Structural stability of subsonic irrotational flows in two-dimensional infinitely long nozzles

This paper investigates the structural stability of two-dimensional subsonic irrotational inviscid flows throughout infinitely long nozzles. More precisely, we show that the smooth subsonic potential flows are structural stable under the small perturbations for the nozzle walls. The analysis of this paper is based on the standard estimates for second order quasilinear elliptic equations for the stream function.