Simulating Compressible Turbulence in Near-Sun Solar Wind*

In the solar wind near the Sun, enhanced density fluctuations are reported by both in-situ and remote sensing observations, indicating the importance of compressible turbulence. But the generation mechanism for the density fluctuations in the solar wind is still under debate. In this study, we use a 3D compressible MHD model based on Athena++, which includes wind expansion, a heating function, thermal conduction and radiative cooling, to simulate wind acceleration and generation of density fluctuations within 40 solar radii. Various types of energy injection are applied at the coronal base, including incompressible and compressible, coherent and random, magnetic and velocity forces. We compare resulting magnetic, velocity, and density fluctuations, as well as background wind profiles with PSP observations near the Sun. Preliminary results show that a combination of turbulence injection and a heating function is needed to match simulation results with the observations. Possible contribution from the parametric decay instability to the density fluctuations is also evaluated.