Leading-edge vortex formation and transient lift generation on a revolving wing at low Reynolds number

The mechanisms of leading-edge vortex (LEV) formation and its stable attachment to revolving wings depend highly on Reynolds number ( $\textit {Re}$ ). In this study, using numerical methods, we examined the $\textit {Re}$ dependence of LEV formation dynamics and stability on revolving wings with $\textit {Re}$ ranging from 10 to 5000. Our results show that the duration of the LEV formation period and its steady-state intensity both reduce significantly as $\textit {Re}$ decreases from 1000 to 10. Moreover, the primary mechanisms contributing to LEV stability can vary at different $\textit {Re}$ levels. At $\textit {Re} <200$ , the LEV stability is mainly driven by viscous diffusion. At $200<\textit {Re} <1000$ , the LEV is maintained by two distinct vortex-tilting-based mechanisms, i.e. the planetary vorticity tilting and the radial–tangential vorticity balance. At $\textit {Re}>1000$ , the radial–tangential vorticity balance becomes the primary contributor to LEV stability, in addition to secondary contributions from tip-ward vorticity convection, vortex compression and planetary vorticity tilting. It is further shown that the regions of tip-ward vorticity convection and tip-ward pressure gradient almost overlap at high $\textit {Re}$ . In addition, the contribution of planetary vorticity tilting in LEV stability is $\textit {Re}$ -independent. This work provides novel insights into the various mechanisms, in particular those of vortex tilting, in driving the LEV formation and stability on low- $\textit {Re}$ revolving wings.

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A cyber-physical fluid dynamics investigation of the impact of fluid structure interaction on low-Reynolds number wings and leading edge vortex evolution

35th AIAA Applied Aerodynamics Conference ◽

10.2514/6.2017-4360 ◽

2017 ◽

Cited By ~ 2

Author(s):

Raghu B. Gowda ◽

Mohamad Irfan Anwar ◽

Field H. Manar ◽

Bradford G. Olson ◽

Kristofer Tite ◽

...

Keyword(s):

Fluid Dynamics ◽

Reynolds Number ◽

Low Reynolds Number ◽

Fluid Structure Interaction ◽

Leading Edge ◽

Fluid Structure ◽

Leading Edge Vortex ◽

Structure Interaction ◽

Edge Vortex ◽

The Impact

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Surging and plunging oscillations of an airfoil at low Reynolds number

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.674 ◽

2014 ◽

Vol 763 ◽

pp. 237-253 ◽

Cited By ~ 46

Author(s):

Jeesoon Choi ◽

Tim Colonius ◽

David R. Williams

Keyword(s):

Reynolds Number ◽

Low Reynolds Number ◽

Leading Edge ◽

Unsteady Motion ◽

Flow Structures ◽

Wake Instability ◽

Edge Vortex ◽

Vortex Shedding Frequency ◽

The Mean ◽

Low Reynolds

AbstractWe investigate the forces and unsteady flow structures associated with harmonic oscillations of an airfoil in the streamwise (surging) and transverse (plunging) directions in two-dimensional simulations at low Reynolds number. For the surging case, we show that there are specific frequencies where the wake instability synchronizes with the unsteady motion of the airfoil, leading to significant changes in the mean forces. Resonant behaviour of the time-averaged forces is observed near the vortex shedding frequency and its subharmonic; the behaviour is reminiscent of the dynamics of the generic nonlinear oscillator known as the Arnol’d tongue or the resonance horn. Below the wake instability frequency, there are two regimes where the fluctuating forces are amplified and attenuated, respectively. A detailed study of the flow structures associated with leading-edge vortex (LEV) growth and detachment are used to relate this behaviour with the LEV acting either in phase with the quasi-steady component of the forces for the amplification case, or out of phase for the attenuation case. Comparisons with wind tunnel measurements show that phenomenologically similar dynamics occur at higher Reynolds number. Finally, we show that qualitatively similar phenomena occur during both surging and plunging.

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Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

Journal of Turbomachinery ◽

10.1115/1.2841351 ◽

1999 ◽

Vol 121 (3) ◽

pp. 558-568 ◽

Cited By ~ 58

Author(s):

M. B. Kang ◽

A. Kohli ◽

K. A. Thole

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Leading Edge ◽

Reynolds Numbers ◽

Secondary Flows ◽

Edge Region ◽

Leading Edge Vortex ◽

Stator Vane ◽

Edge Vortex ◽

The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

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