@article{oai:nitech.repo.nii.ac.jp:00005347,
 author = {Tamano, Shinji and Ito, Motoyuki and Hoshizaki, Kenichi and Yokota, Kazuhiko},
 issue = {7},
 journal = {PHYSICS OF FLUIDS},
 month = {Jul},
 note = {Direct numerical simulation of a zero-pressure gradient drag-reducing turbulent boundary layer of homogeneous viscoelastic fluids was performed using constitutive equation models such as the Oldroyd-B and Giesekus models. Mean velocity profiles and turbulence statistics at the different streamwise locations were discussed using both inner and outer scaling. The maximum drag reduction ratio for the Oldroyd-B model, which has the higher elongational viscosity, is larger than for the Giesekus model. The distinct difference in turbulence statistics near the wall between the Oldroyd-B model and Newtonian fluid is observed, as reported in the drag-reducing turbulent channel flow, while in the outer region, distributions of turbulence statistics for the Oldroyd-B model with a drag reduction ratio of about 40% are similar to those for Newtonian fluid. The production term for the turbulent boundary layer does not correspond to the amount of drag reduction, which is consistent with the fact that the streamwise turbulence intensity profile is not a direct indication of the drag reduction. The contribution of the advection term to the budget of streamwise Reynolds normal stress, which does not appear for the turbulent channel flow, is not negligible near the wall for the Oldroyd-B model. For the Oldroyd-B model with a maximum drag reduction ratio of 42%, we can see that quasi-streamwise vortices are weakened and become larger in the streamwise direction, compared to Newtonian fluid. On the other hand, quasi-streamwise vortices for the Giesekus model with a maximum drag reduction ratio of 16% are slightly larger than those for Newtonian fluid. These modifications of near-wall coherent structures are explained by the profile of the trace of mean viscoelastic stress and the elastic energy theory presented by Min et al. [J. Fluid Mech. 486, 213 (2003)] for the drag-reducing turbulent channel flow., application/pdf},
 pages = {075106-1--075106-17},
 title = {Direct  numerical simulation of the drag-reducing turbulent boundary layer of viscoelastic fluid},
 volume = {19},
 year = {2007}
}