Transitions in rotating convection (DNS)
Aim: To investigate transitions between turbulent states by exploring the dynamics of inertial and buoyant particles in rotating Rayleigh-Bénard convection
Turbulent flow is an important phenomenon in nature and technology. There is increasing evidence that different states of turbulence exist and that there are sharp transition between these states. Because of these transitions, extrapolation from lab-scale experiments to industrial or geophysical flows is difficult. It is important to investigate whether these different states of turbulence indeed exist and how they are triggered. Of particular interest is the transition to ‘ultimate turbulence’, in which the transfer properties, such as heat transfer in thermal convection, are optimal.
In this project the focus is on Rayleigh-Bénard turbulence, which is generated by heating a closed box from below and cooling it from above as shown in figure 1. The system is characterized by the Rayleigh number, which is a dimensionless number associated with the heat transfer. Since the system is closed, the interplay between boundary layers and the bulk is of importance.
Figure 1: Geometry of the Rayleigh-Bénard system, including the hot bottom plate and the cold top plate. One of the dimensionless control parameters is the Rayleigh number: Ra = gβΔL³/νκ, with Δ the temperature difference between the top and bottom plate, g the gravitational acceleration and β, ν and κ the thermal expansion coefficient, kinetmatic viscosity and the thermal diffusivity, respectively. (The figure is taken from http://www.cpr.cuhk.edu.hk/en/press_detail.php?id=85)
In figure 2 a snapshot of the temperature field in such a Rayleigh-Bénard system is shown. This temperature field is the result of 3D numerical simulations performed by Stevens et al. In the temperature field fine structures of the turbulent flow are revealed.
Figure 2: Numerical result for Rayleigh-Bénard convection. A cut through the temperature field of the highest Rayleigh-number simulation is shown (Ra = 2 × 1012 ), revealing very fine structures of the turbulent flow and the sepration of length scales. This result is presented by Stevens et al. in Journal of Fluid Mechanics (2011).
In this research point particles will be implemented in the Rayleigh-Bénard system. The effect of the particle properties on the thermal convection, which is the transfer of heat by fluid movement, and the transition between turbulent states is explored. In particular, the interest is on preferential accumulation of particles in plumes and/or vortices, feedback on the flow and the possible modification of the interaction between bulk and boundary layer. Both a cylindrical setup and a box setup are used with either laterally bounded or lateral periodic boundary conditions. This numerical research is done in parallel with Rayleigh-Bénard experiments performed in the WDY labs. One of the goals is to close the gap between these experiments and the numerics, by pushing the simulations to higher Rayleigh number regimes.
Kim Alards, Hadi Rajaei, Rudie Kunnen, Federico Toschi, Herman Clercx
Pranav Joshi (former postdoc)