What are the standard practices for hyphenating/spelling scientific words
This depends upon what's being written. For a university thesis, for instance, you should follow the guidelines of your particular institution: if they recommend a particular style manual, such as the Chicago Manual of Style or the [ACS Style Guide], then you should follow the recommendations contained therein. If you are publishing in another venue, follow the guidelines of the publisher, if they make those available.

Otherwise, you should follow a consistent set of guidelines. Note that this is not the same as saying "always use a hyphen" or "never use a hyphen." For instance, you would write 


  "the velocity of the flow field increased"


but 


  "the flow-field variables are . . ."


because "flow field" is a noun in the first example, and "flow-field" is an adjective in the second. There the hyphen links the connected words: "flow-field" and "variable" versus "flow" and "field variable."