Pisarenko Institute of Problems of Strength, National Academy of Sciences, Ukraine

Biography: Dr. Alexander Khotsianovsky is currently a senior research fellow at the Institute of Problems of Strength (IPS), Kiev, Ukraine. After receiving the Ph.D. degree in Mechanical Engineering and Fracture Mechanics at the National Academy of Sciences of Ukraine in 1990, he conducted research in the field of innovative spacecraft and aircraft applications in IPS, Ukraine, as an invited research fellow in German Aerospace Research Establishment (DLR, Cologne,Germany,1993-1995), and Computer Control Solutions (CCS, Dublin, Ireland, 2001-2002). In 1996-2000, he was hired by USAID as a full-time technical consultant to six technical assistance projects financed by the USAID with the total budget of 5 mln USD in four CIS countries, including Ukraine (Kiev and ten more pilot cities), Russia (Irkutsk), Moldova (Cisinau) and Kazakhstan (Alma-Aty). His current research interests cover a wide range: from coatings, tribology, and fretting-fatigue of advanced space/aircraft materials to polymer-additive applications and numerical simulation of hydroelasticity problems for supercavitation high-speed underwater vehicles. He takes an active part in the advanced material development for spacecraft applications in Ukraine (IPS, Kiev) and ONR/DARPA international projects on drag reduction of superspeed underwater vehicles.

Speech Title: Underwater high-speed motion stabilization by supercavitation, aqueous polymeric, and super-hydrophobic surfaces: experimental and theoretical design solutions

Abstract: The high-speed motion of underwater vehicles, including ultrasonic supercavitation torpedoes such as Shkval (Russia) and Barracuda (Germany), is more unstable than a tightrope dancing: any changes in the motion direction or velocity will break the equilibrium unless special measures are immediately taken. The latter include such alternatives as (i) online control of the envelope supercavity dimensions by a movable cavitator and gas pressurization; (ii) motion stabilization by periodic injection of aqueous polymeric solutions into turbulent shear flow, and (iii) drag reduction by the wetted area optimization via super-hydrophobic fin/tail surfaces. This study presents some new experimental results on drag minimization and motion stability improvement for supercavitation torpedo models in Ukraine by adding aqueous solutions of high-molecular linear-chain polymers, which form a “liquid membrane” around the moving underwater vehicle, as well as by producing an ellipsoidal supercavity inflated by natural airflow, which "opens an umbrella" over its major part. The results obtained are validated by numerical simulation and similar findings of US and China research teams. The third alternative concerning super-hydrophobic or super-hygrofobic surfaces has been introduced in Israel by the second co-author based on fundamental theoretical studies of thermodynamic equilibrium and stability equations of the Wenzel and Cassie-Baxter wetting states. Thus, the energy barriers for the liquid drop motion on a surface have to be minimized, while the required surface roughness geometry (including a multi-scale one) has to conform to a particular mathematical condition (e.g., convex protrusions enable it, in contrast to concave dents). Based on the above theoretical guidance and available empirical results, a steering fin/pylon with the optimized ratio of supercavitation and wetted areas was numerically tested and experimentally validated in the experimental basin with a scaled-down model within framework of the ONR Project (US) in Ukraine. The advantages and limitations of the above approaches and their comprehensive integration are summarized.

Keywords: underwater high-speed motion, supercavitation, polymeric solutions, wetted area, superhydrophobic surface