Your B. nodosa might just need more light (that is, if it's large/mature enough to flower... Could be too young?), they like Cattleya-type lighting.... *but, they have to be acclimated to the bright light, don't just stick it in the sun
I've also heard that B. nodosa is one of those that needs a "Bloom Booster" type fertilizer (higher phosphate, which is the "P" in the NPK), in the fall...
Read thru this culture sheet, they are very informative, and w/ most of the culture sheets, you pay like $1 per sheet, but this one is a freebie (an example sheet, to show what u get when u order the Baker's Culture Sheets)
Brassavola nodosa Culture