  We investigate the chirality of phonon modes in twisted bilayer WSe2 and
demonstrate distinct chiral behavior of the $K/K^\prime$ valley phonons for
twist angles close to $0^{\circ}$ and close to $60^{\circ}$. In particular,
multiple chiral non-degenerate $K/K^\prime$ valley phonons are found for twist
angles near $60^{\circ}$ whereas no non-degenerate chiral modes are found for
twist angles close to $0^\circ$. Moreover, we discover two sets of emergent
chiral valley modes that originate from an inversion symmetry breaking at the
moir\'{e} scale and find similar modes in moir\'{e} patterns of
strain-engineered bilayers WSe2 and MoSe2/WSe2 heterostructures. At the energy
gap between acoustic and optical modes, the formation of flat phonon bands for
a broad range of twist angles is observed in the twisted bilayer WSe2. Our
findings are relevant for understanding electron-phonon and exciton-phonon
scattering in moir\'e materials and also for the design of phononic analogues
of flat band electrons.
