Jet engine performance: Difference between revisions

Revision as of 05:15, 4 March 2025

Revision as of 08:11, 4 March 2025

Line 232:

File:B-58 Hustler (6693464445) (2).jpg|[[Convair B-58 Hustler]] early Mach 2 supersonic inlet with a centre (translating) cone which has different axial positions (5 inch travel) to reduce total pressure loss over the range of flight Mn. An oblique shock from the cone tip and a normal shock form at supersonic speeds.

File:Presadinamicass.png|Increasing loss with Mn is lessened with more shocks (urti).

File:VastersLockheed 1602SR-71A Blackbird at Evergreen Aviation & Space Museum (6586637283).jpg|A view of the entry to an SR71 Mach 3.2 mixed external-internal inlet looking in direction of airflow to the engine. The centre translating cone has 26 inches of travel between extended, up to M1.6 (shown), and fully retracted at M3.2. An oblique shock from the cone tip, an internal oblique shock from the cowl lip and a normal shock<ref>https://patents.google.com/patent/US3477455A/en,"Supersonic inlet for jet engines"</ref> give the required pressure recovery at M3.2. The boundary layers on the cone and cowl inner surface have to be removed before the final shock-wave where the flow becomes subsonic. Otherwise shock-induced separation occurs. The two removal features are just visible. The cone boundary layer is removed through the band of holes (porous bleed). The boundary layer on the cowl inner surface is removed through a shock-trap<ref>https://ntrs.nasa.gov/citations/19930090035,"Use of Shock-trap Bleed to Improve Pressure Recovery...",</ref> bleed. This ram bleed is just visible on the lower surface in front of a row of streamlined lumps called "mice" which reduce the rate of diffusion.<ref>https://www.semanticscholar.org/paper/Ramjet-Intakes-Cain/96dc23a101c094f19d185f7497755c0cb0d19ec8, "Ramjet Intakes", Cain, Figure 19</ref>

File:Inlet shock waves at Mach 2.jpg|Shock waves on a mixed external/internal inlet, as used on the [[Lockheed SR-71 Blackbird]]. The image on the right shows the inlet operating correctly with minimum pressure loss. It has 2 shockwaves, the first is visible originating at the tip of the cone and the second which results from the flow slowing from supersonic to subsonic speed is not visible as it is positioned inside the inlet. The inlet is called an external/internal or mixed compression inlet as some supersonic diffusion takes place inside the duct. The left image shows the inlet operating with excessive loss in total pressure as the internal terminal shock has been pushed forward out of the inlet.

</gallery>