NACA Duct Tech Note 2323

Written by NACA, Alvin H Sacks and John R Spreiter.

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National Advisory Committee for Aerodynamics (NACA)
Technical Note 2323
"Theoretical Investigations of Submerged Inlets at Low Speeds"
By Alvin H Sacks and John R Spreiter


The general characteristics of the flow field in a submerged air inlet are investigated by theoretical, wind-tunnel, and visual-flow studies.

Equations are developed for calculating the laminar and turbulent boundary-layer growth along the ramp floor for parallel, divergent, and convergent ramp walls, and a general equation is derived relating the boundary-layer pressure losses to the boundary-layer thickness.  It is demonstrated that the growth of the boundary layer on the floor of the divergent-ramp inlet is retarded and that a vortex pair is generated in such an inlet.  Functional relationships are established between the pressure losses in the vortices and the geometry of the inlet. 

A general discussion of the boundary layer and vortex formations is included, in which variations of the various losses and of the incremental external  drag with mass-flow ratio are considered.  Effects of compressibility are also discussed.

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