Asymptotic description of incipient separation bubble bursting

PAMM ◽  
2012 ◽  
Vol 12 (1) ◽  
pp. 461-462
Author(s):  
Stefan Braun ◽  
Stefan Scheichl ◽  
Alfred Kluwick
Keyword(s):  
Separation Bubble ◽  
Asymptotic Description ◽  
Bubble Bursting ◽  
Incipient Separation

Starting vortex, separation bubbles and stall: a numerical study of laminar unsteady flow around an airfoil

1975 ◽  
Vol 67 (2) ◽  
pp. 227-256 ◽  
Author(s):  
Unmeel B. Mehta ◽  
Zalman Lavan
Keyword(s):  
Numerical Study ◽  
Separation Bubble ◽  
Governing Equations ◽  
Implicit Finite Difference Scheme ◽  
Vortex Separation ◽  
Initial Generation ◽  
Relaxation Procedure ◽  
Implicit Finite Difference ◽  
Incipient Separation ◽  
Successive Relaxation

The stalling characteristics of an airfoil in laminar viscous incompressible fluid are investigated. The governing equations in terms of the vorticity and stream function are solved using an implicit finite-difference scheme and point successive relaxation procedure. The development of the impulsively started flow, the initial generation of circulation, and the behaviour of the forces at large times are studied.Following the impulsive start, the lift is at first very large and then it rapidly drops. The subsequent growth of circulation and lift is associated with the starting vortex. After incipient separation, the lift increases owing to enlargement of the separation bubble and intensification of the flow rotation in it. The extension of this bubble beyond the trailing edge causes it to rupture and brings about the stalling characteristics of the airfoil. Subsequently, new bubbles are formed near the upper surface of the airfoil and are swept away. The behaviour of the lift acting on the airfoil is explained in terms of the strength and sense of these bubbles. The lift increases when attached clockwise bubbles grow and when counterclockwise bubbles are swept away and vice versa.

Marginal Separation Theory

2018 ◽  
Author(s):  
Anatoly I. Ruban
Keyword(s):  
Differential Equation ◽  
Boundary Layer ◽  
Skin Friction ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Sudden Loss ◽  
Bubble Bursting ◽  
Separation Theory ◽  
Interaction Problem

Chapter 5 discusses the ‘short separation bubble’ that forms at the leading edge of an aerofoil when the angle of attack reaches a certain value. It then suggests that the process of the formation of the bubble is described by the Marginal Separation theory, which represents a special version of the triple-deck theory. It then covers how, in this case, the viscous-inviscid interaction problem may be reduced to an integro-differential equation for the skin friction. It discusses how by solving this equation not only the transition from attached to separated flow in the boundary layer be predicted, but also the well-known phenomenon of the ‘bubble bursting’ that leads to a sudden loss of the lift produced by an aerofoil.

scholarly journals Observations of Separated Laminar Flow on Axial Compressor Blading

1975 ◽  
Author(s):  
G. J. Walker
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Critical Reynolds Number ◽  
Separation Bubble ◽  
Axial Compressor ◽  
Theoretical Models ◽  
Bubble Behavior ◽  
Number Range ◽  
Laminar Separation ◽  
Bubble Bursting

This paper describes some detailed observations of separated laminar flow regions on the rotating and stationary blading of a single-stage axial compressor operating at low speed. The data covers the “critical” Reynolds number range where “bursting” of laminar separation bubbles causes a sharp increase in blade profile losses. The experimental results are compared with various empirical correlations and theoretical models proposed by other workers. Horton’s semi-empirical model of separation bubble bursting is broadly supported by the present investigation. However, it appears that some aspects of Horton’s theory require significant modification in order to give an accurate description of the separation bubble behavior on the blades in an axial compressor. It is stressed that correlations of the critical Reynolds number for axial compressor cascades in terms of overall performance parameters should be applied with caution, as they are only likely to be valid for a narrow range of conditions.

Active Forcing of a Pressure-Induced Turbulent Separation Bubble

2020 ◽  
Author(s):  
Abdelouahab T. Mohammed-Taifour ◽  
Arnaud Le Floc'h ◽  
Julien Weiss
Keyword(s):  
Separation Bubble ◽  
Turbulent Separation

Incipient Separation Near Corners

2018 ◽  
Author(s):  
Anatoly I. Ruban
Keyword(s):  
Corner Point ◽  
Analytic Form ◽  
The Body ◽  
Recirculation Region ◽  
Body Contour ◽  
Concave Corner ◽  
Attached Flow ◽  
Surface Deflection ◽  
Interaction Problem ◽  
Incipient Separation

Chapter 4 analyses the transition from an attached flow to a flow with local recirculation region near a corner point of a body contour. It considers both subsonic and supersonic flow regimes, and shows that the flow near a corner can be studied in the framework of the triple-deck theory. It assumes that the body surface deflection angle is small, and formulates the linearized viscous-inviscid interaction problem. Its solution is found in an analytic form. It also presents the results of the numerical solution of the full nonlinear problem. It shows how, and when, the separation region forms in the boundary layer. In conclusion, it suggests that in the subsonic flow past a concave corner, the solution is not unique.

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