there have been a bunch of these on the forum recently. take a look and see if some of the suggestions will help. here's one of them: https://forum.solidworks.com/message/348299#348299
regarding the file that you uploaded, it was just a surface model. i think you forgot to post the one that you were having trouble with.
the big thing here is that you need a solid and it needs to not have any gaps/pockets in it if you can avoid it. if you can't, make sure internal spaces are ignored in your simulation.
otherwise, setting up an external flow analysis should be simple like the ones in the tutorials/training.
i'd suggest starting with a big block to get the process down then just use a replace component or similar to remove the block and drop your model in. if you have problems, you know it isn't the setup, it is your model. at that point you need to do the standard tests like checking for interferences, making sure it survives ctrl-q with verification on rebuild, no import problems, no invalid contacts...etc.