<p>I think the overwhelming factor in grad school is a general interest and passion for said niche. While there is a wide variety of fields (hell you can split Fluid Mechanist into a series of sub-sets) there is a lot of overlap with other majors. ASE/ME both look at boundary layers, compressible and turbulent flow. ME/ChemEs will both look at porous flow and biotech. ME/EEs will look at photonics, MEMS and microfabrication.</p>
<p>As long as you major in something that gives you a good foundation you’ll have the knowledge to go into different fields. </p>
<p>The bottom line is that you NEED to have a general interest in the field.</p>