A scaling for vortex formation on swept and unswept pitching wings

2017 ◽  
Vol 832 ◽  
pp. 697-720 ◽  
Author(s):  
Kyohei Onoue ◽  
Kenneth S. Breuer
Keyword(s):  
Control Volume ◽  
Vortex Formation ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Leading Edge ◽  
Sweep Angle ◽  
Reduced Frequency ◽  
Vortex Formation Time ◽  
The Stability ◽  
Vorticity Transport

We examine the dynamics of the leading-edge vortex (LEV) on a rapidly pitching plate with the aim of elucidating the underlying flow physics that dictates the stability and circulation of the LEV. A wide variety of flow conditions is considered in the present study by systematically varying the leading-edge sweep angle ($\unicode[STIX]{x1D6EC}=0^{\circ }$, $11.3^{\circ }$, $16.7^{\circ }$) and the reduced frequency ($f^{\ast }=0.064{-}0.151$), while keeping the pitching amplitude and the Reynolds number fixed. Tomographic particle image velocimetry is used to characterise the three-dimensional fluid motion inside the vortex core and its relation to the LEV stability and growth. A series of control volume analyses are performed to quantify the relative importance of the vorticity transport phenomena taking place inside the LEV to the overall vortex development. We show that, near the wing apex where tip effects can be neglected, the vortex develops in a nominally two-dimensional manner, despite the presence of inherently three-dimensional vortex dynamics such as vortex stretching and compression. Furthermore, we demonstrate that the vortex formation time and circulation growth are well-described by the principles of optimal vortex formation number, and that the occurrence of vortex shedding is dictated by the relative energetics of the feeding shear layer and the resulting vortex.

Vortex formation on surging aerofoils with application to reverse flow modelling

2018 ◽  
Vol 859 ◽  
pp. 59-88 ◽  
Author(s):  
Philip B. Kirk ◽  
Anya R. Jones
Keyword(s):  
Surface Pressure ◽  
Reverse Flow ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Field Measurements ◽  
Reduced Frequency ◽  
Advance Ratio ◽  
Convection Speed

The leading-edge vortex (LEV) is a powerful unsteady flow structure that can result in significant unsteady loads on lifting blades and wings. Using force, surface pressure and flow field measurements, this work represents an experimental campaign to characterize LEV behaviour in sinusoidally surging flows with widely varying amplitudes and frequencies. Additional tests were conducted in reverse flow surge, with kinematics similar to the tangential velocity profile seen by a blade element in recent high-advance-ratio rotor experiments. General results demonstrate the variability of LEV convection properties with reduced frequency, which greatly affected the average lift-to-drag ratio in a cycle. Analysis of surface pressure measurements suggests that LEV convection speed is a function only of the local instantaneous flow velocity. In the rotor-comparison tests, LEVs formed in reverse flow surge were found to convect more quickly than the corresponding reverse flow LEVs that form on a high-advance-ratio rotor, demonstrating that rotary motion has a stabilizing effect on LEVs. The reverse flow surging LEVs were also found to be of comparable strength to those observed on the high-advance-ratio rotor, leading to the conclusion that a surging-wing simplification might provide a suitable basis for low-order models of much more complex three-dimensional flows.

Determining the relative stability of leading-edge vortices on nominally two-dimensional flapping profiles

2015 ◽  
Vol 766 ◽  
pp. 611-625 ◽  
Author(s):  
Jaime G. Wong ◽  
David E. Rival
Keyword(s):  
Relative Stability ◽  
Particle Tracking Velocimetry ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reduced Frequency ◽  
Image Velocimetry ◽  
Vortex Size ◽  
Spanwise Vorticity ◽  
Vorticity Transport ◽  
Leading Edge Vortices

AbstractIt is hypothesized that the relative stability of leading-edge vortices (LEVs) on flapping profiles can be improved by moderating LEV growth through spanwise vorticity convection and vortex stretching. Moreover, it is hypothesized that the reduced frequency $k$ and profile sweep ${\it\Lambda}$ are critical in predicting relative LEV stability as determined by the aforementioned effects. These hypotheses are then confirmed experimentally with phase-averaged particle image velocimetry (PIV) and three-dimensional particle tracking velocimetry. In particular, more stable LEVs are observed at higher reduced frequencies, which is argued to represent the ratio between the limiting vortex size and the rate of vorticity feeding. The introduction of profile sweep increased both relative LEV stability and spanwise vorticity transport. It is thought that spanwise vorticity transport improved LEV stability by acting as a sink for vorticity generated in the leading-edge shear layer.

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.

