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To ease numerical computation problems, the exit Mach number of the flow is assumed to have been 1.02 instead of the sonic Mach number, 1.00. All length dimensions, x and y, are normalized to vent diameter. The model is symmetric about axis of vent, so it is split into two halves here for conciseness. On left, the characteristics are shown as thin lines radiating from corner of vent. Boundary of flow is assumed to have been at constant pressure, 8.7 x 10^4 Pa (0.87 bar). The peripheral intercepting shock formed by reflection of the expansion waves from this boundary is shown as dashed line.