Separation control based on turbulence transition around a two-dimensional hump at different Reynolds numbers

Yakeno, Aiko; Kawai, Soshi; Nonomura, Taku; Fujii, Kozo

doi:10.1016/j.ijheatfluidflow.2015.07.014

Cited by 22 publications

(10 citation statements)

References 34 publications

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“…The first was why the use of burst waves improved flow control authority, while the second was why F + = 6.0 showed a better flow control than F + = 1.0 in both our experiments and simulations. Numbers of iLES simulations were conducted under the project of application software development of the K supercomputer in Japan [40][41][42][43][44]. Simulations with different parameters (airfoil geometry, angle of attack, Reynolds number, D c , F + , etc.)…”

Section: Use Of Burst Waves: Observations In Our Early Studymentioning

confidence: 99%

Three Flow Features behind the Flow Control Authority of DBD Plasma Actuator: Result of High-Fidelity Simulations and the Related Experiments

Fujii

2018

Applied Sciences

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Both computational and experimental studies are conducted for understanding of the flow separation control mechanism of a DBD (dielectric barrier discharge) plasma actuator. Low speed flows over an airfoil are considered. A DBD plasma actuator is attached near the leading edge of an airfoil and the mechanism of flow control of this small device is discussed. The DBD plasma actuator, especially in burst mode, is shown to be very effective for controlling flow separation at Reynolds number of 6.3 × 10 4 , when applied to the flows at an angle of attack higher than the stall. The analysis reveals that the flow structure includes three remarkable features that provide good authority for flow separation control with the appropriate actuator parameters. With proper setting of the actuator parameters to enhance the effective flow features for the application, good flow control can be achieved. Based on the analysis, guidelines for the effective use of DBD plasma actuators are proposed. A DBD plasma actuator is also applied to the flows under cruise conditions. With the DBD plasma actuator attached, a simple airfoil turns out to show higher lift-to-drag ratio than a well-designed airfoil.

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Section: Use Of Burst Waves: Observations In Our Early Studymentioning

confidence: 99%

Three Flow Features behind the Flow Control Authority of DBD Plasma Actuator: Result of High-Fidelity Simulations and the Related Experiments

Fujii

2018

Applied Sciences

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“…The air eddies near the nozzle body could affect the cooling to the ribbon, cause periodic changes in the convective heat transfer and even the dynamic pressure on the ribbon surface. The eddy formed out of the solidification area exhibits the similar size to the ribbon ripple wavelength [1], [10], the formation mechanism of ripple on the air-side could be due to the periodic air flow eddies. When the upstream air flows in the gap approaching the liquid film, shown in Fig.10, the velocity is lower near center with regularly vibration; the amplitude of flow vibration is at least 3 m/s, which could contribute to the ripple formation from both solidification rate and air flow impact vibration.…”

Section: Eddies On the Roller Surfacementioning

confidence: 99%

“…For the ribbon produced by Yunlu here, the variation in ribbon thickness is about 2~3 μm. The air flow over the roller played a key role, like the turbulence flow around a two-dimensional hump [10] and to fluctuated cool the alloy liquid. The nozzle effect and geometry are also the important factors [11]- [12].…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of the Air Flow Effects on Amorphous Alloy Ribbon Formation

Wang

2017

MATEC Web Conf.

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During the amorphous ribbon production process, the mechanisms that cause uneven thickness and herringbone on two surfaces of the ribbon are very complicated. The high velocity rotating roller causes periodic air eddies near the surface and air flow around the contact zone. The air flow might be the major reason that causes the non-uniformity thickness and the ripples. In this paper, a two-dimension model was developed to simulate the air flow eddies and a three-dimensional simulation was performed for the air flow field around the puddle zone. Simulation results show that the higher velocity of air flow around the puddle edges is closely related to thicker ribbon rim. The continuous air eddies along the roller surface and the air flow fluctuations along the roller width are the major reasons causing non-uniform convective heat transfer during ribbon solidification. The frequency of air eddy matches well with the nominal ripple frequency along the ribbon length, and the air flow fluctuation coincides with the herringbone wavelength along the ribbon width. The influences of the air flow on cooling, ribbon thickness, and herringbone phenomena are all discussed here.

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“…Mardkari et al (2012) experimentally determined the influence of EHD actuator on the fluid flow past bluff body of cylindrical crosssection and showed total drag suppression. Yakeno, et al (2015) established two-dimensional excitation induced by plasma actuator with dielectric barrier discharge to control the separation and reattachment of flow over the hump. The reattachment is imposed by excitation control with increasing the turbulence fluctuation.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Presence of the Lorentz Force and its Direction on the Suppression of Secondary Flow in Two Different Orifices: A Numerical Study using OpenFOAM

Singh¹,

Gohil²

2019

JAFM

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The present analysis emphasized the presence of Lorentz force and its directional effect on the fluid flow and its structure in the channel with two differently shaped orifices. The flow through orifice causes the generation of the bubbles or eddies in the downstream flow. In this study, the numerical code is developed in the open source CFD tool kit OpenFOAM. The magnetohydrodynamics (MHD) principle is adopted to achieve the present objectives. Direct numerical simulation (DNS) has been carried out to predict the flow features at fixed Reynolds number of Re = 1000 and blockage ratio of 1:4 with the varying magnetic field. The magnetic field is varied in term of Hartmann number (Ha) in the direction normal to the flow of fluid. The induced Lorentz force considerably occupies the wake flow area downstream of the throat and hence suppressed down the vortices in the flow. The results obtained has the promising effect of suppressing down the vortex flow past two different orifices produced by the electromagnetic pressure gradient. The present study shows the MHD based flow can be significantly employed for the flow past orifice or any arbitrary obstacle in order to achieve the flow without wake region. The current analysis suggests the method of vortex control by producing Lorentz force using magnetic field without modification of geometry or additional use of devices into the system.

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Separation control based on turbulence transition around a two-dimensional hump at different Reynolds numbers

Cited by 22 publications

References 34 publications

Three Flow Features behind the Flow Control Authority of DBD Plasma Actuator: Result of High-Fidelity Simulations and the Related Experiments

Three Flow Features behind the Flow Control Authority of DBD Plasma Actuator: Result of High-Fidelity Simulations and the Related Experiments

Numerical Investigation of the Air Flow Effects on Amorphous Alloy Ribbon Formation

Influence of the Presence of the Lorentz Force and its Direction on the Suppression of Secondary Flow in Two Different Orifices: A Numerical Study using OpenFOAM

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