Le flux d'énergie en mécanique: Application aux turbo-machines
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The concept of flux of energy, first introduced in electrodynamics byJ. H. Poynting, can be extended to the domain of fluid-mechanics. It conduces to recognize in the flux of energy for a continuous portion of matter two parts: the first one, which can be called ‘transported’, corresponds to the energy localized in the matter and carried with it as a consequence of its displacement; the other results from the work developed by the stresses and can be called ‘transmitted’.
The expression of this flux of energy in the general case of variable motion of a compressible fluid introduces the concept of enthalpy. Its application to an extension ofHelmholtz's theorem on the conservation of vorticity in a perfect fluid, according which bound vortexes have a definite relative motion across the fluid, contributes to explain the mechanism by which, even in the case of grids with a large pitch: chord ratio (Kaplan turbines, screw propellers), the energy of all parts of fluid is finally transmitted to the moving blades.
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