A theoretical mode for the instability of turbulent boundary layer over compliant surface

2001 ◽  
Vol 17 (2) ◽  
pp. 133-141 ◽  
Author(s):  
Zhao Hanzhong ◽  
Yeo Khoon Seng
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Compliant Surface

The Response of Elastic and Viscoelastic Surfaces to a Turbulent Boundary Layer

1986 ◽  
Vol 53 (1) ◽  
pp. 206-212 ◽  
Author(s):  
Mohamed Gad-el-Hak
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Surface Deformation ◽  
Phase Speed ◽  
Instability Waves ◽  
Compliant Surface ◽  
Wave Characteristics ◽  
Highly Nonlinear ◽  
Nonlinear Static ◽  
High Phase

The unstable response of elastic and viscoelastic surfaces to a turbulent boundary layer was experimentally investigated in an 18-m towing tank. The compliant surface deformation was measured using a remote optical technique. The “Laser Displacement Gauge” employs a Reticon camera equipped with a linear array of 256 photodiodes spaced 25 microns apart. The device was used to measure the characteristics of two classes of hydroelastic instability waves that form on elastic or viscoelastic surfaces as a reuslt of the interaction with a turbulent boundary layer. The instability waves developing on an elastic surface are symmetric and have a relatively high phase speed and a small wavelength, as compared to the slow and highly nonlinear “static-divergence” waves observed on the viscoelastic surface. The experimentally determined wave characteristics are compared to existing theories on compliant surface instabilities.

On the interaction of compliant coatings with boundary-layer flows

1984 ◽  
Vol 140 ◽  
pp. 257-280 ◽  
Author(s):  
Mohamed Gad-El-Hak ◽  
Ron F. Blackwelder ◽  
James J. Riley
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Surface Deformation ◽  
Water Channel ◽  
Wave Structure ◽  
Boundary Layer Flows ◽  
Instability Waves ◽  
Compliant Surface ◽  
Onset Velocity ◽  
Low Speed Streaks

The interactions of compliant coatings with laminar, transitional and turbulent boundary layers are investigated. A 2 m long flat plate is towed in the range of speeds of 20–140 cm/s in an 18 m water channel using a carriage riding on an oil film. Isotropic and anistropic compliant coatings are used to cover about 20% of the working Plexiglas surface. The compliant material used is a viscoelastic plastisol gel produced by heating a mixture of polyvinyl chloride resin, a plasticizer and a stabilizer, and allowing them to gel. The shear modulus of rigidity of the plastisol was varied by changing the percentage of PVC in the mix. Anisotropy is introduced by placing the plastisol on a rubber surface having longitudinal grooves scaled with the low-speed streaks in the turbulent boundary layer. The most pronounced effect of the surface compliance in a turbulent boundary layer is a hydroelastic instability in the form of a spanwise wave structure on the compliant surface. The compliant-surface deformation was measured using a novel remote optical technique. The onset speed of the hydroelastic instability waves depends on the thickness and the modulus of rigidity of the plastisol. Their wavelength, wave speed and amplitude are found to depend on these plastisol parameters as well as on the towing speed. In a laminar boundary layer with freestream speeds of over twice the corresponding onset velocity for the turbulent case, no similar instability is observed.

Turbulent boundary layer over a compliant surface: absolute and convective instabilities

2001 ◽  
Vol 449 ◽  
pp. 141-168 ◽  
Author(s):  
K. S. YEO ◽  
H. Z. ZHAO ◽  
B. C. KHOO
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Reynolds Stress ◽  
Temporal Perspective ◽  
Mean Velocity ◽  
Compliant Surface ◽  
Convective Instabilities ◽  
Compliant Surfaces ◽  
The Mean ◽  
Spatio Temporal

A theoretical model for the instability of two-dimensional turbulent boundary layer over compliant surfaces is described. The principal Reynolds stress is modelled by a well-established mixing-length eddy-viscosity formulation of van Driest. The perturbations of the mean velocity and Reynolds stress fields are coupled via the turbulence model. The investigation of instability is carried out from a time-asymptotic spatio-temporal perspective that classifies instabilities as being either convective or absolute. The occurrence of convective and absolute instabilities over viscoelastic compliant layers is elucidated. Compliant surfaces with low damping are susceptible to convective instability, which gives way to an absolute instability when the surfaces become highly damped. The theoretical results are compared against experimental observations of surface waves on elastic and viscoelastic compliant layers.

scholarly journals Experiments and Modeling of a Compliant Wall Response to a Turbulent Boundary Layer with Dynamic Roughness Forcing

Fluids ◽  
2021 ◽  
Vol 6 (5) ◽  
pp. 173
Author(s):  
David P. Huynh ◽  
Yuting Huang ◽  
Beverley J. McKeon
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Image Correlation ◽  
Normal Velocity ◽  
Compliant Surface ◽  
Dynamic Roughness ◽  
Image Velocimetry ◽  
Compliant Wall ◽  
Surface Measurements ◽  
Wall Compliance

The response of a compliant surface in a turbulent boundary layer forced by a dynamic roughness is studied using experiments and resolvent analysis. Water tunnel experiments are carried out at a friction Reynolds number of Reτ≈410, with flow and surface measurements taken with 2D particle image velocimetry (PIV) and stereo digital image correlation (DIC). The narrow band dynamic roughness forcing enables analysis of the flow and surface responses coherent with the forcing frequency, and the corresponding Fourier modes are extracted and compared with resolvent modes. The resolvent modes capture the structures of the experimental Fourier modes and the resolvent with eddy viscosity improves the matching. The comparison of smooth and compliant wall resolvent modes predicts a virtual wall feature in the wall normal velocity of the compliant wall case. The virtual wall is revealed in experimental data using a conditional average informed by the resolvent prediction. Finally, the change to the resolvent modes due to the influence of wall compliance is studied by modeling the compliant wall boundary condition as a deterministic forcing to the smooth wall resolvent framework.

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