Naming conventions for stresses acting in flowing fluids

What is it about?

To calculate a given flow pattern of a fluid, equations have to be formulated, often from balancing forces acting on an imagined volume in the fluid, and the solutions of these equations give the flow pattern. The problem with this is that one does not know the directions in which the forces act in advance, this is part of the solution. Rules ("conventions") have, however, been set up for naming the forces and their signs so the equations can be set up without knowing the solution. More than one set of conventions exist in the literature, and this can be confusing to students of fluid dynamics. This paper explains these conventions, identifies the best one by using example flows and highlights the problems arising from trying to decide on the directions in which the forces act in order to formulate the equations "intuitively" instead of following the rules.

Featured Image

Why is it important?

Understanding and knowing the naming conventions for stresses acting in flowing fluids will allow students of fluid dynamics to read and appreciate the most known and famous texts in fluid dynamics.