I had the exact same question, and searched a lot. I'm sure this article can help you a lot,

http://iopscience.iop.org/article/10.1088/0256-307X/29/10/107501/meta

Cheers

Dear Muhammad,

The same question was asked by another researcher. I answer you the same way. https://www.researchgate.net/post/Why_we_apply_magnetic_field_perpendicular_to_fluid_flow

This is not always true. The uniform magnetic field is B= Bxex + Brer of constant magnitude B = (Bx^2 + Br^2)^0.5, where ex and er are unit vectors in cylindrical coordinates. The orientation of the magnetic field can form an angle Phi with the horizontal axis (the flow direction) such that Phi = Br/Bx. We often choose Phi = 90 ° to simplify the calculation (sin Phi = 1). The direction of the magnetic field is perpendicular to the flow direction. The direction of the magnetic field is perpendicular to the flow direction. But, we can also choose Phi = 0 ° or 45 ° for example. Here is a link that shows a study on the subject for different Phi angles.

http://www.j-mst.org/On_line/admin/files/10-J2010-35_333-339-340%EB%B0%B1_.pdf With my best regards Prof. Bachir ACHOUR

please look at this link may be will be useful

http://www.trifield.com/content/about-electromagnetism/

regards