Simulation study on modeling for design parameters analysis of free-piston tunnels

A dynamic model was designed and developed using thermodynamic mass conservation equation, energy conservation equation, flow equation of nozzle and motion equation for moving piston and design parameter analysis of free-piston tunnels was proposed. The proposed model was validated by comparing the predictions made with the dynamic model established with the experimental data reported in some of the references and used to run simulation. Simulation results indicated that the target pressure and temperature could be quickly obtained by selecting and adjusting design parameters with the proposed model while the pressure and temperature output of the reservoir were kept long stable with a pneumatic hydraulic driving device. The time domain conditions of free-piston wind tunnel could be established through numerical study at different gas source pressure. The pressure and temperature of reservoir could be obtained by adjusting the valve opening of gas source. The variable specific heat ratio has a remarkable effect on the performance of free-piston wind tunnel. For the variable specific heat ratio, the temperature and pressure of reservoir was lower than the constant specific heat ratio. It was therefore concluded that the proposed model was suitable for performing the design parameter analysis of free-piston wind tunnels, and so, it could be used to facilitate the design of free-piston wind tunnels for long working at high Mach number.