当设计航海推进器时,人们力图使σ_c值最小,以便改善推进器的气穴性能使达最优。表面粗糙非常重要,因为它会使σ_c加大。因此,必须了解表面不平整的极限气穴特性,以便尽可能减弱不平整对气穴性能的不利的影响。霍尔(Holl)指出,共有三种极限气穴的可能类型,即蒸汽气穴,空气穴或伪气穴。虽然我们在下一节中也考虑到空气气穴有关的问题,但是本文讨论的主要气穴类型是蒸汽极限气穴。 When designing navigating thrusters, one seeks to minimize σ_c values ​​so as to optimize the propeller cavitation performance. Surface roughness is very important because it increases σ_c. Therefore, it is important to understand the ultimate cavitation characteristics of surface irregularities in order to minimize the adverse effects of unevenness on cavitation performance. Holl pointed out that there are three possible types of ultimate cavitation, namely vapor cavitation, air cavitation or pseudo-cavitation. Although we also consider air-pocket related issues in the next section, the main type of pocket discussed in this article is the vapor-limiting pocket.