Investigation Of Heat Transfer And Dissipation Characteristic Of Vibrational Rayleigh-Bénard Convection With Rough Plates

Turbulent thermal convection widely exists in nature and engineering fields,and has been extensively studied in the past few decades.Previous studies mainly focused on enhancing heat transfer through single factors,such as using rough plates or adding horizontal vibration,but the mechanism of heat transfer enhancement under the coupling effect of the two factors needs further research.Therefore,we use the double distributed thermal lattice Boltzmann method(LBM)to conduct direct numerical calculations(DNS)of the vibrational Rayleigh-B énard(RB)convection with rough plates internal flow,and investigate the influence of different roughness heights and vibration frequency on the internal flow and heat transfer characteristics.Firstly,the computational accuracy of the double distributed thermal lattice Boltzmann method used in this article was verified.Traditional RB convection with Ra=107,Ra=108,and Ra=109 was selected to verify the accuracy of the numerical method.The calculated results of the time-averaged Nu number were well corresponded with the previous results.We introduced the physical model and specific parameters of the vibration RB convection system with rough plates and elaborated on the control equations and boundary conditions used in the convection system.And we verified the numerical accuracy and grid independence of the vibrational RB convection model with rough plates.Secondly,we investigate the influence of Ra number on the convective flow,heat transfer and dissipation characteristics of vibrational RB with rough plates is analyzed within the range of Rayleigh number 107 ≤Ra ≤109 and Prandtl number Pr=4.38.The research results show that the scale of plumes decrease with the increasing Ra number.And the speed of large-scale circulation(LSC)will increase,and the speed of the plume region will also increase.The scaling law of Re numbers with Ra number changes Re～Ra0.42 from to Re～Ra0.6.The Nu scaling law with Ra number has transformed from the traditional RB convection scaling law Nu～Ra1/3 to Nu～Ra1/2,which means the combination of rough boundary condition and horizontal vibration maybe a way to achieve the turbulence "ultimate range".The probability density distribution function(PDF)of temperature fluctuation in vibrational RB convection with rough plates obey the Gaussian distribution,and the small-scale intermittence of convection dissipation increases.The dominant contribution of dissipation from plume contribution to turbulent background contribution.The turbulent heat transfer mechanism of vibrational RB convection with rough plates has been revealed by small scale perspective.Finally,we study separately influence of the vibration frequency ω*and the roughness height h*at the internal flow,heat transfer characteristics,and dissipation characteristics of vibrational RB convection with rough plates at typical Ra=108.The results show that the high frequency horizontal vibration can destroy the recirculation zone of the roughness gap,thus reducing the sickness of thermal boundary layer and enhancing the heat transfer.The horizontal vibration accelerates the flow of fluids,which is conducive to the full mixing of cold and hot fluids.At h*=0.05,ω*=1000,the time-averaged Nu number of vibrational RB convection with rough plates increased by 206%compared to traditional RB convection,while only using rough plates increased by 23%and only adding horizontal vibration increased by 169%,indicating that the coupling effect of two factors is greater than the effects of single factor.The distribution area of strong thermal dissipation in the boundary region gradually increases,while the distribution area of weak theraml dissipation in the core region gradually decreases.However,the kinectic dissipation in the core region is not the smallest,which is related to the high mixing intensity region formed by horizontal vibration.Different vibration frequencies make the normalized Re number show different monotonicity on the roughness height h*due to the plume promotion on the large-scale circulation caused by horizontal vibration and the inhibition of the increase of roughness height on the large-scale circulation.This research provides a reference for the theoretical study of turbulent heat transfer with the coupling effect of rough plates and horizontal vibration,and also has guiding significance for practical applications in engineering.