I have been looking at the location of shear flow centers for profiles for my mechanics of materials course.
I am trying to figure out how to determine the direction of the shear flow in a given beam section with a shear force which is either directed up or down (aligned with y-axis). In my lectures it has been said that 'the shear flow in the web of the beam section must always follow the same direction as the shear force'.
I have found some examples where it appears this rule does not work though:
In these 2 examples the shear flow direction in the web of the beam section is drawn in opposite direction of the shear force. I do not know why the aforementioned rule does not apply to these examples. Is this rule (shear flow direction in web must follow shear force direction) correct?
How do I determine the direction of shear flow for these 2 examples/in general?