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 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 energy interactions is performed on a graphics processing unit (GPU), wherein minimizing the sum over the energy interactions comprises minimizing E=√{square root over (Σ ij E ij 2 )} wherein E ij = { W n ×  t ij - e ij  , e ij < d , W nn ×  t ij - g ij  , g ij > d , wherein w n and w nn are weights for neighboring and non-neighboring blocks, respectively, t ij =|v i −v j | is a target distance between blocks b i and b j in a 2D image wherein v i and v j are 2D positions of b i and b j , e ij is a Euclidean distance between b i and b j in the 3D volume, g ij is a geodesic distance between b i and b j in the vessels in the 3D image, and d is a threshold that separates neighboring blocks from non-neighboring blocks, wherein the minimization is performed by varying the target positions v i and v j ; and using the minimized energy E 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.