A Century of Active Control of Boundary Layer Separation: A Personal View

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively.

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Mitigation of shockwave induced boundary layer separation through a secondary recirculation duct in a hypersonic flow

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/1132/1/012024 ◽

2021 ◽

Vol 1132 (1) ◽

pp. 012024

Author(s):

Kiran Joy Irimpan ◽

Anand Raj Hariharan

Keyword(s):

Boundary Layer ◽

Hypersonic Flow ◽

Boundary Layer Separation ◽

Layer Separation

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On turbulent boundary-layer separation

Journal of Fluid Mechanics ◽

10.1017/s0022112068000728 ◽

1968 ◽

Vol 32 (2) ◽

pp. 293-304 ◽

Cited By ~ 36

Author(s):

V. A. Sandborn ◽

C. Y. Liu

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Turbulent Boundary Layer ◽

Analytical Study ◽

Boundary Layer Separation ◽

Mean Velocity ◽

Laminar Separation ◽

Layer Separation ◽

Turbulent Separation ◽

Separation Model

An experimental and analytical study of the separation of a turbulent boundary layer is reported. The turbulent boundary-layer separation model proposed by Sandborn & Kline (1961) is demonstrated to predict the experimental results. Two distinct turbulent separation regions, an intermittent and a steady separation, with correspondingly different velocity distributions are confirmed. The true zero wall shear stress turbulent separation point is determined by electronic means. The associated mean velocity profile is shown to belong to the same family of profiles as found for laminar separation. The velocity distribution at the point of reattachment of a turbulent boundary layer behind a step is also shown to belong to the laminar separation family.Prediction of the location of steady turbulent boundary-layer separation is made using the technique employed by Stratford (1959) for intermittent separation.

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