Preprint 2002-038

Multidimensional Transonic Shocks and Free Boundary Problems for Nonlinear Equations of Mixed Type

Gui-Qiang Chen and Mikhail Feldman

Abstract: We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written into a second-order, nonlinear elliptic-hyperbolic equation of mixed type for the velocity potential. The transonic shock problem can be formulated as the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.

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Gui-Qiang Chen, <>
Mikhail Feldman, <>
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<> June 27 2002.

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