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LARGE-SCALE SPIRAL STRUCTURES IN TURBULENT NATURAL CONVECTION BETWEEN TWO VERTICAL PLATES

Minghao Wang
Department of Engineering Mechanics, Tsinghua University Beijing, 100084, China

Song Fu
Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing, 100084, China

Guanghua Zhang
Department of Engineering Mechanics, Tsinghua University Beijing, 100084, China

Resumo

For the turbulent thermal convection between two vertical plates, it is observed that the flow can generate large-scale spiral structures. Basing on the DNS data, this type of large-scale structures is studied in spectrum space and in physical space. By FFT of fluctuant velocity and kinetic energy, it is shown that the energy-intensive scale in the flow are about 0.01 in nondimensional time scale and 1.4 in nondimensional space scale, which are in accordance with the observation of the structures described useing streamlines. Further, the instantaneous flow patterns and the time evolution of such spiral structure is illustrated in the paper. For the emergence of the spiral structures, The role of helicity in the flow is to suppress the energy cascade of turbulence, reducing the dissipation, and hence preserving the topological structure of the large-scale spiral flow for a significantly long time interval.