Experimental and Theoretical Investigation of the Supersonic Boundary Layer Stability on the Swept Wing

2008 ◽  
Vol 3 (3) ◽  
pp. 34-38
Author(s):  
Sergey A. Gaponov ◽  
Yuri G. Yermolaev ◽  
Aleksandr D. Kosinov ◽  
Nikolay V. Semionov ◽  
Boris V. Smorodsky
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Supersonic Boundary Layer ◽  
Mean Flow ◽  
Swept Wing ◽  
Wing Model ◽  
Dimensional Boundary ◽  
The Stability ◽  
Good Agreement

Theoretical and an experimental research results of the disturbances development in a swept wing boundary layer are presented at Mach number М = 2. In experiments development of natural and small amplitude controllable disturbances downstream was studied. Experiments were carried out on a swept wing model with a lenticular profile at a zero attack angle. The swept angle of a leading edge was 40°. Wave parameters of moving disturbances were determined. In frames of the linear theory and an approach of the local self-similar mean flow the stability of a compressible three-dimensional boundary layer is studied. Good agreement of the theory with experimental results for transversal scales of unstable vertices of the secondary flow was obtained. However the calculated amplification rates differ from measured values considerably. This disagreement is explained by the nonlinear processes observed in experiment

scholarly journals Fin sweep angle does not determine flapping propulsive performance

2020 ◽  
Author(s):  
Andhini N. Zurman-Nasution ◽  
Bharathram Ganapathisubramani ◽  
Gabriel D. Weymouth
Keyword(s):  
Correlation Coefficient ◽  
Large Range ◽  
Three Dimensional ◽  
Leading Edge ◽  
Potential Sweep ◽  
Sweep Angle ◽  
Propulsive Performance ◽  
Maximum Angle ◽  
And Robotics ◽  
Three Dimensional Simulations

The importance of the leading-edge sweep angle of propulsive surfaces used by unsteady swimming and flying animals has been an issue of debate for many years, spurring studies in biology, engineering, and robotics with mixed conclusions. In this work we provide results from an extensive set of three-dimensional simulations of finite foils undergoing tail-like (pitch-heave) and flipper-like (twist-roll) kinematics for a range of sweep angles while carefully controlling all other parameters. No significant change in force and power is observed for tail-like motions as the sweep angle increases, with a corresponding efficiency drop of only ≈ 2%. Similar findings are seen in flipper-like motion and the overall correlation coefficient between sweep angle and propulsive performance is 0.1-6.7%. This leads to a conclusion that fish tails or mammal flukes can have a large range of potential sweep angles without significant negative propulsive impact. A similar conclusion applies to flippers; although there is a slight benefit to avoid large sweep angles for flippers, this could be easily compensated by adjusting other hydrodynamics parameters such as flapping frequency, amplitude and maximum angle of attack to gain higher thrust and efficiency.

Kinematic Analysis of 3-D Swept Shock Surfaces in Axial Flow Compressors

2000 ◽  
Vol 123 (3) ◽  
pp. 490-500 ◽  
Author(s):  
Peng Shan
Keyword(s):  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Research Field ◽  
High Loading ◽  
Kinematic Characteristic ◽  
Sweep Angle ◽  
Quantitative Classification ◽  
Axial Flow Compressors ◽  
Blade Leading Edge

This paper is part II of a comprehensive study on the blade leading edge sweep/bend of supersonic and transonic axial compressors. The paper explores and analyzes the kinematic characteristic variables of three-dimensional (3-D) swept shock surfaces. In the research field studying the sweep aerodynamics of axial flow compressors and fans, many types of high loading swept blades are under intensive study. So, in both direct and inverse design methods and experimental validations, an accurate grasp of the sweep characteristic of the blade’s 3-D swept shock surface becomes of more concern than before. Associated with relevant blading variables, this paper studies the forward and zero and backward sweeps of shock surfaces, defines and resolves every kind of useful sweep angle, obtains dimensionless sweep similarity factors, suggests a kind of method for the quantitative classification of 3-D shock structures, and proposes the principle of 3-D shock structure measurements. Two rotor blade leading edge shock surfaces from two high loading single stage fans are analyzed and contrasted. This study is the foundation of the kinematic design of swept shock surfaces.

