Jh. Arakeri et al., Convection in a long vertical tube due to unstable stratification - A new type of turbulent flow?, CURRENT SCI, 79(6), 2000, pp. 859-866
We present experimental results of free convection in a vertical tube due t
o an unstable density difference imposed between the two (open) ends of the
tube. Two tanks of fluids connect the two ends of the tube with the top-ta
nk fluid heavier than the bottom-tank fluid. We use salt mixed with water t
o create the density difference. The convection in the tube is in the form
of relatively heavier fluid going down and lighter fluid going up simultane
ously; the mean flow at any cross section of the tube is zero. Depending on
the Rayleigh number we observe different types of flow, with turbulent flo
w being observed at the higher Rayleigh numbers. We believe this is a new t
ype of turbulent flow-a nearly homogeneous, buoyancy-driven flow with zero
mean shear.