Viscous Drag Reduction In Boundary Layers

While other methods of drag reduction are well-known in marine R&D and ship design environments worldwide, compliant coating drag reduction remains less well-known and poorly understood. This important book presents cutting-edge techniques and findings from research sources not generally accessible by Western researchers and engineers, aiding the application and further development of this potentially important technology. Beginning with an introduction to drag reduction that places the authors’ work on elastic surfaces and combined techniques in context, the book moves on to provide a comprehensive study of drag reduction through elastic coating with both flow and material properties considered. Coverage includes: Experimental findings around coherent vortical structures (CVS) in turbulent boundary layers and methods of controlling them Static and dynamic mechanical characteristics of elastic composite coatings, as well as new techniques and devices developed for their measurement Combined methods of flow control and drag reduction, including the effect of injection of polymer solutions, elastic coatings and generated longitudinal vortical structures on hydrodynamic resistance Intended as a reference for senior engineers and researchers concerned with the drag reduction and the dynamics of turbulent boundary layer flows, Boundary Layer Flow over Elastic Surfaces provides a unique source of information on compliant surface drag reduction and the experimental techniques around it that have shown measurable and repeatable improvements over recent years. This compilation of research findings and new techniques developed for measurement will aid R&D engineers, naval architects and senior designers in their quest to achieve drag reductions that will deliver significant efficiency savings. Unique source of information on compliant surface drag reduction—an important area of technology with practical application to ships—from otherwise inaccessible research studies Updates the knowledge-base on boundary layer flow and surface friction reduction, critical topics in the global quest for increased ship efficiency and fuel economy Reveals new techniques and devices developed for measurement and provides a comprehensive study of drag reduction through elastic coating with both flow and material properties covered

The phenomenon of resistance to motion through a fluid is believed to be a function of fluid-wall interaction. This theory is based on the assumption that under certain conditions a real fluid does not usually slip on the wall in contact with it and displays laminar flow. This set of conditions is known as a ‘no slip boundary condition’. But if a fluid is passed alongside a wall, the drag reduction in the laminar flow region can be calculated. In Laminar Drag Reduction, the frictional drag of an internal or an external fluid flow along a certain kind of hydrophobic wall is investigated. An analytic approach towards the mechanism of drag reduction is employed using Navier-Stokes existence and smoothness equations. The experimental results presented in this book show that frictional drag of a fluid alongside this hydrophobic wall decreases in comparison with fluid flow along a conventional wall or surface. This form of laminar drag reduction represents a relatively new area of research, where the laminar flow can be controlled by microscopic surface modifications, allowing fluid flows to slip over a wall. Laminar Drag Reduction brings information about some interesting phenomena related to fluid slippage on a highly water-repellent surface. Readers, physics graduates and senior researchers alike, can benefit from the information presented in this book to tackle more challenging questions in fluid mechanics research.

In this study two important topics have been investigated. First, a new automation procedure has been developed to detect fringe patterns in oil- film interferograms. The procedure combines a windowed Fourier transform and a cross correlation technique to determine regions where fringes are likely to reside. The cross correlation of a single cycle cosine function and the original intensity produce a filtered result that isolates the information being sought. The automation procedure is able to capture approximately 75% of the fringes in an image but additional refining of the technique could increase this percentage. Second, the effect of viscous fore-body drag on base drag has been investigated on a 2-D ramp model. Measurements made during the study include oil-film interferometry and hot-wire anemometry for viscous fore-body drag, and pressure measurements on the fore-body and base for fore-body and base drag. The results of this investigation show that an increase in viscous fore-body drag has very little effect on base drag, which contrasts previous studies where increases in viscous fore-body drag tended to decrease base drag. This means that a simple jet pumping mechanism is not the sole effect responsible for base drag reduction in this type of geometry. Hot-wire measurements in the wake of the model show that the flow in the base region is devoid of a dominant shedding frequency. It may be possible that the boundary layer somehow affects the vortex shedding mechanism but further investigations would be necessary to demonstrate that this is true.