Simplified Navier-Stokes equations have found application as an alternative to the complete Navier-Stokes equations for the simulation of viscous gas flows in regions of large dimensions, when there is a predominant direction of the flow [1–4]. In the present paper, flows in wind tunnel nozzles are investigated on the basis of this model. Flows in conical and profiled axisymmetric hypersonic nozzles are calculated in a wide range of Mach and Reynolds numbers. Good agreement with the experiment is obtained. The important role of viscous-inviscid interaction in nozzles for large hypersonic Mach numbers is shown.