Cavitation is a phenomenon in which bubbles (also calledcavities) are formed in specific locations in a liquid where pressure reducesbelow the vapour pressure of the liquid. Hydrodynamic cavitation is one inwhich cavities are formed either due to the relative motion between a solid andliquid or flow inside a concentric passage like venturi. In the present work, acircular cylinder in cross-flow is chosen for studying cavitation phenomenon.


Many studies are available for flow past circularcylinders, but only a very few work is available on effect blockage on flowbehind the cylinder and more so for cavitating condition. The objective of ourstudy is to investigate the blockage effect on cavitation in the wake of acircular cylinder. Based on literature review, we chose 6 blockage ratios ¾ 4%, 6%, 8%, 12%, 16% and 20% to study the effect ofblockage on cavitation.


Cavitation experiments were carried out in low speed closedwater tunnel and the pressure inside test facility was controlled by a vacuumpump. The experiments were carried out from non-cavitating flow to fullydeveloped cavitation by change of test section pressure while test sectionfreestream velocity is held constant. The methodology of our experimentsincludes high speed imaging, measurement of instantaneous and average pressureon cylinder surface and along the wall of the test section. Image processingwas carried out using Matlab to bring out the dynamics of cavities underdifferent conditions.


Cavitation inception is one of the key parameters to studycavitation. The inception point was observed for all cylinders very carefullywith high speed camera and also verified with the sound level meter (SLM) forfew cases. The SLM results are shows a decrease in sound intensity for lowerblockage and cavitation number for peak of sound intensity increases for lowerblockage. High-speed imaging shows that inception occurred in shear layer andthe cavity grows in wake as the cavitation number decreases and then there isan appearance of attached cavity at certain low cavitation number. The lengthand size of attached cavity increase with a further decrease in cavitationnumber. Static pressure measurement on the cylinder surface shows that dragcoefficient, even at non-cavitating condition, is higher for cylinders whichoffer a higher blockage. The fluctuating pressures also display the importanceof blockage. The present results suggest that, while extrapolating water tunneltest data, one needs to consider the effect of blockage. This work helps indeveloping a better understanding of the effect of blockage for cavitating flowbehind a circular cylinder in subcritical flow regime.