磁致伸缩仪超声空化流的三维非定常数值模拟

3D Unsteady Numerical Simulation of Magnetostriction-induced Ultrasonic Cavitation Flow

采用Singhal完全空化模型和SSTk-ω湍流模型结合动网格技术对磁致伸缩仪超声空化流进行三维非定常数值模拟。计算结果表明,由于变幅杆高频振动,在靠近试样表面附近局部流场的压力和空泡体积组分变化具有周期性,压力波动的最低值可达到汽化压力,该局部流场可发生空化。由于空化,试样表面压力波动具有脉冲特征。压力和空泡体积组分在试样表面近似呈环形分布。在同一环形区域内,压力和空泡体积组分存在无规律断续脉动。试样表面中心区域空泡经历两次振荡后溃灭,产生强烈脉冲压力,最大脉冲压力可达约14MPa。脉冲压力在试样表面按间隔环形区域分布,且随试样振动在相邻环形区域上交替出现。在磁致伸缩仪超声空化流场中,试件表面可近似多个声波发生源,各声波传播时相互叠加和干扰。在声波传播的过程中压力衰减很快,只是在距试样表面约20mm内,压力有明显波动。

The magnetostriction-induced ultrasonic cavitation flow was numerically simulated by using a＂Singhal full cavitation model＂and SSTk-ωturbulence model with the dynamic mesh technique.The characteristics of ultrasonic cavitation flow and the cavitation erosion mechanism were revealed.The computational results show that pressure and vapor volume fraction（VVF）vary periodically on the specimen with vibration of the specimen.The lowest value of pressure fluctuation reaches the vapor pressure at the local flow field proximity to the specimen,where cavitation can occur.Pressure fluctuation presents a distinct pulse feature on the specimen surface,due to cavitation.Moreover,pressure and VVF were annularly distributed around the center on the specimen.However,they have irregular and discontinuous pulse in the annular zones.At the center of specimen,bubbles collapse leads to intense pulse pressure after twice oscillation,which can reach about 14 MPa.Pulse pressure was distributed in the interval annular zones and alternately occurs in the adjacent annular zones with vibration of the specimen.In the ultrasonic cavitation flow field,the specimen surface seems to be as several acoustic emission sources.The acoustic waves generate mutual superposition and interference.Pressure dramatically attenuates with increasing the distance to the specimen.The considerable pressure fluctuation occurs within the distance of about 20 mm to the specimen.