## EFFECT OF RHEOLOGICAL PARAMETERS ON DRAG-REDUCING TURBULENT BOUNDARY LAYER OF VISCOELASTIC FLUID
## ResumoDirect numerical simulation of a zero-pressure gradient drag-reducing turbulent boundary layer of viscoelastic solutions was performed at momentum-thickness Reynolds number We = 25 using constitutive equation models such as the Oldroyd-B model and Giesekus model (the mobility factor α = 0.001, 0.002, 0.005, 0.01) in which the rheological properties are different. It is found that the maximum drag reduction ratio %DR for the Oldroyd-B model is larger than that for the Giesekus model even at the same Weissenberg number (We = 25), although the maximum %DR for the Giesekus model approaches one for the Oldroyd-B model as a decreases from 0.01 to 0.001. For the Giesekus model with α = 0.001, we can see that quasi-streamwise vortices are weakened and become larger in the streamwise direction, compared to the Giesekus model with α =0.01. The present results indicate that the higher elongational viscosity yields the larger drag reduction ratio, so that turbulence statistics and structures are modified more clearly in the drag-reducing turbulent boundary layer. |

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