On the Role of Secondary Structures During Leading Edge Vortex Lift Off and Detachment on a Pitching and Plunging Flat Plate

2019 ◽  
pp. 204-213
Author(s):  
Johannes Kissing ◽  
Jochen Kriegseis ◽  
Cameron Tropea
Keyword(s):  
Flat Plate ◽  
Leading Edge ◽  
Secondary Structures ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Lift Off

scholarly journals Insights into leading edge vortex formation and detachment on a pitching and plunging flat plate

2020 ◽  
Vol 61 (9) ◽  
Author(s):  
Johannes Kissing ◽  
Jochen Kriegseis ◽  
Zhenyao Li ◽  
Lihao Feng ◽  
Jeanette Hussong ◽  
...  
Keyword(s):  
Flow Control ◽  
Flat Plate ◽  
Leading Edge ◽  
Secondary Structures ◽  
Control Measures ◽  
Parameter Range ◽  
Leading Edge Vortex ◽  
Topological Features ◽  
Precise Knowledge ◽  
Edge Vortex

Abstract The present study is a prelude to applying different flow control devices on pitching and plunging airfoils with the intention of controlling the growth of the leading edge vortex (LEV); hence, the lift under unsteady stall conditions. As a pre-requisite the parameters influencing the development of the LEV topology must be fully understood and this constitutes the main motivation of the present experimental investigation. The aims of this study are twofold. First, an approach is introduced to validate the comparability between flow fields and LEV characteristics of two different facilities using water and air as working media by making use of a common baseline case. The motivation behind this comparison is that with two facilities the overall parameter range can be significantly expanded. This comparison includes an overview of the respective parameter ranges, control of the airfoil kinematics and careful scrutiny of how post-processing procedures of velocity data from time-resolved particle image velocimetry (PIV) influence the integral properties and topological features used to characterise the LEV development. Second, and based on results coming from both facilities, the appearance of secondary structures and their effect on LEV detachment over an extended parameter range is studied. A Lagrangian flow field analysis based on finite-time Lyapunov Exponent (FTLE) ridges allows precise identification of secondary structures and reveals that their emergence is closely correlated to a vortex Reynolds number threshold computed from the LEV circulation. This threshold is used to model the temporal onset of secondary structures. Further analysis indicates that the emergence of secondary structures causes the LEV to stop accumulating circulation if the shear layer angle at the leading edge of the flat plate has ceased to increase. This information is of particular importance for advanced flow control applications, since efforts to strengthen and/or prolong LEV growth rely on precise knowledge about where and when to apply flow control measures. Graphical abstract

Parameter Variation and the Leading-Edge Vortex of a Rotating Flat Plate

AIAA Journal ◽  
2014 ◽  
Vol 52 (2) ◽  
pp. 348-357 ◽  
Author(s):  
Craig J. Wojcik ◽  
James H. J. Buchholz
Keyword(s):  
Flat Plate ◽  
Leading Edge ◽  
Parameter Variation ◽  
Leading Edge Vortex ◽  
Edge Vortex

Characterizing a burst leading-edge vortex on a rotating flat plate wing

2016 ◽  
Vol 57 (4) ◽  
Author(s):  
Anya R. Jones ◽  
Albert Medina ◽  
Hannah Spooner ◽  
Karen Mulleners
Keyword(s):  
Flat Plate ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

3D Effects in the Wake Vortex Formation of an Elliptic Flat Plate in Hover

2017 ◽  
Author(s):  
Vivek Nair ◽  
Siddarth Chintamani ◽  
B. H. Dennis
Keyword(s):  
Flat Plate ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Elliptic Geometry ◽  
3D Effects ◽  
Edge Vortex ◽  
Formation Number ◽  
Vorticity Transport

A Numerical Analysis is conducted to investigate the Leading Edge Vortex (LEV) dynamics of an elliptic flat plate undergoing 2 dimensional symmetric flapping motion in hover. The plate is modeled with an aspect ratio of 3 and a flapping trajectory resulting in Reynolds number 225 is studied. The leading edge vortex stability is analyzed as a function of the non dimensional formation number and a vorticity transport analysis is carried to understand the flux budgets present. The LEV formation number is found to be 2.6. The results of vorticity analysis show the highly three dimensional nature of the LEV growth for an elliptic geometry.

