  Simulating hypersonic flow around a space vehicle is challenging because of
the multiscale and nonequilibrium nature inherent in these flows. To
effectively deal with such flows, a novel particle particle hybrid scheme
combining the stochastic particle Bhatnagar-Gross-Krook (BGK) method with
Direct Simulation Monte Carlo (DSMC) was developed recently, but only for
monatomic gases [Fei et. al., J. Comput. Phys. 2021]. Here this work is
extended to the particle-particle hybrid method for polyatomic gases. In the
near continuum regime, employing the Ellipsoidal Statistical BGK model proposed
by Y. Dauvois, et. al. [Eur. J. Mech. B Fluids, 2021] with discrete levels of
vibrational energy, the stochastic particle BGK method is first established
following the idea of the unified stochastic particle BGK (USPBGK) scheme. In
the fluid limit, it has been proven to be of second order temporal and spatial
accuracy. Then, the USPBGK scheme with rotational and vibrational energies is
combined with DSMC to construct a hybrid method for polyatomic gases. The
present hybrid scheme is validated with numerical tests of homogenous
relaxation, 1D shock structure and 2D hypersonic flows past a wedge and a
cylinder. Compared to traditional stochastic particle methods, the proposed
hybrid method can achieve higher accuracy at a much lower computational cost.
Therefore, it is a more efficient tool to study multiscale hypersonic flows.
