

Artikel
Convergence of numerical simulations of turbulent wallbounded flows and mean crossflow structure of rectangular ducts
Författare: 
Vinuesa, R., Prus, C., Schlatter, P., Nagib, H.M. 
Dokumenttyp: 
Artikel 
Tillstånd: 
Publicerad 
Tidskrift: 
Meccanica 
Volym: 
51
30253042 
År: 
2016 
AbstractConvergence criteria for direct numerical simulations (DNSs) of turbulent channel and duct flows are proposed. The convergence indicator for channels is defined as the deviation of the nondimensional total shearstress profile with respect to a linear profile, whereas the one for the duct is based on a nondimensional streamwise momentum balance at the duct centerplane. We identify the starting (T S) and averaging times (T A) necessary to obtain sufficiently converged statistics, and also find that optimum convergence rates are achieved when the spacing in time between individual realizations is below ?t + = 17. The inplane structure of the flow in turbulent ducts is also assessed by analyzing square ducts at Re ?,c 180 and 360 and rectangular ducts with aspect ratios 3 and 10 at Re ?,c 180. Identification of coherent vortices shows that nearwall streaks are located in all the duct cases at a wallnormal distance of y + 40 as in Pinelli et al. (J. Fluid Mech. 644, 107–122, 2010). We also find that largescale motions play a crucial role in the streamline pattern of the secondary flow, whereas nearwall structures highly influence the streamwise vorticity pattern. These conclusions extend the findings by Pinelli et. al. to other kinds of largescale motions in the flow through the consideration of wider ducts. They also highlight the complex and multiscale nature of the secondary flow of second kind in turbulent duct flows.

