Pressure records analysis in an unsteady expansion wave

Some new experimental results on the rarefaction wave form deduced from pressure records obtained just upstream of the diaphragm in the driver chamber of a shock tube or in a Ludwieg tube are reported and their interpretation in terms of the diaphragm opening process and boundary layer development is discussed. A one-dimensional model is shown to be sufficient to describe the expansion wave at its beginning when gas expands into a driven tube. Records at large distances from the diaphragm experimentally confirm the laminar boundary layer growth theory developed by Hall (1972). The boundary layer displacement thickness just before transition to turbulence has been determined to be 0.4 mm and the corresponding Reynolds number is 7200.