The influence of the equation of state on the cellular structure of gaseous detonations

The propagation of multidimensional gaseous detonations at elevated pressures was investigated numerically. Initial conditions at which deviations from ideal gas are expected (i.e., p0 > 2 MPa) were used to assess whether real gas effects influence their multi-cellular structure. The simplest equation of state that accounts for real gas effects was selected, Noble–Abel, and compared with the results obtained using perfect gas. Approximate and exact relationships are provided for the von-Neumann and Chapman–Jouguet states, as well as sound speeds, for both equations of state. Results show that real gas effects alter the multi-cellular structure of gaseous detonations at elevated pressures. Moreover, neglecting these effects renders a more irregular structure than that obtained when real gas effects are reinstated. The source of the perceived instabilities was identified as a Mach bifurcation due to jetting and their growth was related to a shear layer triple point interaction, giving birth to new triple points. The more unstable structure seems to arise from an effective change in the isentropic coefficient that is not included in the perfect gas formulation.