Inward-Turning Streamline-Traced Inlet Design Method for Low-Boom, Low-Drag Applications

Abstract

A new design method for inward-turning, streamline-traced inlets is presented. Resulting designs are intended for low supersonic, low-drag, low-boom applications such as that required for NASA's proposed low-boom flight demonstration aircraft. A critical feature of these designs is the internal cowl lip angle that allows for little or no flow turning on the outer nacelle. Present methods using conical-flow "Busemann" parent flowfields have simply truncated, or otherwise modified the stream-traced contours to include this internal cowl angle. Such modifications disrupt the parent flowfield, reducing inlet performance and flow uniformity. The method presented herein merges a conical flowfield that includes a leading shock with a truncated Busemann flowfield in a manner that minimizes unwanted interactions. A leading internal cowl angle is now inherent in the parent flowfield, and inlet contours traced from this flowfield retain its high performance and good flow uniformity. CFD analysis of a candidate inlet design is presented that verifies the design technique, and reveals a "starting" issue with the basic geometry. A minor modification to the cowl lip region is shown to eliminate this phenomenon, thereby allowing starting and smooth transition to sub-critical operation as back-pressure is increased. An inlet critical-point total pressure recovery of 96% is achieved based on CFD results for a Mach 1.7 freestream design. Correction for boundary-layer displacement thickness, and sizing for a given engine airflow requirement are also discussed.

Vortex Generators in a Streamline-Traced, External-Compression Supersonic Inlet

“…11 The axisymmetric parent flowfield for the STEX inlet was established using the Otto-ICFA-Busemann method. 2 The internal angle of the leading edge was -5.0 degrees. The parent flowfield contained a leading, weak oblique shock followed by an isentropic supersonic compression which ended with a strong oblique shock that decelerated the flow to Mach 0.9 and turned the flow into the axial direction.…”

“…Introduction Recent studies have examined streamline-traced, external-compression (STEX) supersonic inlets for turbinepowered aircraft flying at Mach 1.6. [1][2][3] A STEX inlet is characterized by an external supersonic diffuser obtained from tracing streamlines through an axisymmetric, inward-turning parent flowfield containing a strong, oblique terminal shock. Section III will provide further details on the STEX inlet.…”

SUPIN: A Computational Tool for Supersonic Inlet Design

“…A change in the design methodology for the STEX inlet was introduced in Ref. 18, which discussed a novel parent flowfield for the streamline tracing that contained the leading edge oblique shock and the outflow conical shock within the analytic flowfield. This methodology was summarized in the sub-section above discussing the external supersonic diffuser for the streamline-traced inlets.…”

“…This displacement or "cut-out" allows for subsonic spillage, which was shown in Ref. 18 to be important for smooth variation of the shock system over the variation of the inlet flow rate. The STEX inlet of Fig.…”

“…16 Later papers have discussed the use of SUPIN in inlet design studies and the methodology of the streamline-traced inlet design. 17,18,19 This paper describes the latest capabilities of SUPIN. Section II discusses the inlet types available within SUPIN.…”