Submitted by:
Sergey Smolentsev, Karani Gulec, Alice Ying, Neil Morley

1. Topic name:
Turbulent heat transfer in liquid free surface and closed duct flows of conducting, high Prandtl number liquids with and without a magnetic field

2. In which branch(es) of science is this relevant?
Fluid dynamics and Turbulence, magnetohydrodynamics, heat transfer, computational fluid dynamics

[Non-Fusion Example applications: Material Science (Casting), Oceanography and Environmental Science (CO2 missing sink problem), Chemistry (Mass transport and enhanced diffusivity by means of turbulence in the presence of thermal gradient)]

3. Is the research in this field primarily
(a) a computational or modeling challenge,
(b) basic or applied scientific exploration , or
(c) both.

(c) both

3. What are the unknown phenomena that require scientific investigation?
* For free surface flows, the physics of near-surface phenomena is not known yet. It is believed that turbulent near-surface heat transfer is strongly affected by surface waves. These waves, which may be very small but non-vanishing, result from the interaction between turbulent eddies and the deformable free surface. Therefore, such mechanisms as the eddy reflection by the surface and the redistribution of kinetic energy from the normal into the tangential velocity components are very important and are in need further studies.

* The influence of magnetic field on turbulent MHD flows especially for free surface flows is not well understood. The numerical, experimental and theoretical data available at present are contradictory. On the one hand, people believe that there is a suppression of turbulence and turbulent heat transfer by a strong magnetic field. On the other hand, there is a lot of data, which demonstrate that in the presence of the magnetic field, the turbulent motion still persists and even becomes more intensive. On the one hand, the MHD turbulence is often considered as two-dimensional. On the other hand, there is a clear evidence of three-dimensional behavior for some MHD turbulent flows. So, deeper understanding of MHD turbulence that is grown in (not convected into) a magnetic field is necessary.

* The effect of high heat flux in the small thermal skin due to High Prandtl number fluid is also in need of investigation. One of the characteristics of the high Prandtl number fluids is to have step changes in the thermo-physical properties when a large temperature gradient exists. These may result in vortex formation and stratification that may change the characteristics of the turbulence structure

4. Characterize the frontier of science for this topic.
* Numerical simulation. Numerical modeling based on state-of-the-art approaches such as Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES) can provide the data needed. Such investigation

* Theoretical studies. The development of adequate mathematical models for MHD turbulent flows like Reynolds-averaged Navier-Stokes / Maxwell equations or subgrid scale models for LES is extremely important, since those models are the basis for further studies.

* Experimental studies. Precise experimental techniques and instrumentation for conducting accurate measurements within very thin near-surface layers should be developed. There are two different classes of electrically conducting fluids, optically transparent liquids (aqua electrolytes, water solutions, some molten salts) and liquid metals, which require different approaches to the problem.

5. Provide one or more citations from the scientific literature (preferably not your own, and preferably not from a fusion journal) that represents the latest advances in this field.
* Rashidi M. Burst-interface interactions in free surface turbulent flows, Physics of Fluids, Vol.9, No.11, 3485 (1997)

* Golbraikh E., Chkhetiani O.G., Moiseev S.S. The role of helicity in turbulent MHD flows, Journal of Experimental and Theoretical Physics, Vol.87, No 1, 95 (1998).

* Sommeria J., Moreau R. Why, how, and when MHD turbulence becomes two-dimensional, Journal of Fluid Mechanics, 118, 507 (1982).

* Lim J., Choi H., Kim J. Control of streamwise vortices with uniform magnetic fluxes, Physics of Fluids, Vol.10, No 8, 1997 (1998).

* Shimomura Y. Large eddy simulation of magnetohydrodynamic turbulent channel flows under a uniform magnetic field, Physics of Fluids A 3, 12, 3098 (1991).

* Morthland T.E., Walker J.S. Instabilities of dynamic thermocapillary liquid layers with magnetic fields, J. Fluid Mech., Vol. 382, 87 (1999).

6. In what way does the work push the frontier of knowledge? How is this work likely to impact the advancement of science outside of fusion?
The studies are being carried out in this field
* provide data bases for developing an adequate theory of MHD turbulence that accurately predicts physical phenomena;

* develop new instrumentation for conducting thermal and hydrodynamic (magnetohydrodynamic) measurements in the near-surface region;

* develop new numerical approaches and new mathematical models for studying three- and two-dimensional MHD free surface flows in different ranges of flow parameters.

* enhance developing new theories for MHD turbulence and for free surface renewal .

These results could be used in such fields as metallurgical diffusion of impurities, crystal growth, turbulent diffusion of CO2 in oceans, and dynamo theory. It makes a significant contribution to pure science such as the physics of nonlinear phenomena, hydrodynamic stability, and turbulence.