Experimental investigation of passive cavitation control on a cylinder using proper orthogonal decomposition

Abstract

Cavitation is known for its hazardous effects such as material erosion, noise, vibration and drop in efficiency of hydro turbomachines. There are various approaches to control cavitation: surface roughness, cavity generator (CG), obstacles, and ventilation with air/water jetting. In the present work, we are aiming to examine the cavitation suppression by using riblets on the surface of a circular cylinder. The experiment will be carried out for two kinds of scalloped riblets, horizontal (SC-H) and vertical (SC-V), and compared without riblet cylinder (plain) at Reynolds number 1 × 10⁵. The local force is measured by using a load cell and dynamic pressure is monitored through a pressure sensor. The cavitation structures are first captured through the high-speed camera and analyzed through image processing by using Matlab. It is found that the lift force amplitude varies from 1.2 N of the plain cylinder to 0.57 and 0.48 N for the cylinder with horizontal and vertical riblets respectively. The dynamics of the cavity behind the cylinder are visible in the time-averaged mean image. The image is separated into three regions for a more in-depth examination: the far field, the center field, and the area adjacent to the cylinder. This serves to highlight certain important facts about cavity dynamics. In order to emphasize the spatial and temporal dynamics of coherent structures, the proper orthogonal decomposition (POD) is used. It is discovered that the POD modes of coherent structures can be well explained by the first five modes. Furthermore, it is found that while SC-V is capable of stabilizing the cavitation structures by limiting fragmentation, SC-H substantially controls the cavitation and chaotic behavior.