Abstract
Passive methods of flow and cavitation control appear to offer some of the best prospects in the field of hydraulic engineering and marine applications. In this article, we aimed at an experimental examination of the effect of wall roughness/wettability on the occurrence of cavitation and turbulence structure in the cross flow around and in the wake of a circular cylinder in two characteristic regimes. For this, we used three test bodies with different surface morphologies: smooth (reference), micro-scale irregularities (rough) and regular large-scale (of the order of a millimeter) texture (finned). Using high-speed imaging to observe vapor cavities, we revealed that cavitation is noticeably suppressed by both types of roughness. Applying the method of vapor phase detection (Pervunin et al., 2021), this finding was then quantitatively confirmed through an in-depth analysis of an ensemble of instantaneous velocity fields measured by PIV, indicating that modification of wall morphology is an effective method of cavitation control. The procedure of statistical vector filtration (Heinz et al., 2004) allowed us to remove outliers from the velocity fields and, thus, calculate various turbulence characteristics, including higher-order moments (i.e., the coefficients of skewness and excess). Wall irregularities were found to significantly affect the turbulence structure of the wake flow, but the higher-order moments downstream of the modified-surface cylinders turned out to be unexpectedly insensitive to a change in the flow regime, as opposed to the smooth one. Regardless of the type of surface morphology, the influence of roughness on the mechanism of formation of large-scale vortices and their characteristics was weakened. However, it caused overall disorganization of liquid motion in the cylinder wake, thus making local flow conditions highly unsteady. In addition, this process became more chaotic with an increase in the scale of irregularities.