Measurements Of The Large-Scale Circulation In Turbulent Thermal Convection With Different Tilt Angle And Prandtl Numbers

Large-scale circulation(LSC)exists widely in nature,such as atmospheric circulation and ocean circulation.In this paper,LSC in a tilted Rayleigh-Bénard turbulent thermal convection system are studied.The experimental device is a cylindrical convection cell with an aspect ratio Γ = 1.The fluid medium in this experiment is glycerol solution of different concentrations,and Prandtl number of the experiment is controlled by mixing solutions of different concentrations.The central temperature of the system is kept constant at 30℃,Ra number is controlled by temperature difference.The measurements are carried out over a wide range of tilt angles.In Rayleigh-Bénard turbulent thermal convection system,the motion of LSC plane includes rotation motion and slopping motion.In order to explore the LSC,this experiment is studied by measuring the temperature on the sidewall of the system midplane.Sine and cosine function models can be used by the measured temperatures,the results can help us obtain the dynamic parameters of LSC,including rotation angle and slosh angle.The transition process from turbulent motion to laminar motion can be found by analyzing the temperature time series of the mid-plane as well as the change between the rotation angle and the slob angle of the LSC over time.In addition,we also analyze the rotation angle of the LSC,and it shows gaussian distribution under different angle rotation of the LSC.However,with the increase of angle rotation,standard deviation of angle probability density distribution becomes smaller.Which means that the smaller of scope of the LSC rotation,the more concentrated near the maximum probability of angle rotation.While studying the slopping angle,finding that the LSC moves back and forth symmetrically on the rotating plane when the dip angle is 0°.However,with the increase of the dip Angle,the LSC wobbles only on one side of the rotating surface.Then,the research of the influence of Pr number on LSC helps us found that owing to the Pr number increase,the rotation range of LSC decrease.That is,the rotation angle of the rotation motion was more close to the maximum probability rotation angle,while the slob motion of LSC was not affected by Pr number.After analyzing the heat transfer of RBC system,it was found that the heat transfer of Nu was not significantly affected,while the tilt angle would affect the heat transfer of the system.Therefore,Nu number tend to go down firstly when it at a small tilt angle,and then it’s going to go up as the tilt angle goes up.And it will go down once it arrive the peak.