scholarly journals Acoustic excitation of Tollmien–Schlichting waves due to localised surface roughness

2020 ◽  
Vol 895 ◽  
Author(s):  
Marco Placidi ◽  
Michael Gaster ◽  
Chris J. Atkin
Keyword(s):  
Surface Roughness ◽  
Acoustic Excitation ◽  
Tollmien Schlichting ◽  
Image Position

Acoustic receptivity and evolution of two-dimensional and oblique disturbances in a Blasius boundary layer

2001 ◽  
Vol 432 ◽  
pp. 69-90 ◽  
Author(s):  
RUDOLPH A. KING ◽  
KENNETH S. BREUER
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Acoustic Wave ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Surface Waviness ◽  
S Wave ◽  
Boundary Layer Instability ◽  
Blasius Boundary Layer ◽  
Tollmien Schlichting

An experimental investigation was conducted to examine acoustic receptivity and subsequent boundary-layer instability evolution for a Blasius boundary layer formed on a flat plate in the presence of two-dimensional and oblique (three-dimensional) surface waviness. The effect of the non-localized surface roughness geometry and acoustic wave amplitude on the receptivity process was explored. The surface roughness had a well-defined wavenumber spectrum with fundamental wavenumber kw. A planar downstream-travelling acoustic wave was created to temporally excite the flow near the resonance frequency of an unstable eigenmode corresponding to kts = kw. The range of acoustic forcing levels, ε, and roughness heights, Δh, examined resulted in a linear dependence of receptivity coefficients; however, the larger values of the forcing combination εΔh resulted in subsequent nonlinear development of the Tollmien–Schlichting (T–S) wave. This study provides the first experimental evidence of a marked increase in the receptivity coefficient with increasing obliqueness of the surface waviness in excellent agreement with theory. Detuning of the two-dimensional and oblique disturbances was investigated by varying the streamwise wall-roughness wavenumber αw and measuring the T–S response. For the configuration where laminar-to-turbulent breakdown occurred, the breakdown process was found to be dominated by energy at the fundamental and harmonic frequencies, indicative of K-type breakdown.

Influence of selective laser melting scanning speed parameter on the surface morphology, surface roughness, and micropores for manufactured Ti6Al4V parts

2020 ◽  
Vol 35 (15) ◽  
pp. 2025-2035
Author(s):  
Mohd Faizal Sadali ◽  
Mohamad Zaki Hassan ◽  
Fauzan Ahmad ◽  
Hafizal Yahaya ◽  
Zainudin A Rasid
Keyword(s):  
Surface Roughness ◽  
Surface Morphology ◽  
Selective Laser Melting ◽  
Scanning Speed ◽  
Laser Melting ◽  
Speed Parameter ◽  
Image Position

Abstract

Representing surface roughness in eddy resolving simulation

2020 ◽  
Vol 897 ◽  
Author(s):  
Joel Varghese ◽  
Paul A. Durbin
Keyword(s):  
Surface Roughness ◽  
Image Position

The fatigue failure analysis and fatigue life prediction model of FV520B-I as a function of surface roughness in HCF regime

2017 ◽  
Vol 32 (3) ◽  
pp. 634-643 ◽  
Author(s):  
Jin-long Wang ◽  
Yuan-liang Zhang ◽  
Qing-chen Zhao ◽  
Min Zhang ◽  
Ze-ming Guan ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Prediction Model ◽  
Failure Analysis ◽  
Fatigue Failure ◽  
Life Prediction ◽  
Fatigue Life Prediction ◽  
Image Position ◽  
Life Prediction Model

Abstract

The effect of small surface perturbations on the pulsatile boundary layer on a semi-infinite flat plate

1988 ◽  
Vol 197 ◽  
pp. 259-293 ◽  
Author(s):  
P. W. Duck
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Incompressible Flows ◽  
Fourier Transforms ◽  
Acoustic Excitation ◽  
Main Body ◽  
Small Surface ◽  
Boundary Layer Equations ◽  
Surface Distortion ◽  
Tollmien Schlichting

The laminar pulsatile flow over a semi-infinite flat plate, on which is located a small (steady) surface distortion is investigated; triple-deck theory provides the basis for the study. The problem is of direct relevance to the externally imposed acoustic excitation of boundary layers. The investigation is primarily numerical and involves the solution of the nonlinear, unsteady boundary-layer equations which arise from the lower deck. The numerical method involves the use of finite differencing in the transverse direction, Crank-Nicolson marching in time, and Fourier transforms in the streamwise direction, and as such is an extension of the spectral method of Burggraf & Duck (1982). Supersonic and incompressible flows are studied. A number of the computations presented suggest that the small surface distortion can excite a large-wavenumber, rapidly growing instability, leading to a breakdown of the solution, with the wall shear at a point seeming to increase without bound as a finite time is approached. Rayleigh modes for the basic (undisturbed) velocity profile are computed and there is some correlation between the existence and magnitude of the growth rate of these unstable modes, and the occurrence of the apparent singularity. Streamline plots indicate that this phenomenon is linked to the formation of closed (or ‘cats-eye’) eddies in the main body of the boundary layer, away from the wall. Tollmien-Schlichting instabilities are clearly seen in the case of incompressible flows.

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