CXLII. Experiments on magneto-hydrodynamic channel flow

Summary Experiments are described in which measurements of pressure gradient were taken during the flow of mercury in a rectangular channel of 15 : 1 aspect ratio, in the presence of a transverse magnetic field. It was possible to suppress turbulence even at the highest obtainable Reynolds Number (R=105). For high values of R, the friction coefficient C f appears to be a function of M/R and β. It is suggested that when R is large enough C f might be a function of the single group M/Rβ 1/2 . This is comparable with the simple relationship proposed by Hartmann and Lazarus (1937). Lundquist (1952) has suggested that the transition from laminar to turbulent flow occurs at a fixed value of R/M, and that β does not enter into this criterion. The experiments suggest that the critical condition for the turbulent to laminar transition is R/M ≈ 900, although since only one liquid was used, it was not possible to determine the influence of β.