An experimental study on the onset of centrifugal effects in turbulent rotating thermal convection

Due to its relevance to the geo- and astrophysical flows, geostrophic turbulence, involving strong Coriolis effect and intensive turbulence, is of interests in the studies of turbulent rotating Rayleigh-Bénard convection (RRBC). However, the effect of the unavoidable centrifugal force on the geostrophic turbulence is often overlooked. Even the basic issue concerning when the centrifugal effect starts to manifest itself is still unresolved. In this talk we present an experimental study of the onset of centrifugal effect (characterized by the onset Froude number Fr_c) in RRBC. The onset Froude number Fr_c was first inferred from the increased bulk temperatures measured at cell center, which was found to scale with the Rayleigh number as Fr_c ~ Ra^0.55. This behavior can be understood qualitatively by a local force balance argument, which gives out Fr_c ~ l₀/H and thus predicts that l₀/H ~ Ra^0.55. Here, l₀ is the mean free distance of the columnar vortices in RRBC. However, the directly measured PIV results of l₀ does not support this 0.55 scaling. We thereby revised the local force balance argument by introducing a correction term, and the measured results agreed well with the revised argument. These results should be useful for future theoretical studies on the centrifugal effect in RRBC.



This work was supported by the National Natural Science Foundation of China (Grants No. 12072144 and 12232010).