ABSTRACT
This chapter presents the theory that follows aspects from the classical hydrodynamics developed by eighteenth-century scientists, who studied the motion of fluids using mathematical models that assumed that the fluid had no viscosity and was incompressible. Relations describing the flow of an inviscid fluid may frequently be used to indicate the behaviour of a real fluid away from the boundaries. The circulation round a large circuit equals the sum of the circulations round component small circuits contained within the large circuit. The vorticity at a point is the ratio of the circulation round an infinitesimal circuit to the area of that circuit. The concept of irrotational flow lies behind much of what follows and we pause to consider its physical interpretation. Flow in regions where the vorticity is other than zero is said to be rotational. In practice there may be rotational motion in one part of a flow field and irrotational motion in another part.
