The Hydrodynamics of Astrophysical jets: Scaled Experiments and Numerical Simulations

Context. In the present paper we study the propagation of hypersonic hydrodynamic jets (Mach number greater then 5) in a laboratory vessel and make comparisons with numerical simulations of axially symmetric flows in the same initial and boundary conditions. The astrophysical context is that of the jets issuing from Young Stellar Objects (YSOs). Aims. In order to have a further insight into the jets from YSOs, a set of experiments and numerical simulations of hypersonic jets is performed in the range of Mach numbers from 10 to 20 and for jet-to-ambient density ratios from 0.85 to 5.4, using different gas species and observing jet lengths of the order of 150 initial radii or more. Exploiting the scalability of the hydrodynamic equations, we intend to reproduce the YSO jet behaviors as far as the jet and head velocities and elapsed times are concerned. In addition, we can make comparisons between the simulated, the experimental and the observed morphologies. Methods. In the experiments the gas pressure and temperature are increased by a fast, quasi isentropic compression by means of a piston system operating on a time scale of tens of millisecond, while the gas density is visualized and measured by means of an electron beam system. The PLUTO software for the numerical solution of mixed hyperbolic/parabolic conservation laws targeting high Mach number flows in astrophysical fluid dynamics is used. We consider axisymmetric initial conditions and carry out numerical simulations in cylindrical geometry. The code has a modular flexible structure whereby different numerical algorithms can be separately combined to solve systems of conservation laws using th