scholarly journals Unsteady separation in vortex-induced boundary layers

2014 ◽  
Vol 372 (2020) ◽  
pp. 20130348 ◽  
Author(s):  
K. W. Cassel ◽  
A. T. Conlisk
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Reynolds Number ◽  
Asymptotic Methods ◽  
Boundary Layer Separation ◽  
Unsteady Boundary Layer ◽  
Layer Separation ◽  
Unsteady Separation ◽  
High Reynolds ◽  
Reynolds Number Flows

This paper provides a brief review of the analytical and numerical developments related to unsteady boundary-layer separation, in particular as it relates to vortex-induced flows, leading up to our present understanding of this important feature in high-Reynolds-number, surface-bounded flows in the presence of an adverse pressure gradient. In large part, vortex-induced separation has been the catalyst for pulling together the theory, numerics and applications of unsteady separation. Particular attention is given to the role that Prof. Frank T. Smith, FRS, has played in these developments over the course of the past 35 years. The following points will be emphasized: (i) unsteady separation plays a pivotal role in a wide variety of high-Reynolds-number flows, (ii) asymptotic methods have been instrumental in elucidating the physics of both steady and unsteady separation, (iii) Frank T. Smith has served as a catalyst in the application of asymptotic methods to high-Reynolds-number flows, and (iv) there is still much work to do in articulating a complete theoretical understanding of unsteady boundary-layer separation.

scholarly journals On the use of lagrangian variables in descriptions of unsteady boundary-layer separation

1990 ◽  
Vol 333 (1631) ◽  
pp. 343-378 ◽  
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Boundary Layer Separation ◽  
Lagrangian Description ◽  
Unsteady Boundary Layer ◽  
Layer Separation ◽  
Unsteady Separation ◽  
Lagrangian Variables ◽  
Classical Boundary ◽  
Layer Region

The lagrangian description of unsteady boundary-layer separation is reviewed from both analytical and numerical perspectives. We explain in simple terms how particle distortion gives rise to unsteady separation, and why a theory centred on lagrangian coordinates provides the clearest description of this phenomenon. Included in the review are some of the more recent results for unsteady three-dimensional compressible separation. The different forms of separation that can arise from symmetries are emphasized. Current work includes a possible description of separation when the detaching vorticity layer exits the classical boundary-layer region, but still remains much closer to the surface than a typical body length-scale.

scholarly journals The onset of instability in unsteady boundary-layer separation

1996 ◽  
Vol 315 ◽  
pp. 223-256 ◽  
Author(s):  
K. W. Cassel ◽  
F. T. Smith ◽  
J. D. A. Walker
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
External Pressure ◽  
Theoretical Description ◽  
Unsteady Boundary Layer ◽  
Layer Separation ◽  
Boundary Layer Equations ◽  
Dimensional Boundary ◽  
High Reynolds ◽  
Inviscid Instability

The process of unsteady two-dimensional boundary-layer separation at high Reynolds number is considered. Solutions of the unsteady non-interactive boundary-layer equations are known to develop a generic separation singularity in regions where the pressure gradient is prescribed and adverse. As the boundary layer starts to separate from the surface, however, the external pressure distribution is altered through viscous—inviscid interaction just prior to the formation of the separation singularity; hitherto this has been referred to as the first interactive stage. A numerical solution of this stage is obtained here in Lagrangian coordinates. The solution is shown to exhibit a high-frequency inviscid instability resulting in an immediate finite-time breakdown of this stage. The presence of the instability is confirmed through a linear stability analysis. The implications for the theoretical description of unsteady boundary-layer separation are discussed, and it is suggested that the onset of interaction may occur much sooner than previously thought.

scholarly journals Some predictions of the attached eddy model for a high Reynolds number boundary layer

2007 ◽  
Vol 365 (1852) ◽  
pp. 807-822 ◽  
Author(s):  
T.B Nickels ◽  
I Marusic ◽  
S Hafez ◽  
N Hutchins ◽  
M.S Chong
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Physical Model ◽  
High Reynolds Number ◽  
Practical Interest ◽  
Physical Explanation ◽  
Wide Range ◽  
High Reynolds ◽  
Random Fluctuations ◽  
Reynolds Number Flows

Many flows of practical interest occur at high Reynolds number, at which the flow in most of the boundary layer is turbulent, showing apparently random fluctuations in velocity across a wide range of scales. The range of scales over which these fluctuations occur increases with the Reynolds number and hence high Reynolds number flows are difficult to compute or predict. In this paper, we discuss the structure of these flows and describe a physical model, based on the attached eddy hypothesis, which makes predictions for the statistical properties of these flows and their variation with Reynolds number. The predictions are shown to compare well with the results from recent experiments in a new purpose-built high Reynolds number facility. The model is also shown to provide a clear physical explanation for the trends in the data. The limits of applicability of the model are also discussed.

Modeling and Simulation of High Reynolds' Number Flows During Reaction Injection Mold Filling

1994 ◽  
Vol 9 (3) ◽  
pp. 279-285 ◽  
Author(s):  
Rahima K. Mohammed ◽  
Tim A. Osswald ◽  
Timothy J. Spiegelhoff ◽  
Esther M. Sun
Keyword(s):  
Reynolds Number ◽  
Modeling And Simulation ◽  
High Reynolds Number ◽  
Mold Filling ◽  
Injection Mold ◽  
High Reynolds ◽  
Reynolds Number Flows
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