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 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.

Comparison of Experimental and Computational Shock Structure in a Transonic Compressor Rotor

1981 ◽  
Vol 103 (1) ◽  
pp. 78-88
Author(s):  
G. Haymann-Haber ◽  
W. T. Thompkins
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Inviscid Flow ◽  
Boundary Layer Separation ◽  
Shock Strength ◽  
Layer Separation ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Pressure Peak ◽  
Rotor Losses

Measurement of passage shock strength in a transonic compressor rotor using a gas fluorescent technique revealed an unexpected variation in shock strength in the radial direction. An axisymmetric idealization would normally predict that the passage shock strength would gradually weaken when moving radially inward until disappearing at the sonic radius. However, the measurements indicated a sharp peak in strength at the nominal sonic radius. Blade boundary layer separation originating at this point accounts for about one half of the total rotor losses. A numerical computation of the three-dimensional inviscid flow, using time-marching techniques, has accurately predicted in general the radial and tangential variations in passage shock strength and in particular the sharp pressure peak at the nominal sonic radius. The overall shock strength was somewhat over-predicted, but this overprediction may be the result of boundary layer separation in the experiment. This paper presents comparisons between the optical density measurements and computational results and in addition a short analytical discussion which demonstrates that the sharp shock strength rise may occur in many transonic compressor rotors.

Boundary-Layer Separation From Downstream Moving Boundaries

1973 ◽  
Vol 40 (2) ◽  
pp. 369-374 ◽  
Author(s):  
D. P. Telionis ◽  
M. J. Werle
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Adverse Pressure Gradient ◽  
Theoretical Models ◽  
Boundary Layer Separation ◽  
Moving Boundaries ◽  
Unsteady Boundary Layer ◽  
Layer Separation ◽  
Boundary Layer Equations ◽  
Type Singularity

The laminar boundary-layer equations for incompressible flow with a mild adverse pressure gradient were numerically solved for flows over downstream moving boundaries. It was demonstrated that the vanishing of skin friction in this case is not related to separation.2 Indeed the integration proceeds smoothly through a point of vanishing skin friction and further downstream a Goldstein-type singularity appears at a station where all the properties of separation according to the model of Moore, Rott, and Sears are present. It is also numerically demonstrated that the singular behavior is not uniform with n, the distance perpendicular to the wall, but it is initiated at a point away from the wall leaving below a region of nonsingular flow. The foregoing points provide numerical justification of the general theoretical models of unsteady boundary-layer separation suggested by Sears and Telionis.

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