Entry length for circular and rectangular ducts in strong magnetic fields

J. S. Walker - G. S. S. Ludford

Abstract
Estimates are presented for entry lengths in circular and rectangular constant-area ducts in the presence of strong transverse magnetic fields, together with the conditions (in terms of the Hartmann number, the interaction number, and the wall conductivity ratio) under which each estimate is valid. As the magnetic field becomes sufficiently strong for inertial effects to be neglected, the entry length becomes comparable to or smaller than the cross-sectional diameter for all rectangular ducts and for highly conducting circular ducts, but remains large for circular ducts with poor wall conductivity.