A New-Conception, Electromagnetically Controlled, Diaphragmless Shock Tube

A new conception, electro-magnetically controlled, diaphragmless shock tube was realized and tested in the laboratories of University of Florence. A piston separates the co-axial driver and driven sections. The piston is kept in position by a force of an electromagnet acting on an iron disc linked to its rod. In order to obtain very short opening time, light materials were tested for moving devices: aluminum, ergal, titanium and iron. Opening time was measured using contact sensors. Several different dimensionless driven section lengths were tested by changing the driven section length and by reducing the driven section diameter. The influence of the two factors on shock presence and shock formation was analyzed separately. Tests were carried out for driver-to-driven pressure ratios of up to 22, obtaining shock waves at Mach number of up to 1.70 with a difference from the theoretical value for a straight shock tube of 9%. A configuration for increasing the useful test time after the shock passage is also proposed and tested. The system realized is simple, easy-to-use, quite cheap and can be a very useful way of obtaining a reproducible shock wave. The shock tube details and the test results are reported below.