DNS and LES of Turbulent Natural Convection Boundary Layer

• Turbulent natural convection boundary layers possess some special characteristicscompared to the other boundary layers.In order to study this kind of boundary layer, two powerful numerical methods,Direct Numerical Simulation or DNS and Large Eddy Simulation or LES,are used. The former is used to investigate the natural convection boundary layer in avertical channel for which the Grashof number based on the channel width isGr_h=9.6*10^5 and the latter is used to study the natural convection ina cylindrical vertical shell and tube. The local Grashof number in the lattercase reaches Gr_z=5*10^11. Mean flow parameters as well as turbulenceparameters in the both cases are studied and the results are compared with theexisting experimental results for natural convection boundary layer on a flatplate and natural convection boundary layer on a vertical slender cylinder.Although many qualitative and quantitative agreements are found between the results,there are still some discrepancies in the turbulence characteristics.A region with negative shear stress in the boundary layeralong the vertical cylinder, which is in agreement with many experimentsis observed and the effect of it on the boundarylayer is studied. However, there is no such region in the boundary layer inside thevertical channel. Also the existence of a linear region for the velocity profilewhich is much thinner than the ordinary forced convection boundary layers isconfirmed.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Keyword

DNS

free convection

LES

natural convection boundary layer

vertical cylinder

Publication and Content Type

lic (subject category)

vet (subject category)