Zagumennyi I. Interaction of turbulent boundary layer with a viscoelastic coating of variable thickness

The thesis is devoted to the development of energetic model of turbulent boundary layer on the deformable surface. This model is based on the Reynolds stress transfer turbulence model modified for wall-bounded flows which takes into account the kinematical and dynamic interactions of turbulent flow and a viscoelastic coating. The boundary conditions for turbulent boundary layer on a compliant surface are determined on the basis of a numerical solution of non-stationary three-dimensional problem on oscillations of isotropic viscoelastic coating of variable thickness, finite length and width under the action of arbitrary local impulse load. The parameters of this load are determined on the basis of experimental measurements of intensity and space-time scales of the discrete bursts in a viscous sublayer of turbulent boundary layer. The kinematical and dynamical characteristics of the coating are obtained as functions of the mechanical parameters of the coating, its geometry, thickness and the load location. The conditions for maximal absorption of the impulse energy are determined depending on the mechanical and geometric parameters of the layer and duration of the load action. It is revealed that the coating ceases to accept energy of external disturbance and begins to accomplish damping oscillations with a period of thickness resonance with arrival of the normal wave at the surface as reflected from the lower rigid boundary. This fact allows to determine the parameters of a coating with fixed thickness which maximally absorbs energy of external disturbance. The influence of viscoelastic coating's dimension in the transversal direction as well as the law of its thickness variation on forming of the directed wave field on the surface is investigated. It is shown that a surface wave field codirectional with the fluid flow can be obtained by varying of viscoelastic coating's geometry that leads to the least disturbing influence on the flow. In the frame of the proposed model of interaction of flow and deformable body the averaged, pulsating and integral characteristics of turbulent boundary layer over the surface of viscoelastic coatings of different properties are calculated.