Detailed characteristics of the near-wall flow containing unsteady viscous sublayer in smooth channel

Structural mechanics

Taking into consideration the experimental data on the longitudinal and the normal to the wall velocity fluctuations and the correlation coefficient between the fluctuations, the turbulent and viscous friction components near the wall were determined. Based on the adjusted value of the components of viscous friction there was obtained thickness of the viscous flow, depending on the drag coefficient. The unsteady flow in the viscous sublayer based on Einstein and Lee's model modified by introducing the changing velocity at the upper boundary of the viscous sublayer was considered. The solution to the dynamic equation in the form of the velocity profile, depending on time and distance from the wall was obtained. This velocity profile may be used for the buffer region, in which a viscous flow is transformed into a turbulent one. Von-Karman's parameter and the profile constant were determined on the basis of LDA measurements in the smooth channel. According to the intermittent flow model for the buffer region, a viscous flow is destroyed and replaced with a turbulent flow with a logarithmic velocity profile. To determine velocity distribution in the buffer region it is proposed to use a gamma intermittency factor, allowing for time of the turbulent flow, divided by the total time of the process. The analysis shows that the intermittency factor varies with the distance from the wall, and it is quantitatively similar to the error integral. The obtained velocitу distribution has been confirmed by many authors' measurements.