Experimental investigation of the transient phase of the Lorentz force response to the time-dependent velocity at finite magnetic Reynolds number

The working principle of Lorentz force velocimetry (LFV) is based on a linear dependence between measured force and velocity. We consider a case when a violation of that linear law takes place in order to take this effect into account for LFV. The response of the Lorentz force to a time-dependent velocity of solid conducting rods is experimentally studied. Solid conductors were chosen due to the fact that at a limited length of imposed magnetic field the end effects of secondary field generation are identical both in liquid and solid conductors. Thus one can simulate clearly a distortion of the imposed magnetic field in the case of non-stationary fluid flows. The magnetic Reynolds number Re_m^τ based on advection time was of the order of unity. It is demonstrated that magnetic field advection effects lead to a Lorentz force difference in low-Re_m^τ and finite-Re_m^τ cases. The induced magnetic field measurements and experimental estimation of the eddy current density are reported. (paper)