Absorption of characteristics by sonic curve of the two-dimensional Euler equations

We explore the reflection off a sonic curve and the domain of determinacy,via the method of characteristics, of self-similar solutions to thetwo dimensional isentropic Euler system through severalexamples with axially symmetric initial data. We find thatcharacteristics in some cases can be completely absorbed by the sonic curveso that the characteristics vanish tangentially into the sonicboundary, exemplifying a classical scenario of the Keldysh type;however, the characteristics can wraparound the closed sonic curve unboundedly many times, so thatthe domain of determinacy of the hyperbolic characteristic boundaryvalue problem or the Goursat problem exhibit layered annulus structures.As the number of layers increases, the layers become thinner, and thesolution at an interior point of the domain depends eventually on theentire boundary data.