1. A method for visualizing flow data from computation fluid dynamics (CFD) applications in 2-dimensions (2D), comprising the steps of: receiving a 3-dimensional (3D) image volume from a CFD simulation of fluids flowing through vessels in a patient that is a snapshot of a fluid flow in the vessels at a certain time; subdividing the 3D image volume into 3D data blocks; minimizing a sum over a matrix of energy interactions defined for each pair of data blocks in the 3D image volume, wherein said minimization preserves a local shape of the vessels, wherein minimizing the sum over the matrix of energy interactions is performed on a graphics processing unit (GPU); and using the minimized energy interaction matrix to display on a monitor a 2D sketch of the 3D image volume, wherein the 2D sketch is displayed in real-time with respect to the time scale of the CFD simulation.