• Version
• 184 Downloads
• 6.86 MB File Size
• 1 File Count
• December 14, 2016 Create Date
• December 14, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Theoretical Investigation of Submerged Inlets at Low Speeds

The general characteristics of the flow field in a submerged air
inlet are investigated by theoretical, windetunnel, 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 compressi~
bility are also discussed.

Among the various types of air inlets considered for use with air—
craft internal flow systems is the submerged or flush inlet. As a
result of extensive experimental research by the NACA at its Ames Aero~
nautical Laboratory, reported in several papers and reviewed in refer—
ence l, a particular inlet of this type was developed (fig. 1) exhibiting
pressure recovery and drag characteristics which make it suitable for
application to aircraft.

In contrast to the nosa inlet and the wing leading-edge inlet, the
submerged inlet does not operate in essentially free—stream air. The
air entrained by the submerged inlet suffers pressure losses, the
magnitude and distribution of which may be drastically affected by the
geometry of the approach ramp.1 The design of this approach ramp, in
both profile and plan form, is a problem basic to the further develop—
ment of submerged inlets in general. Although some of the basic concepts
to be presented here regarding the flow in submerged inlets are known
(see reference 1) , the purpose of the present paper is to analyze
theoretically the relative importance of the various design parameters
and to indicate, insofar as possible, methods for calculating their
effects on the over—all performance of a submerged inlet.