On the existence of weak solutions to the three-dimensional steady compressible Navier-Stokes equations in bounded domains

We prove the existence of a weak solution to the three-dimensional steady compressible isentropic Navier-Stokes equations in bounded domains for any specific heat ratio γ> 1. Generally speaking, the proof is based on the new weighted estimates of both pressure and kinetic energy for the approximate system which result in some higher integrability of the density, and the method of weak convergence. Comparing with [12] where the spatially periodic case was studied, here we have to control the additional integral terms of both pressure and kinetic energy involving with the points near the boundary which become degenerate when the points approach the boundary. Such integral terms are estimated using some new techniques, i.e., we use the techniques of the mirror image and boundary straightening to prove that the weighted estimates of both pressure and kinetic energy for the points near the boundary can be controlled by the weighted estimates for the points on the boundary. Moreover, we prove that once the weighted estimates of the kinetic energy in the direction of the unit normal to the boundary are bounded, we can control the weighted estimates of the total energy on the boundary.

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