This is an exploratory research project aimed at capitalizing on recent research experience with unsteady partially cavitating flows. This work has identified the significant and unexpected effect of surface properties and water quality on the dynamics of these flows. Previously it was thought that surface properties and water quality only affected cavitation inception physics. At the same time there has been significant interest in the use of hydrophobic surfaces for drag reduction. Hybrid drag reduction drag reduction schemes involving a combination of microbubble injection coupled with the use of hydrophobic surfaces have also been proposed. The PIs will explore the possibility of using hydrophobic surfaces to control or minimize unwanted vibration and unstable operation in the partially cavitating regime. Before embarking on a significant research program that would involve the development of structured hydrophobic surfaces a limited exploratory effort will identify the potential for further development of this concept. Three surfaces will be evaluated, such as anodized aluminum (hydrophilic), Teflon (hydrophobic), and highly polished stainless steel (hydrophobic). Contact angle will be measured and based on the range of contact angle that is feasible, the PIs will predict the change in cavity length and estimate the change in lift dynamics on the basis of their previous experiments and with the help of their numerical model. They will then design and build three hydrofoils of identical cross section. The first will have a hydrophilic surface; the second hydrophobic and the third will have a hydrophobic surface for one half of the span and a hydrophilic surface for the other half of the span. Comparative measurements of unsteady lift will be made. High-speed video will be analyzed to determine fully wetted time. This research has important technological broader impacts. Operation into a regime of partial cavitation has been considered for hydrofoils and is becoming common in a wide range of turbomachinery applications. This opens up a wide range of new considerations including the possibility of control of these flows to eliminate or minimize unwanted vibration and unstable operation. The results of this will research will indicate whether the use of hydrophobic surfaces for control of cavitation induced vibration and unsteadiness is feasible.
