Fekhar, MustafaSaci, Rachid(Directeue de thèse)2022-03-222022-03-222022https://dspace.univ-boumerdes.dz/handle/123456789/772085 p. : ill. ; 30 cmThermal buoyancy, induced by injection or by differential heating of a rod, is explored to control breakdown onset which occurs in the core of a helical flow driven by the lid rotation of a vertical cylinder. Three main parameters are required to characterize numerically the flow behavior; namely, the rotational Reynolds number Re , the cavity aspect ratio ? and the Richardson number Ri . Warm injection/rod, 0 Ri ? , is shown to prevent on-axis flow stagnation while breakdown enhancement is evidenced when 0Ri ? . In addition, when 0 Ri ? , results revealed that a bubble vortex evolves into a ring type structure which may remain robust, as observed in prior related experiments or, in contrast, disappear over a given range of parameters ( 0 ) ,, i R e R ?? . Besides, the emergence of such a toroidal mode was not found to occur under thermal stratification induced by a differentially heated rod. Moreover, three state diagrams were established which provided detailed flow characteristics under the distinct and combined effects of buoyancy strength, viscous effects and cavity aspect ratioenBreakdownCylinderBuoyancyInjectionThesis