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Entrainment mechanism of turbulent synthetic jet flow

Published online by Cambridge University Press:  06 March 2023

Congyi Xu Open the ORCID record for Congyi Xu [Opens in a new window] ,
Yanguang Long Open the ORCID record for Yanguang Long [Opens in a new window]  and
Jinjun Wang Open the ORCID record for Jinjun Wang [Opens in a new window]
Congyi Xu
Affiliation:
Fluid Mechanics Key Laboratory of Education Ministry, Beihang University, Beijing 100191, PR China
Yanguang Long
Affiliation:
Fluid Mechanics Key Laboratory of Education Ministry, Beihang University, Beijing 100191, PR China
Jinjun Wang*
Affiliation:
Fluid Mechanics Key Laboratory of Education Ministry, Beihang University, Beijing 100191, PR China
*
†Email address for correspondence: jjwang@buaa.edu.cn
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Abstract

Synthetic jets have received extensive attention due to their superior mixing property. However, its mechanisms have not been investigated from the perspective of the turbulent/non-turbulent interface (TNTI). To shed new light on this issue, the entrainment and TNTI properties of a synthetic jet are experimentally investigated and compared with a continuous jet at $Re_j = 3150$. The fuzzy clustering method is applied to select an appropriate vorticity threshold to detect the TNTI. Statistically, it is revealed that the entrainment coefficients of the two jets significantly differ in the near field, while they become almost identical in the far field. Instead of the vortex ring, the ‘breakdown of the vortex ring’ enhances the entrainment in the present synthetic jet. Instantaneously, the TNTI more violently fluctuates in the near field of the synthetic jet, which leads to a larger fluctuation in the TNTI radial position, a higher fractal dimension and enhanced local entrainment. Moreover, the transition of the probability density function of the TNTI orientation from the unimodal distribution in the near field to the bimodal distribution in the far field is found in both jets. The multi-scale analysis reveals a new mechanism for the bimodal distribution caused by the TNTI-thickness-scale structures.

JFM classification

Wakes/Jets: Jets Mixing: Turbulent mixing Flow Control: Mixing enhancement

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JFM Papers
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Journal of Fluid Mechanics , Volume 958 , 10 March 2023 , A31
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© The Author(s), 2023. Published by Cambridge University Press

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