A." Sagara

H. Hashizume

M. Takahashi

S. "Satake

"Satake,  S.

Hashizume,  H.

Takahashi,  M.

Sagara,  A."

NIFS-Repository (National Institute for Fusion Science)

distribution shows the inverse for the vortex in fluid. At a=1, the sign of vortex of secondary vortex and primaryvortex are negative. Furthermore, the potential distributiondisappears at the low electrical conductivity.§ 8. Study on Thermo-Fluid Behavior ofTurbulent MHO Flows in a LiquidBlanketSatake, S. (Tokyo University of Science),Hashizume, H. (Tohoku University),Takahashi, M. (Tokyo Institute of Technology),Sagara, A. (National Institute for Fusion Science)1. Objectives21(0 dq = [2_u_z dzdy y==o( 1 )! I .:1----,----,-,12342 011.51.00.50.00t+Figure 2 Time developing of the gradient of thevelocity to the z direction-100-200-300-400-500-600-700 a ••Ii =0. 0l(wall=8)-800 - a woil =100 (wall=8)- a waI1 =O.01(wall=1/58)-900 ... a WOl1 ! =100 (wall=1/58)Figure I Vortex and potential distributions at t*=4 anda = 100: Upper shows the vortex and lower for thepotential-0.5The equation 1 shows the gradient of the velocity to thez direction at the wall. The equation is integrated for the halfregion from the wall owing to the symmetry. The value forthe time developing is shown in Fig. 2. Although thedistribution is the same and closes to the initial state, thedifference is remarkable from the first twin vortex collide atthe wall to the second one. In particular, at the largeconductivity, the difference in case of thicker wall becomeslarge. Therefore, the flow state is not affected by thedifference of the conductivity. Although the differenceappears near wall region, the current becomes large for thethicker wall. That is, the reduction of wall shear at the wall isnecessary to design for the reactor with conduction wall. Asfor turbulent flows, many twin vortexes must be existed nearthe wall. The effect of the wall conductivity must not benegligible. Therefore, we will perform the 3D turbulentMHD flow calculation in the future.1. O...--r--.,.....,........,.,.,.,...-----..........0.5In the region of transition Reynolds numbers, theincrease or decrease of friction coefficients of the coolantlike a Molten Salt having a low magnetic conductivity isexpected: a transition Hartmann number behavior. Thisbehavior also may lead the deterioration of heat transfer.Therefore, the thermo-fluid design of blanket under themagnetic filed fluctuation is very important. Since themagnetic field is strongly influenced by mean velocity whenthe magnetic field applies perpendicular to the flow direction,it is necessary to investigate the turbulent MHD flowbehaviors for each direction of the applied magnetic fieldnormal to the main flow one. Furthermore, in case ofconsidering the wall with various electrical conductivitiesthe flow characteristics of the coolant could befrom the usual turbulent non-MHD flows. In this sense, thenumerical simulation is very convenient to evaluate the flowchanges due to the change of physical properties of the wallmaterials or the direction of applied magnetic field. In thepresent study, the numerical analysis of the well-known"Vortex Dipole" problem under a magnetic field isperformed in order to evaluate the influence of an electricalconductivity of the first wall.The two-dimensional continuity and momentumequations for fluid motion and the potential equation forelectrical field under a low magnetism Reynolds numberassumption were solved. The MHD fluid is in a channel withelectrical conductive walls. One pair of vortex with apositive or negative circulation located at the center of thechannel is introduced at first and then the vortex motion istraced by numerical simulation. The Reynolds number basedon the circulation and the viscosity is 1800. The electricalconductivities of the wall are set to 0.01, 1, and 100. Inorder to investigate the effect of wall thickness, two caseswith different thickness: 1 8 and 1/5 8 were examined.2. Numerical method and boundary condition forVortex Dipole problem3. ResultsFigure 1 shows the vortex contour that vortex pairattached at the wall with 0=100 at t*=4 and the 2-D contourfor potential distribution inside the wall at the same time.The distributions of vortex for all cases with different wallelectrical conductivities are almost the same. However, thepotential distribution inside wall with a=O.O 1 is differentfrom the fluid one and the sign of the wall potential250

Study on Thermo-Fluid Behavior of Turbulent MHD Flows in a Liquid Blanket

Study on Thermo-Fluid Behavior of Turbulent MHD Flows in a Liquid Blanket

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