I'd like to know whether it's possible to clear the NTFS dirty bit in bash script.
Doing so is inherently unsafe. ntfsprogs has plans for a ntfsck, which would allow you to safely fix up and mark as clean a filesystem. However, the tool has not been implemented yet.
That said, simply clearing the dirty bit is a recipe for trouble. If a filesystem crashed you must run recovery before using it, which for now requires Windows as far as I know.
Why do you want to do that? Maybe there's a better way to do whatever you're trying to accomplish?