Vortex Generation in Two Intracranial Aneurysms

2014 ◽  
Author(s):  
Hafez Asgharzadeh ◽  
Iman Borazjani ◽  
Jianping Xiang ◽  
Hui Meng
Keyword(s):  
Immersed Boundary Method ◽  
Time Scale ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Immersed Boundary ◽  
Parent Artery ◽  
Aneurysm Neck ◽  
Vortex Formation Time ◽  
Previous Hypothesis ◽  
Aneurysm Shape

Three-dimensional numerical simulations, using the sharp-interface immersed boundary method, are carried out to investigate the effect of aneurysm shape on the hemodynamics of intracranial aneurysm. In our previous work [1] only a single geometry of an aneurysm was tested, but here two three-dimensional geometries are tested by reconstruction from three-dimensional rotational angiography of a human subject [2]. The results support our previous hypothesis [1], i.e., when the vortex formation time scale at the parent artery is smaller than the transportation time scale across the aneurysm neck, the flow aneurysm dome is dominated by a dynamic, unsteady vortex formation.

scholarly journals Three-dimensional vortex wake structure of flapping wings in hovering flight

2014 ◽  
Vol 11 (91) ◽  
pp. 20130984 ◽  
Author(s):  
Bo Cheng ◽  
Jesse Roll ◽  
Yun Liu ◽  
Daniel R. Troolin ◽  
Xinyan Deng
Keyword(s):  
Experimental Studies ◽  
Three Dimensional ◽  
Leading Edge ◽  
Ring Structure ◽  
Tip Vortex ◽  
Flapping Wings ◽  
Vortex Wake ◽  
Wake Structure ◽  
Edge Vortex ◽  
Vorticity Transport

Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity.

scholarly journals Dynamic Stall Characteristics of Pitching Swept Finite-Aspect-Ratio Wings

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 457
Author(s):  
Al Habib Ullah ◽  
Kristopher L. Tomek ◽  
Charles Fabijanic ◽  
Jordi Estevadeordal
Keyword(s):  
Aspect Ratio ◽  
Separation Bubble ◽  
Leading Edge ◽  
Dynamic Stall ◽  
Trailing Edge ◽  
Sweep Angle ◽  
Pitching Motion ◽  
Naca0012 Airfoil ◽  
Phase Average ◽  
Reduced Frequency

An experimental investigation regarding the dynamic stall of various swept wing models with pitching motion was performed to analyze the effect of sweep on the dynamic stall. The experiments were performed on a wing with a NACA0012 airfoil section with an aspect ratio of AR = 4. The experimental study was conducted for chord-based Reynolds number Rec =2×105 and freestream Mach number Ma=0.1. First, a ‘particle image velocimetry’ (PIV) experiment was performed on the wing with three sweep angles, Λ=0o, 15o, and 30o, to obtain the flow structure at several wing spans. The results obtained at a reduced frequency showed that a laminar separation bubble forms at the leading edge of the wing during upward motion. As the upward pitching motion continues, a separation burst occurs and shifts towards the wing trailing edge. As the wing starts to pitch downward, the growing dynamic stall vortex (DSV) vortex sheds from the wing’s trailing edge. With the increasing sweep angle of the wing, the stall angle is delayed during the dynamic motion of the wing, and the presence of DSV shifts toward the wingtip. During the second stage, a ‘turbo pressure-sensitive paint’ (PSP) technique was deployed to obtain the phase average of the surface pressure patterns of the DSV at a reduced frequency, k=0.1. The phase average of pressure shows a distinct pressure map for two sweep angles, Λ=0o, 30o, and demonstrates a similar trend to that presented in the published computational studies and the experimental data obtained from the current PIV campaign.

scholarly journals Three-Dimensional Radiative Flow of Hybrid Nanofluid Past a Shrinking Plate with Suction

2021 ◽  
Vol 85 (1) ◽  
pp. 54-70
Author(s):  
Nur Syahirah Wahid ◽  
Norihan Md Arifin ◽  
Najiyah Safwa Khashi’ie ◽  
Rusya Iryanti Yahaya ◽  
Ioan Pop ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Boundary Layer Separation ◽  
Hybrid Nanofluid ◽  
Volumetric Concentration ◽  
Similarity Transformations ◽  
The Stability ◽  
Energy Equations ◽  
Shrinking Surface

Hybrid nanofluid has been widely used in various heat transfer applications especially as the heat exchanger due to the great thermal conductivity compared to the conventional fluid. However, numerous investigations should still be carried out to properly understand its properties. Hence, in this study, a three-dimensional radiative flow of hybrid Cu-Al2O3/water nanofluid past a permeable shrinking plate is numerically analyzed. The boundary layer including the energy equations are reduced to a system of ordinary differential equations using the similarity transformations and are then solved numerically by using the bvp4c solver in MATLAB. The application of suction through the permeable plate is necessary in aiding the fluid motion past the shrinking surface. Dual solutions are also observable, hence the stability analysis is conducted to mathematically validate the real solution. The enhancement of copper volumetric concentration in the hybrid nanofluid is capable in decelerating the boundary layer separation.

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