Natural convection in a narrow horizontal cylindrical annulus: Pr ≤ 0.3

Abstract Natural convection in a narrow horizontal cylindrical annulus is numerically investigated for fluids of Pr ≤ 0.3. For Pr ≤ 0.2, hydrodynamic instability induces steady or oscillatory flows consisting of multiple like-rotating cells. For Pr = 0.3, thermal instability creates a counter-rotating cell on the top of annulus. For a fluid of Pr ≈ 0, the multiple cells are distributed uniformly in the lower and upper parts of annulus. As Pr is increased, the cells are shifted upwards. The like-rotating cells drift downward, as time goes on, and the speed of travel increases with increase of Pr. For Pr = 0.3, the oscillatory flows after secondary instability consist of multiple like-rotating cells in the vertical section of annulus and one or more counter-rotating cells on the top part, and multiple oscillatory flows are found.