| Thermal convection is a mechanism of heat transfer because of bulk motion of fluids,which universally exists in atmospheric circulation and oceanic circulation.Turbulent thermal convection model is a classical hydrodynamic model which is established from various natural convection phenomenon.Previous studies of convection mostly focused on the smooth boundary condition.While,the surfaces of most substances are rough in the real convection.It is meaningful to analyze the turbulent thermal convection with rough boundaries.In this paper,we create roughness by making the surface pyramid shape with(height of the pyramid)h=3mm = l(length of a side),The Prandtl number is kept constant at 6.8.The range of Rayleigh number in this paper is 8.3×108?3.8×109.Under this experimental condition,the temperature profile and temperature variance are measured to help us understand the heat transport mechanism and temperature statistical properties.In turbulent thermal convection,we report a study of the effect of boundary layer(BL)fluctuations on the scaling properties of the mean temperature profile?(z)and temperature variance profile ?(z).Three scaling regions are found with increasing the distance z away from the bottom conducting plate.In the turbulent boundary layer region,the measured ?(z)and ?(z)are found to have universal scaling forms ?(z/?)and ?(z/?),respectively,with varying thermal BL thickness?.In the zone outside the BL region,the measured ?(z)remains the same,so we introduce a new parameter(?)(z)to describe the change of mean temperature profile.And found the log law region,in which(?)= Aln(z/H)+ B,with H being the height of the cell.Besides,we found the amplitude A changes with Ra number in the form of A(Ra)= A0Ra?.As for temperature variance out of the BL region,we found that ?(z)scales with the cell height and follow a power law?(z)?(z/H)?,with the obtained values of ? being close to-1.45,which is universal in all the Ra number from 8.3 x 108 to 3.8 ×109. |
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