A specialized French-language scientific text on fluid mechanics where the density of the fluid is not treated as constant. The title points to a technical treatment of variable-density flows, a topic central to stratified fluids, compressible effects, thermal convection, and environmental or industrial problems. The work is intended for readers with prior training in fluid dynamics, applied mathematics, physics, or engineering, and it likely develops the governing principles and modeling methods needed to describe flows in which mass density changes with pressure, temperature, composition, or position. With 242 pages in a paperback format and a valid ISBN, it appears to be a compact but substantial reference for advanced study, research, or professional consultation rather than a general introductory overview.