Understanding and controlling vorticity transport in unsteady, separated flows

Akkala, James

doi:10.17077/etd.8t9jvlnt

Cited by 3 publications

(9 citation statements)

References 127 publications

(267 reference statements)

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“…With the following independent variables: h 0 as the motion amplitude in meters, f as the motion frequency in Hertz, and t as the time in seconds. Note that, the motion prescribed in Akkala [1] di↵ers by a factor of -1, where the plate motion moves downward initially instead of upward as seen in the simulations. To compensate for the di↵erence, the simulation results were adjusted by shifting the associated phase by 180 , resulting in the simulation data being presented in a consistent manner with the experimental data.…”

Section: Airfoil Kinematicsmentioning

confidence: 77%

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Numerical investigation of a plunging airfoil

Janechek¹

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The goal of this thesis is to investigate vortex dynamics of a plunging airfoil by studying the vorticity transport mechanisms of two-dimensional simulations. Direct numerical simulations were implemented in an e↵ort to provide detailed flow fields that are di cult to capture with experimental methods. The simulations were used to study a simplified flat airfoil in a freestream that was subject to pure plunging motion. Due to computational limits, it was not practical to simulate in three-dimensions and the results are limited to two-dimensions. Quantitative and qualitative analyses were used the validate the two-dimensional simulations and gain insight into the e↵ects of eliminating three-dimensional physics in a nominally two-dimensional flow. Additionally, a parametric study was conducted to analyze the e↵ects of Reynolds and Strouhal numbers on the transport of vorticity. iii

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Section: Airfoil Kinematicsmentioning

confidence: 77%

“…The work conducted by Akkala [1] was used for validation and also formed the basis for defining the airfoil dimensions used in the simulations. The experimental airfoil consisted of a flat plate with rounded leading and trailing edges.…”

Section: Domain Definitionmentioning

confidence: 99%

Numerical investigation of a plunging airfoil

Janechek¹

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“…Using the complex functions to represent the oscillations instead of sine function leads to ℎ̇= 0.122 5 For better comparison, the results for the variation of with phase from the simulation, theory and the experiment [246] are compared in Figure (4-32). It shows that the results from the SPM simulation are very close to the experimental outcomes and the predictions of Theodorsen theory.…”

Section: Investigation Of a Plunging Airfoilmentioning

confidence: 99%

“…Moreover, as shown by Eslam Panah et al [241] using a nominally 2D flat plate, the three dimensional vorticity fluxes are less important in comparison with the vorticity diffusion from the surface. Therefore, the 3D effects on a similar flat plate used in this research has a minimal effect in the flow characteristics.Instead, the transport of LEV and secondary vorticity control the LEV's stability.The simulations are set up so that the results could be compared with Akkala[246] who studied an airfoil similar toFigure (4-28)with the chord length of = 76.2 and a thickness of = 3.175 . In this 2D simulation we ignore the effect of span size of = 304.8 .…”

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confidence: 99%

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A parallelized diffuse interface solver with applications to meso scale simulation of suspensions

Mohaghegh¹

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A vorticity-based criterion to characterise leading edge dynamic stall onset

2022

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We propose a more conservative, physically-intuitive criterion, namely, the boundary enstrophy flux ( $BEF$ ), to characterise leading-edge-type dynamic stall onset in incompressible flows. Our results are based on wall-resolved large-eddy simulations of pitching aerofoils, with fine spatial and temporal resolution around stall onset. We observe that $|BEF|$ reaches a maximum within the stall onset regime identified. By decomposing the contribution to $BEF$ from the flow field, we find that the dominant contribution arises from the laminar leading edge region, due to the combined effect of large clockwise vorticity and favourable pressure gradient. A relatively small contribution originates from the transitional/turbulent laminar separation bubble (LSB) region, due to LSB-induced counter-clockwise vorticity and adverse pressure gradient. This results in $BEF$ being nearly independent of the integration length as long as the region very close to the leading edge is included. This characteristic of $BEF$ yields a major advantage in that the effect of partial or complete inclusion of the noisy LSB region can be filtered out, without changing the $BEF$ peak location in time significantly. Next, we analytically relate $BEF$ to the net wall shear and show that its critical value ( $=\max (|BEF|)$ ) corresponds to the instant of maximum net shear prevailing at the wall. Finally, we have also compared $BEF$ with the leading edge suction parameter ( $LESP$ ) (Ramesh et al., J. Fluid Mech., vol. 751, 2014, pp. 500–538) and find that the former reaches its maximum value between $0.3^{\circ }$ and $0.8^{\circ }$ of rotation earlier.

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Understanding and controlling vorticity transport in unsteady, separated flows

Cited by 3 publications

References 127 publications

Numerical investigation of a plunging airfoil

Numerical investigation of a plunging airfoil

A parallelized diffuse interface solver with applications to meso scale simulation of suspensions

A vorticity-based criterion to characterise leading edge dynamic stall onset

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