Ideal Flow around a Long Cylinder

• Published in: Fundamentals of Ship Hydrodynamics p. 1
• Main Author: Birk Lothar
• Format: Book Chapter
• Language: English
• Published: Chichester, UK John Wiley & Sons 2019; John Wiley & Sons, Ltd
• Subjects: boundary value problem; fluid flow; long cylinder; Marine Engineering & Naval Architecture; potential flow; pressure distributions; Ships & Vessels; velocity potential
• ISBN: 1118855485; 9781118855485
• DOI: 10.1002/9781119191575.ch17

As an example of potential flow, this chapter solves the basic equations that describe the fluid flow around an infinitely long cylinder oriented with its axis perpendicular to the flow. It solves the boundary value problem for the cylinder in parallel flow, and derives the velocity potential. The chapter also explains the resulting velocity and pressure distributions. It uses the pressure distribution on the cylinder surface to compute the resultant pressure force. This problem is also known as d'Alembert's paradox because, in contrast to all practical experience, the computation will find a net zero force in all directions. Of course, pressure forces do not vanish for all potential flows. The picture changes already when one considers, for example, the unsteady potential flow around a cylinder moving through the fluid at rest. Although this thematically belongs to seakeeping and maneuvering, it is shown that the resultant pressure force gives rise to the so called added mass.