The class of hydrodynamic and aerodynamic free-surface problems with internal velocity-discontinuity surfaces is of great theoretical and practical interest.In problems of jet collisions, pneumonics, interaction of flows with different dynamic pressures, one deals with flows with internal discontinuity surfaces. In particular, the problem of internal waves in a two-layer liquid is classed among these problems.There are numerous methods for solving problems of two-dimensional flow with different Bernoulli constants both in linear [1,2] and nonlinear [3][4][5][6][7][8][9] formulations. A considerable number of publications in this line are devoted to problems of internal waves.An effective method has been proposed [10][11][12] for precise nonlinear calculations of plane and axisymmetric flows of an ideal fluid with free surfaces. The present paper extends this method to the case of flow with discontinuity surfaces of the Bernoulli constant.The method is described and tested by calculation of the problem of potential two-layer flow above a curvilinear bottom in the class of soliton-type solutions. The particular case of this problem with a rectilinear. bottom has been studied by a number of authors.The proposed method allows one to obtain a numerical solution of the problem for a curvilinear bottom of an arbitrary shape, while the most effective method of calculating such flows [9] is applicable only for the particular case of a bottom irregularity in the shape of a circular half-cylinder.The accuracy of the method is tested by comparison of numerical and exact solutions of a certain model problem.Let us consider a two-dimensional problem of steady two-layer potential flow of a heavy fluid over an obstruction located on a horizontal straight bottom. The parameters for the lower layer are denoted by subscript 1, and those for the upper layer, by subscript 2. The flow dia3ram is shown in Fig. Soliton-type solutions symmetric about the vertical axis x = xo/2 (xo is the length of the obstruction) are sought for the free-surface and interface shapes.Let V + and V 1-denote the flow velocity along the inner interface with approach to this interface from above and from below, respectively.The condition of pressure continuity for passage through the interface, according to the Bernoulli equation, leads to the following relation for velocities on the sides of the interface:Here Pl and P2 are the fluid densities, Frl = Vool/vf~ is Froude's number for the lower layer, g is the acceleration of gravity, and H1 is the interface ordinate at infinity. The constant-pressure condition along the free surface is equivalent to the following law of velocity distribution along it:V~ 2 =l-Fr--~2 H2-1 ,