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.

Instantaneous topology of the unsteady leading-edge vortex at high angle of attack

AIAA Journal ◽  
1993 ◽  
Vol 31 (8) ◽  
pp. 1384-1391 ◽  
Author(s):  
C. Magness ◽  
O. Robinson ◽  
D. Rockwell
Keyword(s):  
Angle Of Attack ◽  
Leading Edge ◽  
High Angle ◽  
High Angle Of Attack ◽  
Leading Edge Vortex ◽  
Edge Vortex

scholarly journals Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

2015 ◽  
Vol 12 (105) ◽  
pp. 20150051 ◽  
Author(s):  
Jan W. Kruyt ◽  
GertJan F. van Heijst ◽  
Douglas L. Altshuler ◽  
David Lentink
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Angle Of Attack ◽  
Radial Distance ◽  
Leading Edge ◽  
High Angle ◽  
High Angle Of Attack ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Low Aspect Ratio Wings

Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack.

Experimental and Computational Investigation of a Simplified Geometry of an Engine/Pylon/Wing Installation at High-Lift Flight Conditions

2013 ◽  
Author(s):  
Matthieu Lucas ◽  
Yannick Bury ◽  
Cyril Bonnaud ◽  
Laurent Joly
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Longitudinal Vortex ◽  
Vortical Flow ◽  
Stream Velocity ◽  
Piv Measurements ◽  
Comprehensive Knowledge ◽  
Oil Flow

This paper focuses on the numerical and experimental characterization of the vortex structures that develop along a simplified geometry of a wing equipped with pylon-mounted engine at low speed/high angle of attack flight conditions. In these conditions, the presence of the engine installation under the wing induces a complex and unsteady vortical flow field at the nacelle/pylon/wing junctions which interacts with the upper wing boundary layer and leads to a drop of aircraft performances. In order to gain insight into the physics driving this interaction, it is proposed to isolate its fundamental mechanisms by simplifying the problem. The parameters of interest that led to the simplification of the model are first described. As a first step into a more comprehensive knowledge of this complex physics, this study is initially conducted at a Reynolds number of 200000, based on the chord wing and on the free stream velocity. Two configurations of angle of attack and sideslip angles (α = 8°/β = 0° and α = 8°/β = 30°) have been investigated. This work relies on unsteady RANS computations, oil flow visualizations and 3C-PIV measurements. The vortex dynamics thus produced is described in terms of vortex core position, intensity, size and turbulent intensity thanks to a vortex tracking post-processing algorithm. In addition, the analysis of the velocity flow field obtained from the PIV measurements will highlight the influence of the longitudinal vortex issued from the pylon/wing junction on the separation process of the boundary layer near the upper wing leading-edge.

On the Vortex Breakdown Phenomenon in High Angle of Attack Flows Over Delta Wing Geometries

2014 ◽  
Author(s):  
Eric D. Robertson ◽  
Varun Chitta ◽  
D. Keith Walters ◽  
Shanti Bhushan
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
High Angle Of Attack ◽  
Eddy Simulation ◽  
Wing Model

Using computational methods, an investigation was performed on the physical mechanisms leading to vortex breakdown in high angle of attack flows over delta wing geometries. For this purpose, the Second International Vortex Flow Experiment (VFE-2) 65° sweep delta wing model was studied at a root chord Reynolds number (Recr) of 6 × 106 at various angles of attack. The open-source computational fluid dynamics (CFD) solver OpenFOAM was used in parallel with the commercial CFD solver ANSYS® FLUENT. For breadth, a variety of classic closure models were applied, including unsteady Reynolds-averaged Navier-Stokes (URANS) and detached eddy simulation (DES). Results for all cases are analyzed and flow features are identified and discussed. The results show the inception of a pair of leading edge vortices originating at the apex for all models used, and a region of steady vortical structures downstream in the URANS results. However, DES results show regions of massively separated helical flow which manifests after vortex breakdown. Analysis of turbulence quantities in the breakdown region gives further insight into the mechanisms leading to such phenomena.

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