I got slapped hard on my ear yesterday and since then there is buzzing sound and I don't have any pain just feel like air passing through my ear?

You may need to get. examined by a healthcare provider for a punctured eardrum, e.g. perforated tympanic membrane. Usual symptoms of these perforations are hearing loss, pain, bleeding, and tinnitus (or ringing in the ear). Your symptoms do not sound that serious, though a contusion to the bony structures inside the eardum may affect your hearing for a while but should heal spontaneously.
Post traumatic. tinnitus (noise in ear) is quite COMMON and generally resolves itself within a week. If it persists you should have an ear exam ( r/o perforated drum etc) Hope this helps! Dr Z.