On Substitution Principles in Ideal Magneto-Gasdynamics by Means of Lie Group Analysis

The equations governing the flow of an inviscid thermally non-conducting fluid of infinite electrical conductivity in the presence of a magnetic field and subject to no extraneous forces are considered within the framework of Lie group analysis. It is shown how to recover and extend some results, known in literature as substitution principles, by conveniently requiring the invariance of the basic governing equations under a one-parameter Lie group of point transformations. Moreover, a new substitution principle for the equations ruling the plane motion of a fluid with adiabatic index Γ = 2 subjected to a transverse magnetic field is given. Some applications of the results are also given.