PROGRAM

Guowei He Institute of Mechanics of CAS

Bio: Dr. Guowei He is a professor and the academic director of the Institute of Mechanics, the Chinese Academy of Sciences. He is an elected Academician of the Chinese Academy of Sciences and a fellow of the American Physical Society. He is the associated editor of the APS journal “Phys Rev. Fluids”. His research interests include turbulence statistical theory and computational modeling, large eddy simulation of turbulence-generated noise and machine learning.

Space-time energy spectra for turbulence shear flows.

A space-time (frequency-wavenumber) energy spectrum describes the energy distribution of velocity fluctuations over a broad range of spatial and temporal length scales. It not only characterizes dynamic coupling between spatial and temporal scales in turbulent flows but also plays a key role in turbulence-generated noise. In this lecture, our recent work is introduced on space-time energy spectra and its application to turbulence-generated noise. The Taylor, Kraichnan-Tennekes, and elliptic approximation (EA) models are re-examined in terms of the picture of turbulent passage, which is proposed by Taylor’s frozen-flow hypothesis and the Kraichnan-Tennekes random sweeping hypothesis; The composite resolvent operators are developed for space-time energy spectra; the large-eddy simulation for frequency spectra is used to study the noise radiated by turbulent flows around an axisymmetric body of revolution.

Reference:

1.   He, Jin and Yang, Annu. Rev. Fluid Mech. 49 51-70. 2017

2.   Wu and He, Phys. Rev. Fluids Vol. 6 100504 2021 (APS invited talk)

Evgeny A. Kuznetsov P.N. Lebedev Physical Institute of RAS

Bio: Evgeny A. Kuznetsov is currently a Principle Research Fellow at Lebedev Physical Institute of RAS and Landau Institute for Theoretical Physics. He graduated from Novosibirsk State University in 1969 and received PhD from the Institute for Nuclear Physics in 1973. In 1981, he obtained the Doctor of Sciences degree at Space Research Institute. Kuznetsov is an Academician of RAS since 2016. His research interests include developed turbulence in plasma physics, hydrodynamics, magnetohydrodynamics, and stability problems of nonlinear waves and solitons.

Folding in fluids.

The formation of the coherent vortical structures in the form of thin pancakes for three-dimensional flows is studied at the high Reynolds regime when, in the leading order, the development of such structures can be described within the Euler equations for ideal incompressible fluids. Numerically and analytically on the base of the vortex line representation [1, 2] we show that compression of such structures and respectively increase of their amplitudes are possible due to the compressibility of the vorticity ω in the 3D case [3]. It is demonstrated that this growth has an exponential behavior and can be considered as folding (analog of breaking) for the divergence-free fields of vorticity. At high amplitudes this process in 3D has a self-similar behavior connected the maximal vorticity and the pancake width by the relation of the universal type [4]: ω_max ∝ l ^{−2/3 .}

[1] E.A. Kuznetsov, V.P. Ruban, Hamiltonian dynamics of vortex lines for systems of the hydrodynamic type, Pis’ma ZhETF , 76, 1015 (1998) [JETP Letters, 67, 1076-1081 (1998)].

[2] E.A. Kuznetsov, Vortex line representation for flows of ideal and viscous fluids , Pis’ma v ZHETF, 76, 406-410 (2002) [JETP Letters, 76, 346-350 (2002)].

[3] D.S. Agafontsev, E.A. Kuznetsov, A.A. Mailybaev, and E.V. Sereshchenko, Compressible vortical structures and their role in the hydrodynamical turbulence onset, UFN 192, 205-225 (2022) [Physics Uspekhi, 65 189 - 208 (2022)].

[4] D.S. Agafontsev, E.A. Kuznetsov and A.A. Mailybaev, Development of high vorticity structures and geometrical properties of the vortex line representation, Phys. Fluids 30, 095104-13 (2018); Stability of tangential discontinuity for the vortex pancakes, Pisma ZHETF, 114, 67-71 (2021) [JETP Letters, 2021, 114, 71–75 (2021)]

 The meeting will be held in the form of a webinar on the Zoom platform.

Pre-registration for the event is not required.

Link to the conference:

https://us06web.zoom.us/j/88459579267?pwd=TzliOGpReDkvSG56YVk3VTFPQ0tPQT09

Meeting ID : 884 5957 9267

Passcode：987654