Wavelet analysis of the flow field around an oscillating airfoil undergoing pure pitching motion at low Reynolds number

Ghamkhar, Kamran; Ebrahimi, Abbas; Shariloo, Koosha

doi:10.1063/5.0154125

Cited by 4 publications

(1 citation statement)

References 43 publications

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“…Centrifugal pumps account for over 80% of ship pumps and are used for ship ballast balance, pipeline heat exchange circulation, ship safety, fire protection, domestic water supply and drainage systems. The pumps on board ships are affected by the ocean environment, causing pitch motion, and their inner flow is subjected to additional swing forces, resulting in more turbulent flow and more intense flow excitation which induce the unsteady vibration of pump systems [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Research on the Performance Characteristics and Unsteady Flow Mechanism of a Centrifugal Pump under Pitch Motion

Yuan,

Gong,

Wang

et al. 2023

Water

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Pitch motion is the key factor affecting the performance characteristics of centrifugal pumps on board ships and exacerbates hydraulic excitation to induce the unsteady vibration of pump units. A hydraulic test platform with swing motion is established to explore the effects of pitch motion on a pump’s performance characteristics. An obvious hump zone exists in the head characteristic curve in the low-flow-rate condition due to the pitch motion. The pump head in the shut-off condition has a significant decrease due to the pitch motion, compared to the static state. The head decrease gradually increases as the maximum pitch angle increases or the pitch period shortens. Specifically, the head in the rated flow condition decreases by 6.3 % to reach a minimum at the maximum pitch angle of 20 degrees in a period of 5 s. Based on a multiple-reference coordinate system, a large eddy simulation with a shear-modified eddy viscosity model is employed to simulate inner flow characteristics under the influence of pitch motion. A distinct vortex flow appears near the blade suction surface and becomes increasingly turbulent as the pitch period shortens. The pitch motion intensifies the unsteady stretching and deformation of vortices. The periodic variations in fluid-induced pressure over time present parabolic features, and the amplitude in the frequency domain reaches its maximum value within a pitch period of 5 s.

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Section: Introductionmentioning

confidence: 99%

Research on the Performance Characteristics and Unsteady Flow Mechanism of a Centrifugal Pump under Pitch Motion

Yuan,

Gong,

Wang

et al. 2023

Water

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Flow structure and vortex dynamics of blade surface transitional flow in the near-tip region of a compressor cascade

Shi,

Mao,

et al. 2023

Physics of Fluids

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The mean flow topology and vortex dynamics of the blade surface transitional flow in the near-tip region of a C4 compressor blade were investigated using particle image velocimetry measurements with two configurations. The experiment was conducted in a compressor cascade at a chord Reynolds number of 24 000 and an incidence angle of 0°, and a laminar separation bubble was detected on the aft portion of the blade. In the half-span region of the blade, the separation is essentially two-dimensional without reattachment. The vortex dynamics are dominated by the periodic shedding of separated shear layer vortices and their interaction with the trailing edge vortices. The progressive spanwise evolution in the flow structures and vortex dynamics occur near the blade tip (70%–80% blade height), leading to an advanced, thinner separation. In contrast, the tip leakage vortex dominated region is restricted to approximately 20% of blade height from the blade tip. In this region, secondary flow effects are intensive enough to prevent laminar separation. Between the above two regions, there is a transition region (90% blade height), where the influence of the tip flow on the blade surface flow is relatively slight that merely suppresses the vortex shedding of the separated boundary layer, nor the whole shear layer. In the transition region, the velocity fluctuations are significantly reduced.

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The power-extraction regime of a figure-eight trajectory flapping-foil turbine

Zheng,

Yao,

Bai

et al. 2024

Physics of Fluids

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At specified Reynolds numbers Re=ρvc/μ=5×105, this study investigates the power-extraction regime of a flapping-foil turbine executing a figure-eight trajectory. This study thoroughly explored the impacts of trajectory shape, heave and pitch amplitudes, phase difference, and pitch axis location on the power-extraction regime of a flapping turbine. A figure-eight trajectory substantially bolsters the energy harvesting capacity, achieving a peak efficiency of up to 50%. This trajectory capitalizes on the energy generated from the drag encountered by the flapping foil, thereby marking a significant efficiency breakthrough. This could denote a considerable progression for flapping foils tailored for heave and pitch motions since the free stream can be optimally harnessed by the trajectory we have established. In scenarios where the flapping foil undergoes the same maximum effective angle of attack, a wake diffusion spectrum aligns with the Betz limit threshold. Crucially, the closeness to this efficiency frontier suggests a universal maximum effective angle of attack—a consistent law that remains valid for the conventional flapping turbine design. It implies that selections for stroke and pitch amplitudes should be methodical rather than arbitrary. In addition, the positioning of the pitch axis ought to be modified in tandem with phase difference adjustments to bolster the synchronization between heaving motions and resultant lift. The ideal phase difference is variable, contingent on pitch amplitude and pitch axis position. Even with low pitch amplitudes, fine-tuning the phase difference guarantees that the energy harvesting efficiency does not fall below 30%. Such an enhancement would significantly broaden the operational envelope and the parameter space for flapping turbines.

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Wavelet analysis of the flow field around an oscillating airfoil undergoing pure pitching motion at low Reynolds number

Cited by 4 publications

References 43 publications

Research on the Performance Characteristics and Unsteady Flow Mechanism of a Centrifugal Pump under Pitch Motion

Research on the Performance Characteristics and Unsteady Flow Mechanism of a Centrifugal Pump under Pitch Motion

Flow structure and vortex dynamics of blade surface transitional flow in the near-tip region of a compressor cascade

The power-extraction regime of a figure-eight trajectory flapping-foil turbine

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