Direct numerical simulation of turbulent pipe flow controlled by MHD for drag reduction

We studied the MHD control of drag reduction in pipe flow through DNS. TheLorentz force is generated in the conductivity fluid by an array ofelectrodes and magnets fixed on the inner face of the pipe, when the voltageis applied on the electrodes. The drag is decreased numerously by changingthe amplitude and the period of the force. We studied the relation betweenthe ratio of drag reduction and the control parameters, and the physicalmechanism is discussed additionally. The MHD control possesses the optimumperiod, the maximum drag reduction is 24.2\%; The MHD control depressesthe fluctuations of the streamwise and normal velocity, but the azimuthalvelocity fluctuations grows with the increasing of the oscillatory period.