The role of advance ratio and aspect ratio in determining leading-edge vortex stability for flapping flight

2014 ◽  
Vol 751 ◽  
pp. 71-105 ◽  
Author(s):  
R. R. Harbig ◽  
J. Sheridan ◽  
M. C. Thompson
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Leading Edge Vortex ◽  
Aspect Ratios ◽  
Edge Vortex ◽  
Advance Ratio ◽  
Vorticity Production ◽  
The Stability

AbstractThe effects of advance ratio and the wing’s aspect ratio on the structure of the leading-edge vortex (LEV) that forms on flapping and rotating wings under insect-like flight conditions are not well understood. However, recent studies have indicated that they could play a role in determining the stable attachment of the LEV. In this study, a numerical model of a flapping wing at insect Reynolds numbers is used to explore the effects of these parameters on the characteristics and stability of the LEV. The word ‘stability’ is used here to describe whether the LEV was attached throughout the stroke or if it was shed. It is demonstrated that increasing the advance ratio enhances vorticity production at the leading edge during the downstroke, and this results in more rapid growth of the LEV for non-zero advance ratios. Increasing the wing aspect ratio was found to have the effect of shortening the wing’s chord length relative to the LEV’s size. These two effects combined determine the stability of the LEV. For high advance ratios and large aspect ratios, the LEV was observed to quickly grow to envelop the entire wing during the early stages of the downstroke. Continued rotation of the wing resulted in the LEV being eventually shed as part of a vortex loop that peels away from the wing’s tip. The shedding of the LEV for high-aspect-ratio wings at non-zero advance ratios leads to reduced aerodynamic performance of these wings, which helps to explain why a number of insect species have evolved to have low-aspect-ratio wings.

scholarly journals The role of the leading edge vortex in lift augmentation of steadily revolving wings: a change in perspective

2017 ◽  
Vol 14 (132) ◽  
pp. 20170159 ◽  
Author(s):  
Mostafa R. A. Nabawy ◽  
William J. Crowther
Keyword(s):  
Experimental Data ◽  
Potential Flow ◽  
Normal Force ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Model Parameters ◽  
Force Model ◽  
Leading Edge Vortex ◽  
Edge Vortex

The presence of a stable leading edge vortex (LEV) on steadily revolving wings increases the maximum lift coefficient that can be generated from the wing and its role is important to understanding natural flyers and flapping wing vehicles. In this paper, the role of LEV in lift augmentation is discussed under two hypotheses referred to as ‘additional lift' and ‘absence of stall’. The ‘additional lift' hypothesis represents the traditional view. It presumes that an additional suction/circulation from the LEV increases the lift above that of a potential flow solution. This behaviour may be represented through either the ‘Polhamus leading edge suction' model or the so-called ‘trapped vortex' model. The ‘absence of stall' hypothesis is a more recent contender that presumes that the LEV prevents stall at high angles of attack where flow separation would normally occur. This behaviour is represented through the so-called ‘normal force' model. We show that all three models can be written in the form of the same potential flow kernel with modifiers to account for the presence of a LEV. The modelling is built on previous work on quasi-steady models for hovering wings such that model parameters are determined from first principles, which allows a fair comparison between the models themselves, and the models and experimental data. We show that the two models which directly include the LEV as a lift generating component are built on a physical picture that does not represent the available experimental data. The simpler ‘normal force' model, which does not explicitly model the LEV, performs best against data in the literature. We conclude that under steady conditions the LEV as an ‘absence of stall’ model/mechanism is the most satisfying explanation for observed aerodynamic behaviour.

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