Heat transfer and plume statistics in turbulent thermal convection with sparse fractal roughness  

作　　者：Guang-chun Xu Qi Wang Zhen-hua Wan De-jun Sun 

机构地区：[1]Department of Modern Mechanics,University of Science and Technology of China,Hefei 230027,China

出　　处：《Journal of Hydrodynamics》2021年第5期1065-1077,共13页水动力学研究与进展B辑（英文版）

基　　金：Projects supported by the National Natural Science Foundation of China(Grant Nos.11772323,91952103 and 11621202).

摘　　要：Rough-surface Rayleigh-Benard convection is investigated using direct numerical simulations in two-dimensional convection cells with aspect ratioГ=2.Three types of fractal roughness elements,which are marked as nl,n2 and n3,are constructed based on the Koch curve and sparsely mounted on both the plates,where n denotes the level of the roughness.The considered Rayleigh numbers Ra range from 10^(7)to 10^(11)with Prandtl number Pr=1.Two regimes are identified for cases nl,n2.In Regime I,the scaling exponentsβin the effective Nusselt number Nu vs Ra scaling Nu~Ra^(β)reach up to about 0.4.However,when Ra is larger than a critical value Ra_(c),the flow enters RegimeⅡ,with p saturating back to a value close to the smooth-wall case(0.3).Rac is found to increase with increasing n,and for case n3,only Regime I is identified in the studied Ra range.The extension of Regime I in case n3 is due to the fact that at high Ra,the smallest roughness elements can play a role to disrupt the thermal boundary layers.The thermal dissipation rate is studied and it is found that the increasedβin Regime I is related with enhanced thermal dissipation rate in the bulk.An interesting finding is that no clear convection roll structures can be identified for the rough cases,which is different from the smooth case where well-organized convection rolls can be found.This difference is further quantified by the detailed analysis of the plume statistics,and it is found that the horizontal profiles of plume density and velocity are relatively flattened due to the absence of clear convection rolls.

关 键 词：Thermal convection Rayleigh-Benard convection rough surface Introduction 

分 类 号：O35[理学—流体力学]