DNS and k-ε model simulation of MHD turbulent channel flows with heat transfer

In this study, the MHD pressure loss and heat transfer characteristics were investigated by means of DNS (Direct Numerical Simulation), and the evaluation of MHD turbulence model proposed by Kenjeres and Hanjalic (2000) and Smolentsev et al. (2002) were also carried out at high Reynolds number (Re) corresponding to the DNS database reported by Satake et al. (2006). At first, the numerical calculations of MHD turbulent channel flow imposed the wall-normal magnetic field were carried out by using the Kenjeres and Hanjalic (KH) model and the Smolentsev et al. (S) model at the same condition as the DNS data (Satake et al., 2006): Bulk Re=46000 and Hartmann numbers (Ha)=32.5 and 65. Compared with the DNS results, both turbulence models can reproduce the MHD pressure loss trend with increase of Ha. However, both models underestimated the turbulent kinetic energy, and the prediction accuracy was getting worse with increase of Ha. Compared with the KH model and the S model, the KH model has a little advantage in the prediction accuracy and this result conforms close to a priori test in MHD source terms in k- and ε-equation. To improve the prediction accuracy of the k-ε turbulent model, some modification of eddy viscosity would be required. Next, DNS of 2D-fully developed turbulent channel flows imposed wall-normal magnetic field were conducted to investigate heat transfer characteristics. In the computations, thermal properties of the KOH solution (Pr number is 5.2 at 40 C.) were used because the KOH solution instead of FLiBe was used in the JUPITER-2 experiment. Turbulent Reynolds number was kept on 150 and Ha was changed from 0 to 16. The continuity equation, the momentum equations with the electric field described using the electrical potential approach at low magnetic Reynolds number and the energy equation were solved by a hybrid Fourier spectral and the second order central differencing method (Yamamoto et al., 2002). As the results, the velocity profile completely changed from turbulent flow to the laminar one in Ha=13.4. Ha=13.2 was the near critical condition in this Reynolds number of the turbulent-laminar transition. (orig.)