Autogenous Suction to Prevent Laminar Boundary-Layer Separation

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Hediye Atik ◽  
Leon van Dommelen
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Laminar Flows ◽  
Computational Techniques ◽  
Pressure Gradients ◽  
Practical Application ◽  
Theoretical Limit ◽  
Local Pressure ◽  
Layer Separation ◽  
Straightforward Application

Boundary-layer separation can be prevented or delayed by sucking part of the boundary layer into the surface, but in a straightforward application the required hydraulics entail significant penalties in terms of weight and cost. By means of computational techniques, this paper explores the possibility of autogenous suction, in which the local pressure differences that lead to separation drive the suction used to prevent it. The chosen examples include steady and unsteady laminar flows around leading edges of thin airfoils. No fundamental theoretical limit to autogenous suction was found in the range of angles of attack that could be studied, but rapidly increasing suction volumes suggest that practical application will become increasingly difficult for more severe adverse pressure gradients.

Boundary Layer Separation Control on a Flat Plate With Adverse Pressure Gradients Using Vortex Generators

2006 ◽  
Author(s):  
Edward Canepa ◽  
Davide Lengani ◽  
Francesca Satta ◽  
Ennio Spano ◽  
Marina Ubaldi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Flat Plate ◽  
Particle Image ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Separation Control ◽  
Pressure Gradients ◽  
Layer Separation ◽  
Image Velocimetry

The continuous tendency in modern aeroengine gas turbines towards reduction of blade count and ducts length may lead to aerodynamic loading increase beyond the limit of boundary layer separation. For this reason boundary layer separation control methods, up to now mostly employed in external aerodynamics, begin to be experimented in internal flows applications. The present paper reports the results of a detailed experimental study on low profile vortex generators used to control boundary layer separation on a large-scale flat plate with prescribed adverse pressure gradients. Inlet turbulent boundary layer conditions and pressure gradients are representative of aggressive turbine intermediate ducts. This activity is part of a joint European research program on Aggressive Intermediate Duct Aerodynamics (AIDA). The pressure gradients on the flat plate are generated by increasing the aperture angle of a movable wall opposite to the flat plate. To avoid separation on the movable wall, boundary layer suction is applied on it. Complementary measurements (surface static pressure distributions, surface flow visualizations by means of wall mounted tufts, instantaneous and time-averaged velocity fields in the meridional and cross-stream planes by means of Particle Image Velocimetry) have been used to survey the flow with and without vortex generators. Three different pressure gradients, which induce turbulent separation in absence of boundary layer control, were tested. Vortex generators height and location effects on separation reduction and pressure recovery increase were investigated. For the most effective VGs configurations detailed analyses of the flow field were performed, that demonstrate the effectiveness of this passive control device to control separation in diffusing ducts. Particle Image Velocimetry vector and vorticity plots illustrate the mechanisms by which the vortex generators transfer momentum towards the surface, re-energizing the near-wall flow and preserving the boundary layer from separation.

Study of Incident Drag Response of Hyperloop Pod Based on Change in Aerodynamic Brake Plate Orientation

2021 ◽  
Author(s):  
Shadman Mahmud ◽  
Adib Adnan ◽  
Shahnoor Shamim Khan ◽  
Md. Hamidur Rahman
Keyword(s):  
Boundary Layer ◽  
Numerical Simulations ◽  
High Speed ◽  
Boundary Layer Separation ◽  
Pressure Gradients ◽  
Transport Models ◽  
Layer Separation ◽  
Passenger Safety ◽  
Speed Flow ◽  
Aerodynamic Brake

The idea for the Hyperloop has received significant attention, with expectations of it becoming a revolutionary and potentially the fastest mode of land transportation on the planet. The low-pressure tube through which the pod travels at expected speeds close to Mach 1.0, presents a unique case among other transport models, and as such, braking of the pod is of critical importance if passenger safety protocols are to be maintained. The high-speed flow around the pod exerts high adverse pressure gradients on the pod surface, resulting in boundary layer separation, increasing drag and affecting the acceleration of the pod. Numerical simulations have shown that the placement of an aerodynamic brake plate on the pod surface at the point at which boundary layer separation occurs provides the necessary drag required for safe deceleration. This study was aimed to find the best angle for the aerodynamic brake positioned at a fixed point on the pod, allowing for the maximum generation of drag, using numerical simulations. After various trials, it was observed that angling the brake 15° backwards while increasing its length to keep incident brake profile constant, the drag value obtained was the highest.

Boundary layer separation induced by successive favorable and adverse pressure gradients

2004 ◽  
Vol 7 (3) ◽  
pp. 174-174
Author(s):  
Savvas S. Xanthos ◽  
Mahmoud Ardebili ◽  
Yiannis Andreopoulos
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Pressure Gradients ◽  
Layer Separation

The boundary layer separation from streamlined surfaces and new ways of its prevention in diffusers

2017 ◽  
Author(s):  
Arkady Zaryankin ◽  
Andrey Rogalev ◽  
Ivan Komarov ◽  
V. Kindra ◽  
S. Osipov
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Layer Separation

scholarly journals Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

2021 ◽  
Vol 11 (6) ◽  
pp. 2593
Author(s):  
Yasir Al-Okbi ◽  
Tze Pei Chong ◽  
Oksana Stalnov
Keyword(s):  
Boundary Layer ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Shear Instability ◽  
Vortical Flow ◽  
High Angle ◽  
High Angle Of Attack ◽  
Layer Separation ◽  
Aerodynamic Performances

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.

On turbulent boundary-layer separation

1968 ◽  
Vol 32 (2) ◽  
pp. 293-304 ◽  
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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