We address the problem of fluid motion estimation in image sequences. For such motions, standard optical flow methods, based on intensity conservation and spatial coherence of motion field, are not suitable. This is due to the highly deformable nature of a fluid medium. For all applications where fluid motions are to be recovered from images, it is then important to have specific techniques. We investigate such dedicated models which include an original observation constraint, based on the continuity equation from fluid mechanics, and a new div-curl-type smoothness term. Our method is validated on synthetic and real meteorological images.