The expansion of gas from a wedge with small angleinto a vacuum

In this paper, the problem of the expansion of a wedge of gas into vacuum isinvestigated. Let θ be the half angle of the wedge. For a givenθ̄ determined by the adiabatic exponent γ, we prove theglobal existence of the solution through the direct approach in the caseθ≤θ̄, extending the previous result obtained by Li, Yang and Zheng.Our analysis relies on the special symmetric structure of the characteristic form as wellas characteristic decompositions.