Numerical simulation of forced acoustic gas oscillations with large amplitude in closed tube

Abstract

Nonlinear acoustic oscillations with large amplitude created in gas-filled closed tube by piston oscillating according to the harmonic law near three natural resonant frequencies are numerically studied. The movement of the medium is described by the Navier–Stokes equations for viscous compressible fluid, which are approximated through the control volume method using the OpenFoam library. The influence on the maximum pressure drop of the excited piston oscillation frequency at large amplitudes near the first resonant frequency is studied. The used numerical model allows to achieve good agreement with the experimental data for intensive gas oscillations with breaking waves. The dynamics of changes in pressure and velocity during a single period of oscillations at different natural frequencies are studied in detail. Nonlinear features for intensive shock oscillations of viscous gas in a closed tube at higher harmonics have been detected. In particular, oscillations in the pressure nodes with a frequency equal to the doubled frequency of forced oscillations of the piston at the first and higher modes resonance frequencies were found. For non-linear gas oscillations with a shock front of pressure changes in the nodes for the velocities of gas particles inside the tube, the large amplitudes of the change in particle velocities over a very short period of time are observed. The received results show that the used numerical approach is a suitable method for modeling highly nonlinear acoustic oscillations and related problems.