Using compressed gases with Prandtl numbers near 0.7, we obtained flow visualizations of turbulent Rayleigh-Bénard convection in a cylindrical sample with an aspect ratio Γ≡D/L≅10 (D is the diameter and L the height) by the shadowgraph method. Focusing on the plumes under the top plate, we found that their length had a log-normal distribution, suggesting a fragmentation process. Fragmentation e...

The unsteady flow caused by the interaction of guide vanes and runner is investigated for an axial turbine. The calculation is performed in parallel. The solution algorithm and the parallelization procedures are described. The parallelization is obtained by domain decomposition with overlapping meshes. The interaction of rotor and stator is handled by a sliding interface where downstream the no...

The Prandtl model succinctly combines the 1D stationary boundary-layer dynamics and thermodynamics of simple anabatic and katabatic flows over uniformly inclined surfaces. It assumes a balance between the along-the-slope buoyancy component and adiabatic warming/cooling, and the turbulent mixing of momentum and heat. In this study, energetics of the Prandtl model is addressed in terms of the tot...

In 1986, Yakhot and Orszag developed a dynamic renormalization group method to solve the turbulence problem. In this paper, a particular random force is added to the Navier-Stokes Equation, and then following the standard renormalization group procedure, renormalization group equations and fixed points can be obtained. Together with some perturbation methods, many important turbulent constants ...

We measured Reynolds numbers Re of turbulent Rayleigh-Bénard convection over the Rayleighnumber range 2×10 <∼ R <∼ 10 11 and Prandtl-number range 3.3 <∼ σ <∼ 29 for cylindrical samples of aspect ratio Γ = 1. For R <∼ Rc ≃ 3× 10 9 we found Re ∼ R βeff with βeff ≃ 0.46 < 1/2. Here both the σand R-dependences are quantitatively consistent with the Grossmann-Lohse (GL) prediction. For R > Rc we fou...

This is the third in a series of our study of Rayleigh-Bénard convection at large Prandtl number. Here we investigate whether stationary statistical properties of the Boussinesq system for Rayleigh-Bénard convection at large Prandtl number are related to those of the infinite Prandtl number model for convection that is formally derived from the Boussinesq system via setting the Prandtl number t...

We find that in the kinematic limit the ensemble averaged square of the curvature of magnetic field lines is exponentially amplified in time by the turbulent motions in a highly conductive plasma. At the same time, the ensemble averaged curvature vector exponentially decays to zero. Thus, independently of the initial conditions, the fluctuation field becomes very curved, and the curvature vecto...