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Volume 103
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Chi, C., Ou, Z., Yu, C., Han, W., & Thévenin, D. (2025). A generalized memory effect in fluid/flame dynamics due to unsteady events. Particuology, 103, 232-241. https://doi.org/10.1016/j.partic.2025.05.021
A generalized memory effect in fluid/flame dynamics due to unsteady events (Open Access)
Cheng Chi a *, Zhisong Ou b, Chunkan Yu c, Wang Han d, Dominique Thévenin a
a Laboratory of Fluid Dynamics and Technical Flows, University of Magdeburg “Otto von Guericke”, Magdeburg, D-39106, Germany
b State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, 430071, China
c Institute of Technical Thermodynamics, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany
d School of Astronautics, Beihang University, Beijing, 100191, China
10.1016/j.partic.2025.05.021
Volume 103, August 2025, Pages 232-241
Received 15 March 2025, Revised 16 May 2025, Accepted 28 May 2025, Available online 6 June 2025, Version of Record 10 June 2025.
E-mail: cheng.chi@ovgu.de
Highlights

• “Memory effect” is identified and generalized, for the first time, for fluid/flame dynamics.

• The Damköhler number is found to determine the intensity of memory effect.

• One specific application of memory effect is provided, for biomimetic locomotion.


Abstract

Though being an important mechanism in systems involving unsteady fluid flows (e.g., fluids interacting with moving structures, particles in turbulent flows, turbulent flame propagation), the memory effect is usually not considered and has not attracted much attention. The present study tries to highlight the importance of this memory effect based on a variety of examples. In this manner, the three key components characterizing the memory effect can be identified in a general manner. The central mechanism controlling the memory effect is then investigated by studying the flow over a shrinking particle. It is found that the Damköhler number comparing the timescales of the unsteady (trigger) event and of the feedback on the flow directly determines the intensity of the memory effect; a smaller Damköhler number results in a more intense effect. Finally, the flow induced by a flapping wing is considered to demonstrate that the memory effect could be also beneficial for practical applications, for instance for biomimetic locomotion.

Graphical abstract
Keywords
Memory effect; Fluid-structure interaction; Turbulent flames; Unsteady flows
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