Streamwise vorticity in viscous, compressible, steady flow about aircraft

Streamwise vorticity in viscous, compressible, steady flow about aircraft is analysed on the basis of the steady Reynolds-averaged Navier–Stokes equations. It is shown, that streamwise vorticity can develop in the presence of stream-normal vorticity and can be non-negligible only inside e.g. boundary layers, shock layers, viscous (turbulent) wakes, jet exhausts and propeller slipstreams, but also along streamlines leaving such viscous and heat conduction dominated flow regions on their downstream side (e.g. downstream of shock layers). However, the actual development of streamwise vorticity then still depends on such local flow characteristics as e.g. streamline curvature and streamline convergence or divergence. Two illustrative examples are discussed.