K of the subsonic flowfield in the vicinity of air inlets or wedges is a necessity for engineering design and analysis. This Note presents the results of numerical solutions for two-dimensional subsonic compressible flows. In order to obtain a solution it is necessary to introduce several severe restraints such as field representation, field boundaries, and body surface configuration changes. The effects of these restraints have been investigated and the optimum methods are presented. Emmons, Amick, and other investigators' have treated the various methods of solution of the simultaneous difference equations that represent the continuous flowfield in terms of a discretized flowfield. Fox has presented some methods for representing the discontinuous finite slope changes of bound-

Numerical solution of subsonic compressible flow at two-dimensional inlets.

Two schemes were studied in an attempt to reduce the drag of a supersonic inlet at subsonic speeds. One of the methods is to use a retractable airfoil in front of the cowl to generate thrust. The second method involves hinging the cowl lip inward so that the captured airflow is choked, thus lowering the pressures on the external surfaces. Both schemes were successful in reducing the drag at captured airflow rates less than the choking point of the plain inlet. Although the drag was not reduced below the critical drag of the plain inlet, the tests indicate that this may be possible.

Studies of drag-reduction methods for subsonic operation of supersonic inlets.

Multidisciplinary Design Optimization of an Aircraft Considering Path-Dependent Performance

Pressure distribution data are provided for a supersonic rectangular inlet at subsonic speeds. Variations in cowl and ramp geometry as well as sideplate sweep were investigated. Tests were made in the Langley 16-foot transonic tunnel and the Langley high speed 7- by 10-foot tunnel for Mach numbers of 0.6, 0.7, and 0.8. Angles of attack investigated were 0 deg, 4 deg, and 8 deg for a range of mass flow ratios.

Pressure distributions for a rectangular supersonic inlet at subsonic speeds

Axisymmetric inlet design for turboramjet powered hypersonic cruise vehicle, examining effects of spillage and cowl drags on air flow characteristics

A comparative study of three axisymmetric inlets for a hypersonic cruise mission

The subsonic-transonic drag of supersonic inlets appears to be a subject that has been largely neglected in the transition from subsonic to supersonic design-point flight. Now that more emphasis is placed on off-design performance of supersonic aircraft, more information is required on this subject. Accordingly, experimental data were obtained on subsonictransonic drag of two types of supersonic inlets. The types investigated were two-dimensional and axisymmetric plug inlets. The two-dimensional inlets were of the single-ramp mixed compression variety. The axisymmetric inlets had a conical plug and were also of the mixed-compression type. The range of variables studied was as follows: two-dimensional inlet ramp angle, 6°-12°; axisymmetric inlet conical plug half-angle, 10°-18°; two-dimensional inlet throat-capture area ratio, 0.32-0.80; and axisymmetric inlet throat-capture area ratio, 0.13-0.80. It was found that two-dimensional inlets have higher additive drags than axisymmetric inlets of the same area ratio and initial angle. This conclusion is the same as in supersonic flight.

George L. Muller

Papers

Subsonic-transonic-drag of supersonic inlets.