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Author:
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ISBN:
Category :
Languages : en
Pages : 20
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Book Description
Receptivity processes by which free-stream disturbances generate Tollmien-Schlichting waves in boundary layers have been analyzed using asymptotic methods for high Reynolds numbers. Vortical and acoustic free-stream disturbances have been considered. Receptivity occurs in the vicinity of the leading edge, and in localized regions further downstream where some feature (e. g., a wall hump) produces a short-scale disturbance to the mean flow. Nonlinear effects related to the free-stream pressure field have been found to play an important role in localized receptivity to vortical disturbances. For leading- edge receptivity, the influences of the body nose radius and aerodynamic loading in the leading-edge region have been analyzed. In the absence of aerodynamic loading, an increase in the body nose radius decreases the leading-edge receptivity coefficient. However, strong aerodynamic loading leads to a dramatic increase in the leading-edge receptivity coefficient, negating the decrease due to a larger nose radius. The propagation of an instability wave past a junction between a rigid wall and a surface with non-zero compliance or admittance has also been analyzed. The junction can cause energy to be scattered from the instability wave to higher eigenmodes, effectively attenuating the instability wave.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 20
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Book Description
Receptivity processes by which free-stream disturbances generate Tollmien-Schlichting waves in boundary layers have been analyzed using asymptotic methods for high Reynolds numbers. Vortical and acoustic free-stream disturbances have been considered. Receptivity occurs in the vicinity of the leading edge, and in localized regions further downstream where some feature (e. g., a wall hump) produces a short-scale disturbance to the mean flow. Nonlinear effects related to the free-stream pressure field have been found to play an important role in localized receptivity to vortical disturbances. For leading- edge receptivity, the influences of the body nose radius and aerodynamic loading in the leading-edge region have been analyzed. In the absence of aerodynamic loading, an increase in the body nose radius decreases the leading-edge receptivity coefficient. However, strong aerodynamic loading leads to a dramatic increase in the leading-edge receptivity coefficient, negating the decrease due to a larger nose radius. The propagation of an instability wave past a junction between a rigid wall and a surface with non-zero compliance or admittance has also been analyzed. The junction can cause energy to be scattered from the instability wave to higher eigenmodes, effectively attenuating the instability wave.
Author: Mohsen Jahanmiri
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659364518
Category :
Languages : en
Pages : 64
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Book Description
Receptivity is the process which describes how environmental disturbances (such as gusts, acoustic waves or wall roughness) are filtered by a boundary layer and turned into downstream growing waves. It is closely related to the identification of initial conditions for the disturbances and requires knowledge of the characteristics of the specific external forcing field. Due to important role of receptivity theory in transition process of boundary layers, quite a few research works have been carried out in past few decades. This research review report tries to highlight the major research activities in this field of study that includes: the theory, different types of receptivity, its effect in three-dimensional boundary layers and receptivity at high speeds.
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ISBN:
Category :
Languages : en
Pages : 85
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This report results from a contract tasking Moscow Institute of Physics and Technology as follows. To predict boundary-layer transition in a rational way and capture its sensitivity to freestream noise, turbulence, surface roughness. steps/gaps/waviness. etc. a toolbox combining receptivity theory with nonlinear Parabolized Stability Equations and Direct Navier-Stokes Simulation is needed. This project addresses this need with theoretical modeling of high speed boundary-layer receptivity to acoustic disturbances as they interact with 3D roughness elements and waviness. The effort is basic. theoretical research on receptivity. Using the multiple-modes method, a compact and computationally robust algorithm providing fast calculations of receptivity characteristics will be developed. This algorithm will be integrated into a computational module that can be linked with a standard stability solver. Receptivity calculations will be made for the conditions relevant to future experiments in the new high Reynolds-number. Mach-6. quiet Ludwieg' tube of Purdue University. This will help to formulate recommendations for design of receptivity experiments and interpretation of the data. The results of the project can also be applied at the component level to assess laminar flow control concepts.
Author: Meelan Choudhari
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 44
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Author: Meelan Choudhari
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Ian John Sobey
Publisher: OUP Oxford
ISBN: 9780198506751
Category : Mathematics
Languages : en
Pages : 350
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Book Description
One of the major achievements in fluid mechanics in the last quarter of the twentieth century has been the development of an asymptotic description of perturbations to boundary layers known generally as 'triple deck theory'. These developments have had a major impact on our understanding of laminar fluid flow, particularly laminar separation. It is also true that the theory rests on three quarters of a century of development of boundary layer theory which involves analysis, experimentation and computation. All these parts go together, and to understand the triple deck it is necessary to understand which problems the triple deck resolves and which computational techniques have been applied. This book presents a unified account of the development of laminar boundary layer theory as a historical study together with a description of the application of the ideas of triple deck theory to flow past a plate, to separation from a cylinder and to flow in channels. The book is intended to provide a graduate level teaching resource as well as a mathematically oriented account for a general reader in applied mathematics, engineering, physics or scientific computation.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 7
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The investigation of mechanisms of excitation of the boundary-layer instability waves by various external perturbations represents an important aspect of the laminar-turbulent transition problem and has a crucial significance for both basic research of transition and practical applications. A review of recent studies in this field related to 3D receptivity problems for 2D and 3D boundary layers can be found. Most of previous experimental investigations were devoted to the receptivity to surface perturbations (roughness and vibrations) and to acoustic waves. Meanwhile, the excitation of instability waves by free-stream turbulence can also play a very important role and influence the transition process. The present paper is devoted to an experimental investigation of the 3D receptivity of Blasius boundary layer to non-stationary vortical free-stream disturbances due to their scattering on localized (in streamwise and spanwise directions) surface vibrations. There is only one available quantitative experimental study of a similar receptivity problem performed for unsteady free-stream vortices. A scattering of a weak vortex street (with 2D spanwise vorticity) on a localized two-dimensional surface roughness has been studied in this work in the Blasius flow. The results of this experiment were found to be in a good agreement with the 2D receptivity theory. Three-dimensional receptivity to non-stationary free-stream vortices has not been studied in previous experiments at all. The scattering of free-stream vortices on surface vibrations was not studied even for purely two-dimensional case.
Author: C. E. Grosch
Publisher:
ISBN:
Category : Turbulent boundary layer
Languages : en
Pages : 6
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Author: Meelan Choudhari
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 40
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Author: National Aeronautics and Space Adm Nasa
Publisher:
ISBN: 9781729112342
Category :
Languages : en
Pages : 26
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Book Description
Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments. Reed, Helen L. Unspecified Center ...
