On the Length of the Computational Domain in the DNS of the Heat Transfer in the Fully Developed Turbulent Channel Flow

摘要

Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in the turbulent channel flow was carried out. DNS was performed for Reynolds number Re = 4580 and Prandtl number Pr = 0.71. Two thermal boundary conditions (BCs), isothermal and isoflux, were carried out. Very interesting effect is seen in streamwise temperature auto-correlation functions. While the auto-correlation function for isothermal BC decays close to zero in the observed computational domain, the decay of the auto-correlation function for the isoflux BC is slower and remains well above zero. This could mean that the length of the computational domain for the isoflux BC should be longer in order to satisfy the generally accepted criteria for DNS about the sufficient length of the computational domain. Therefore, another DNS at two times longer computational domain was performed. Two main conclusions were drawn. First, the differences between the DNS in the "standard" length computational domain (approx. 2300 wall units) and the DNS in the extended computational domain (approx. 4600 wall units) did not show any differences larger than the statistical uncertainty for first- and second-order statistics. Second, the periodicity length, which is long enough for the velocity field as an origin of the turbulence, is long enough also for the passive scalar fields, despite the behavior of the streamwise two-point correlation at isoflux boundary condition.