![]() ![]() In the case of the Lockheed SR-71 Blackbird with part of the supersonic compression taking place inside the ducting the spike and internal cowl surfaces were curved for gradual isentropic compression. In this case the rear part of the forward-facing conical surface, together with the internal surface profile of the duct, continues the supersonic diffusion with reflected oblique shocks until the final normal shock. For higher Mach numbers part of the supersonic diffusion has to take place inside the duct, known as external/internal or mixed compression. The visible cone is a supersonic diffuser with a requirement for low loss in total pressure, and the rear, streamlined part, together with the internal surface profile of the duct, forms the subsonic diffuser, also with a requirement for low loss in total pressure as the air slows to the compressor entry Mach number.įor Mach numbers below about 2.2 all the shock compression is done externally. The rear of the cone beyond its maximum diameter, rear-facing and unseen inside the duct, is shaped for a similar reason to the protruding front part. The conical body may be a complete cone centerbody in a round inlet ( MiG-21), a half cone in a side-fuselage inlet ( Lockheed F-104 Starfighter) or a quarter cone in a side-fuselage/underwing inlet ( General Dynamics F-111 Aardvark). For higher speeds a more smoothly contoured transition between cone angles may be used in what is known as an isentropic spike ( Marquardt RJ43 ramjet). In this case a biconic cone is required with two angles ( the Bristol Thor ramjet has 24 and 31 degrees for a design speed of Mach 2.5). A higher design speed may require two oblique shocks focussed on the lip to maintain an acceptable pressure recovery and pass maximum airflow. The inlet passes its maximum airflow and achieves its maximum pressure recovery. The cone angle is chosen such that, at the design condition for the inlet (Mach 1.7 for the English Electric Lightning inlet ), the shock wave that forms on its apex coincides with the cowl lip. Īn inlet with cone may be used to supply high pressure air for ramjet equipment which would normally be shaft-driven on a turbine engine, eg to drive turbopumps for the fuel pump on the Bristol Thor ramjet and hydraulic power on the Bristol Bloodhound missile. If less than that required then the pressure recovery is lower which reduces engine thrust. If the flow is more than that required by the engine then shock position instability(buzz) can occur. Also, the cone, together with the inlet cowl lip, determine the area which regulates the flow entering the inlet. ![]() Slowing the air to low supersonic speeds using a cone minimizes loss in total pressure (increases pressure recovery). An inlet cone, as part of an Oswatitsch-type inlet used on a supersonic aircraft or missile, is the surface on which supersonic ram compression for a gas turbine engine or ramjet combustor takes place through oblique shock waves. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |