掺气减蚀保护作用的新概念

New concept of air entrainment effect on mitigating cavitation damage

利用针式掺气流速仪测量原型和模型掺气浓度场、流速场,气泡尺寸及其概率分布的研究成果表明,原型水流韦伯数高,形成微小气泡的能力比模型强,气泡上浮慢,接近底部的小尺寸气泡概率及掺气浓度比模型大。初步研究认为:0 2mm或0 5mm以下的微小气泡在掺气减蚀中起着主要作用,可能只要很小掺气浓度即可达到掺气减蚀的效果。因此以小尺寸气泡的掺气浓度,作为判断掺气减蚀保护作用的指标将更为准确。

Concentration distribution, velocity field, probability distribution of bubble dimension and absolute dimension of bubble are studied by using needletype air concentration probes both in model and prototype. It is found that the capability of air entrainment forming small bubble in prototype is higher than in model due to higher Weber number. Thus, the process of bubble buoying up is slower in prototype. The probability of small bubble and concentration of air entrainment near the channel bed is higher in prototype. The bubbles with diameters below the 02mm or 05mm play important role in mitigating the cavitation erosion. Accordingly, it is reasonable to adopt the concentration formed by small bubble as the criterion for appraising the air entrainment effect on mitigating cavitation damage.