In 1752 Euler wrote a first paper in Latin Principia motus fluidorum (Principles of the motions of fluids) which presented the equations of incompressible fluid dynamics in slightly cryptic notation (choice of units and use of differential forms). This work was presented to the Royal Academy of Prussia in Berlin on August 31, 1752. It had however a significant mistake, previously made by d'Alembert: the vorticity was taken to vanish.
Rather quickly Euler must have realized that vortical solutions are important. On September 9 and october 2, 1755 he presented to the same academy Principes généraux du mouvement des fluides (translation: General laws of the motion of fluids) of which the only hand-written copy (not by Euler) is preserved at the archives of the French Academy of Sciences. The paper was published in 1757 in the proceedings of the Berlin Academy. The paper in Latin was eventually published in St. Petersburg in 1761.
In the introduction of volume 12 of the Opera Omnia of Euler, Clifford Truesdell presented the Latin paper and the French paper in detail. The recent book on the history of fluid dynamics Worlds of flow by Olivier Darrigol (Oxford University Press 2005) discusses Euler's work on fluid dynamics in the context of 18th century research.
For all the papers of Euler and extensive background and historical discussion, see the Euler Archive.