DIRECT NUMERICAL SIMULATION OF DECAYING COMPRESSIBLE ISOTROPIC TURBULENC

Statistical characteristics of turbulent flow and its compressibility effect within decaying isotropic turbulence have been studied using direct numerical simulation through fifth-order WENO scheme. The research reveals that turbulent kinetic energy mainly comes from solenoidal velocity field and small scale motions are sensitive to the compressibility. As the compressibility increases, turbulent kinetic energy transport between the large and the small turbulent motions becomes more rapid. Furthermore, the increasing initial turbulent Mach number leads to a fast rise of fraction of dissipation rate due to dilatation. Through scaling law analysis, it is shown that transverse velocity structure function (TVSF) still satisfies extended self-similarity (ESS), so does longitudinal velocity structure function (LVSF) at low order; while if the order of LVSF is high (p ≥ 5), the ESS will not hold true. For weakly compressible turbulence, the transverse turbulent velocity fluctuations are more intermittent than the longitudinal fluctuations as same as that in the incompressible turbulence. In contrast, longitudinal fluctuations are more intermittent than transverse fluctuations for strongly compressible turbulence.