| Rayleigh-Bénard convection(RBC) is the most typical model of thermal convection. RBC is an important mechanism of heat transfer and mass transfer in the natural and a number of engineering applications. In recent years, the RB convection problem has been widely concerned at home and abroad. At the same time, since the Toms found that long chain polymer addition can significantly reduce the flow drag,since then viscoelastic fluid with its unique drag reduction characteristics attracted various attention from home and abroad,and more and more scholars began on the deep study of it, and found it a lot different to Newtonian fluid properties, such as viscoelasticity and stress delay, reduce friction and shear thinning etc.. In view of the particularity of the viscoelastic fluid refrigerant, we conjecture whether there will be some special flow and heat transfer phenomena when viscoelastic fluid occurred RB turbulent thermal convection. Therefore, starting from this problem, this paper studies in the infinite plate viscoelastic fluid RB thermal convection by using direct numerical simulation(DNS) technology.In this paper, based on the finite difference method and combined with the Giesekus constitutive equation model, the three-dimensional numerical solution of RB thermal convection in an infinite plate is obtained. Then, the flow and heat transfer of different fluids in the RB turbulent flow in the soft turbulent zone are studied.First, based on the DNS database, through the comparison of Newton fluid and viscoelastic fluid dimensionless instantaneous velocity and temperature field evolution as a function of time, we obtain the effect of viscoelastic additives on RB turbulent thermal convection flow that initiates the delay phenomenon.Secondly, we study the effect of viscoelastic additives on the heat transfer of turbulent heat transfer in RB, and get the conclusion that the heat transfer enhancement. And then, We study the influence of different parameters(number of Rayleigh number and Wesenberg number) of viscoelastic fluid RB turbulent thermal convection from a statistical point of view, with Ra number and Wi number increased, the conclusion that heat transfer enhancement.Finally, after setting the reasonable temperature threshold, the coherent structure in the Newtonian and viscoelastic fluid RB turbulent thermal convection has been successfully extracted from the background flow, and found that the viscoelastic additives have the ability to strengthen the temperature boundary layer instability, and then promote the plume eruption, which led to the enhancement of heat transfer. |
