Deformation of viscoelastic coating in a turbulent flow
V.M. Kulik
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia, kulik@itp.nsc.ru
Keywords: compliant coating, turbulent flow, pressure pulsations, 2D model of deformation, energy dissipation, Reynolds stresses
Pages: 43-56
Abstract
The rate and amplitude of compliant coating deformation by turbulent pressure pulsations were calculated. Complex compliance determined by a 2D model has two components: along and across the coating. Dependence of the components of dimensionless compliance on the wavelength ⎯ coating thickness ratio was determined for 0.3 < λ/H < 30 and dependence of these components on the ratio of flow velocity to velocity of wave propagation was determined for 0.1 < V/C < 10.
Deformation amplitude and rate of surface displacement for the hard compliant coatings which can be used in practice were calculated within the range of 5-55 m/s for the water and air turbulent flow. The effects of the loss tangent and Poisson's ratio of the coating material were also studied.
It is shown that the mean-square displacement of their surface does not exceed the thickness of a viscous sublayer. However, the velocity of surface motion is comparable with velocity pulsations in a boundary layer near a wall. This can be a reason for drag reduction on a compliant wall. The calculated value of ratio between energy absorbed by the wall and energy dissipated within the flow because of drag was 10−4 for water and 10−6 for air. This estimate does not confirm the hypothesis explaining drag reduction by energy takeoff from the flow.
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