  We analyze spin and orbital angular momenta in monochromatic acoustic wave
fields in a homogeneous medium. Despite being purely longitudinal (curl-free),
inhomogeneous acoustic waves generically possess nonzero spin angular momentum
density caused by the local rotation of the vector velocity field. We show that
the integral spin of a localized acoustic wave vanishes in agreement with the
spin-0 nature of longitudinal phonons. We also show that the helicity or
chirality density vanishes identically in acoustic fields. As an example, we
consider nonparaxial acoustic Bessel beams carrying well-defined integer
orbital angular momentum, as well as nonzero local spin density, with both
transverse and longitudinal components. We describe the nontrivial polarization
structure in acoustic Bessel beams and indicate a number of observable
phenomena, such as nonzero energy density and purely-circular transverse
polarization in the center of the first-order vortex beams.
