Vol.4, No 1, 2006pp. 1 - 16
UDC 532.13 532.551
THREE-DIMENSIONAL STUDY OF VORTICAL STRUCTURE
AROUND A CUBIC BLUFF BODY IN A CHANNEL
Kurosh Sedighi, Mousa Farhadi
School of Mechanical Engineering, Mazandaran University, P.O.Box 484
Babol, Mazandaran, Iran
E-mail: mousafarhadi@myway.com
Abstract. A numerical investigation of turbulent flow over wall-mounted
cube in a channel was studied by Large Eddy Simulation. The Selective Structure
Function model was used to determinate eddy viscosity appears in the subgrid
scale stress terms in momentum equation. Studies were carried out for the
flows with Reynolds number ranging from 1000 to 40000. To evaluate the
computation results, data was compared with measurement data at Re=40000,
showing a reasonable agreement. In this study the effect of Reynolds numbers
on flow characteristics such as time-averaged streamlines, instantaneous
vorticity and turbulent intensity were investigated. Results of computations
show that the flow with higher Reynolds number has a shorter reattachment
length and by increasing the Reynolds number, the number of horseshoe vortex
in upstream decreases. The negative vorticity near the solid surface is
lifted-up by the positive vorticity in the shear layer and penetrates the
positive vorticity region and causes the detachment of a part of the shear
layer. When the flow pasted around the wall-mounted obstacle, the different
pattern of the streamlines appears at the each sides of the cube which
is changed by increasing the Reynolds number. With increasing the Reynolds
number, turbulent intensity and Reynolds stresses increase at the center
of the vortexes and sides of the cube respectively.
Key Words: Large Eddy Simulation; Selective Structure Function;
Wall-mounted Cube, Reynolds Effects.
TRODIMENZIONALNO ISTRAŽIVANJE VRTLOŽNE
STRUKTURE OKO ISKOŠENE KOCKE U JEDNOM KANALU
Numeričko istraživanje turbulentnog toka preko kocke montirane na zid u
jednom kanalu izvučavala je Simulacija velikog vrtloga. Model selektivne
funkcije strukture se koristi za ispitivanje viskoznosti vrtloga i on se
javlja u članovima jednačine momenta u podrešetkastom naprezanju. Istraživanja
su vršena za protoke sa Rejnoldsovim brojem od 1000 do 40000. Za procenu
kompjuterskih podataka podaci su upoređivani sa podacima merenja pri Re=40000
i pokazali su dobro slaganje. U ovom istraživanju ispitivan je uticaj Rejnoldsovih
brojeva na karakteristike toka kao što su vremenski uprosečene linije toka,
trenutna vrtlogivost i intenzitet turbulencije. Rezultati izračunavanja
pokazuju da Rejnoldsov broj ima kraću dužinu ponovnog pričvršćivanja dok
povećanjem Rejnoldsovog broja opada broj vrtloga u obliku potkovice u gornjem
toku. Negativna vrtlogivost pored čvrstog tela raste sa pozitivnom vrtlogljivošću
u sloju smicanja i prodire u region pozitivne vrtlogljivosti izazivajući
odvajanje jednog dela sloja smicanja. Kada se tok veže oko prepreke na
zidu, javlja se drugačiji obrazac linija toka na svakoj strani kocke što
se, pak, menja promenom Rejnoldsovog broja. Sa povećanjem Rejnoldsovog
broja, intenzitet turbulencije i Rejnoldsov napon se povećavaju u centru
vorteksa i na stranama kocke, respektivno.
Ključne reči: Simulacija velikih vrtloga, selektivna funkcija
strukture, kocka montirana na zidu, Rejnoldsov efekat
