Mitigation of Hydrodynamic Resistance

The following sections are included:

• Dedication
• Preface
• Acknowledgments
• Contents

All types of vehicles encounter resistance to their (forward) motion, and minimizing this resistance has been a goal of engineers and designers for time immemorial. Hydrodynamic resistance, for example, of surface and sub-surface vehicles can broadly be separated into the following physical processes: (1) skin friction drag, (2) form drag, (3)wave-making resistance, and (4) induced drag. Designers strive to minimize the total resistance of a vessel while maintaining desired operational characteristics. However, the minimization of one form of resistance often leads to an increase in another. For example, the use of long and slender hulls can reduce both form and wave drag but may lead to an increase in skin friction drag…

The following sections are included:

• Background Information
  • Inner variables and scaling
  • Background for PDR
• Internal Flows at High Re
• External Flows and PDR
  • The experiments of Winkel et at. (2009)
  • K-factor scaling of PDR
  • The effects of roughness on FDR in a TBL — the experiments of Elbing et al. (2011)
  • Another study on surface roughness effects but conducted at smaller Re
• Polymer Release with Coatings
• References

As there has been a recent Annual Review of Fluid Mechanics review of this topic by one of the authors (Ceccio, 2010), the interested reader is referred there. Much of that publication discusses cavities and air layers for underwater and surface vehicles — these discussions followlater in this text. To begin our discussion, we mention the first paper that discusses successful drag reduction by bubble injection, McCormick and Bhattacharyya (1973). For a review of bubble drag reduction (BDR) through 1992, the reader is directed to a review by two Pennsylvania State University faculty, Merkle and Deutsch (1992). Here, we reproduce an introductory paragraph from the paper Sanders et al. (2006) that provides some general background…

First, we discuss the transition from bubble drag reducing flows, where there are discrete small bubbles interacting with the underlying liquid turbulent boundary layer, to the formation of air layers, where bubbles have merged to form a high void fraction region between the outer flow and the solid surface. We then evaluate the implementation of air layer drag reduction (ALDR).

To begin our discussion of PCDR, Makiharju et al. (2010) (Inter. Conf. Multiphase Flows) is reviewed. The experimental setup included the HIPLATE, but with significant structural changes (over the one discussed so far) that facilitated the cavity (i.e. a backward-facing step (BFS) was added as well as a cavity-closing “beach”). In addition, the instrument suite was altered to include three laser Doppler velocimeters (LDVs) in addition to the upstream reference LDV, and three traverses that protruded into the flow and were perpendicular to the plate’s working surface. The traverses included a set of sensor packages.

This chapter is concerned primarily with super and partial cavities on axisymmetric bodies. In addition, as discussed previously, we present material on two-dimensional partial cavities on bodies with nominally horizontal surfaces. As one of the authors (SC) recently published a paper on this subject, we follow closely that presentation (Ceccio, 2010). Axisymmetric cavity flows with gas injection are not discussed in detail herein; as excellent reviews are available (Knapp et al., 1970; Wu, 1972; May, 1975; Brennan, 1995) we discuss them only briefly…

Since Onda et al. (1996) demonstrated the properties of super-hydrophobic surfaces (SHS), there has been a considerable amount of research into the physics and applications of these surfaces. These surfaces have novel properties that have been exploited to repel liquids from them (including cloth surfaces, for example). Our discussion here will focus on the potential use of SHS to reduce drag developed by flowing liquids…

In this chapter, we discuss appendages that serve to reduce the overall friction drag of an object moving in or on the surface of a liquid at high Reynolds number, such as ships and submarines. These appendages include bulbous bows, stern flaps, stern wedges, stern bulbs, lifting bodies, interceptors, and the like are application-driven and hence specific to a given hullform. Hence arriving at relevant canonical experiments are difficult. Yet, all these appendages are added to reduce propulsor demand or equivalently to increase speed, albeit in different ways…

The following section is included:

• Index