New classes of exact solutions of the three-dimensional unsteady Navier-Stokes equations containing arbitrary functions and parameters are described. Various periodic and other solutions, which are expressed through elementary functions are obtained. The general physical interpretation and classification of solutions is given.Keywords: Navier-Stokes equations, exact solutions, periodic solutions, three-dimensional equations, unsteady equations.
Class of motions of the viscous incompressible fluid under considerationSelf-similar, invariant, partially invariant, and certain other exact solutions of the Navier-Stokes equations including those with generalized separation o f variables were considered, for example, in [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Below, the term "exact solutions" is used according to the definition given in [14, p. 10].Three-dimensional unsteady motions of a viscous incompressible fluid are described by the Navier-Stokes and continuity equations: