Shock Front Curvature at Initial Pressures up to 700 mm Hg

Axial extents of curved shock fronts in argon were measured using thin film heat transfer gauges mounted on a plate perpendicular to the axis of a 1½-in.-diam shock tube. In interpreting the data, use was made of the theoretical shock shape. This shape was determined from previously derived formulas which apply when the boundary layer behind the shock is either laminar or turbulent, and which account in an approximate way for the influence of the flow at the foot of the shock. At low initial pressures the experimental data obtained agree well with theory and with results of other investigators. For initial pressures above 100 mm Hg, the data showed appreciable scatter, which is taken to indicate that the shock is oscillating in curvature. The scatter has the order of magnitude which follows from Freeman's theory for the damping of perturbations in shock shape, with the assumption that somewhere near the diaphragm the shock is strongly curved.