The effect of diaphragm opening time on the feasibility of tuned operation in free piston shock tunnels

The effect of diaphragm opening time on the feasibility of tuned operation is analyzed by parametric calculations. The effect on the duration of pressure holding is also investigated. Characteristic parameters are defined to show the effects of dimensions, operation conditions and diaphragm opening time. It is shown that diaphragm opening time needs to be less than a certain limit to achieve tuned operation. The limit depends on pressure at diaphragm rupture and the ratio of diameters between a downstream shock tube and a compression tube. The permissible diaphragm opening time is also proportional to the length of the compression tube. The existence of the limit required for tuned operation is shown to be caused by the increase of pressure in the driver gas during the diaphragm opening. Moreover, the effect of diaphragm opening time on the duration of the pressure holding is shown to be weak once tuned operation becomes feasible.