acoustic signals.At present,the plasma sparker has been widely applied in the high-resolution seismic exploration,where the acoustic radiations are generated at the multi-electrode array,and the plasma-containing bubbles are induced at the electrode tips.In this paper,a 30-J pulsed source was used to generate single or multi-bubble under different discharge polarities and electrode parameters,a voltage probe and a current sensor were used to measure the load electrical parameters,and the high-speed camera was used to record the bubble oscillations.The main contents and conclusions are summarized as follow:(1)The load electrical characteristics are studied.The results show that positive discharge has a residual voltage at the end of pulsed discharge.Moreover,the load voltage and energy decrease with increasing electrode numbers.whereas the load current and power increase when electrode numbers increase.In addition,when the charging voltage ranges from 2.22 kV to 4.72 kV,the load electrical parameters change little at the electrode distance larger than 25 mm;(2)The bubble dynamics are investigated.It is found that a single bubble generated by positive discharge has a larger size than that generated by negative discharge at the same discharge energy.In terms of the 2-electrode discharge at 4.72 kV,the bubble energy efficiency is 10.5%for bipolar discharge,whereas are 6.3%and 5.1%for positive and negative discharge.In addition,the bubble energy efficiency decreases with increasing charging voltage.The experimental results also indicate that the bubble interactions are negligible when the dimensionless electrode distance larger than 1.3.The bubble energy efficiency decreases with increasing electrode numbers;(3)The load electrical characteristics and single-bubble dynamics are simulated.The simulation results show that the load impedance decreases with increasing charging voltage.The vapor pressure inside the bubble has been fitted by the experimentally measured maximum radius and period,and the Rayleigh-Plesset model has been corrected.the fitting results show that the bubble induced by negative discharge has a 21 kPa vapor pressure.whereas it is 15 kPa for III positive discharge.The simulation results are in good accordance with the experimental ones.