Experimental measurement of spatio-temporally resolved energy dissipation rate in turbulent Rayleigh-Benard convection

Xu, Fang1,2; Zhang, Lu1,2; Xia, Ke-Qing1,2,3

2024-03-27

10.1017/jfm.2024.164

JOURNAL OF FLUID MECHANICS   影响因子和分区

0022-1120

1469-7645

We report a home-built velocity-gradient-tensor-resolved particle image velocimetry (VGTR-PIV) system which spatio-temporally resolves all components of the velocity gradient tensor. This technique is applied to the paradigmatic turbulent Rayleigh-Benard convection system in a cylindrical cell at three representative positions, i.e. centre, side and bottom regions. The VGTR-PIV system allows us to directly measure, for the first time, the spatio-temporally resolved energy dissipation rate and enstrophy in turbulent thermal convection. In the experiment, the Rayleigh number Ra varied in the range 2 x 10(8) <= Ra <= 8 x 10(9) and the Prandtl number Pr was fixed at Pr = 4.34. Compared with the fully resolved energy dissipation rate epsilon, the pseudo-dissipation provides the best estimate within 3 %, the planar (two-dimensional) surrogate has a larger relative error and the one-dimensional surrogate leads to the largest error. The power-law scalings of the time-averaged energy dissipation rate with the Rayleigh number follow (t)/(nu H-3(-4)) = 9.86 x 10(-6) Ra-1.54 +/- 0.02, (t)/(nu H-3(-4)) = 9.26 x 10(-3)Ra(1.25 +/- 0.02) and (t)/(nu H-3(-4)) = 2.70 x 10(-2)Ra(1.23 +/- 0.02) in the centre, side and bottom regions, respectively where. is dynamic viscosity and H is cell height. These scaling relations, along with our earlier measured time-averaged energy dissipation rate at the bottom wall surface (t)/(nu H-3(-4)) = 9.65 x 10(-2)Ra(1.25 +/- 0.02) (J. Fluid Mech., vol. 947, 2022, A15), provide important constraints against which theoretical models may be tested. For the centre and side locations in the convection cell, the probability density functions (p.d.f.s) of the energy dissipation rate and enstrophy both follow a stretched exponential distribution. For the bottom region, the p.d.f.s of dissipation and enstrophy exhibit a stretched exponential distribution outside the viscous boundary layer and an exponential distribution inside the viscous boundary layer. It is also found that extreme events with high dissipation are the most intermittent in the side region, whereas the bottom region is less intermittent than the cell centre.

Benard convection turbulent convection

SCI ; EI

英语

第一 ; 通讯

National Natural Science Foundation of China (NSFC)["12202174","12232010","12072144","12202173","12272161"]

Mechanics ; Physics

Mechanics ; Physics, Fluids & Plasmas

WOS:001227681800001

CAMBRIDGE UNIV PRESS

ENGINEERING

Web of Science

1.Southern Univ Sci & Technol, Ctr Complex Flows & Soft Matter Res, Shenzhen 518055, Peoples R China
2.Southern Univ Sci & Technol, Dept Mech & Aerosp Engn, Shenzhen 518055, Peoples R China
3.Southern Univ Sci & Technol, Dept Phys, Shenzhen 518055, Peoples R China

Xu, Fang,Zhang, Lu,Xia, Ke-Qing. Experimental measurement of spatio-temporally resolved energy dissipation rate in turbulent Rayleigh-Benard convection[J]. JOURNAL OF FLUID MECHANICS,2024,984.

Xu, Fang,Zhang, Lu,&Xia, Ke-Qing.(2024).Experimental measurement of spatio-temporally resolved energy dissipation rate in turbulent Rayleigh-Benard convection.JOURNAL OF FLUID MECHANICS,984.

Xu, Fang,et al."Experimental measurement of spatio-temporally resolved energy dissipation rate in turbulent Rayleigh-Benard convection".JOURNAL OF FLUID MECHANICS 984(2024).