Optimal linear perturbations in Hartmann channel flow: the influence of walls and magnetic damping

S. Dong¹ - D. Krasnov² - T. Boeck²

¹ Department of Power Engineering, North China Electric Power University, 071003 Baoding, China
² Institute of Thermodynamics and Fluid Mechanics, Ilmenau University of Technology, P.O.Box 100565, 98684 Ilmenau,Germany

Abstract
The transient amplification of optimal linear perturbations in Hartmann channel flow is studied at low and moderate Hartmann numbers. These perturbations are streamwise-independent vortices. They develop into streaks, which are important for subcritical transition to turbulence. The influence of the opposite channel wall is examined by comparing antisymmetric and symmetric perturbations. Differences in energy amplification between these two types of perturbations decrease rapidly with the Hartmann number. Moreover, the energy amplification in Hartmann flow is close to that in an asymptotic suction boundary layer, i.e. the magnetic damping of perturbations has only a weak effect on transient growth. Tables 1, Figs 9, Refs 15.