Intake ramp

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An intake ramp is flat rectangular plate-like device, within a 2-Dimensional air intake, designed to generate a, rearward leaning, oblique shock wave, to aid the inlet compression process. The ramp sits at an acute angle to deflect the intake airstream from the longitudinal direction. At supersonic flight speeds, the deflection of the airstream creates an oblique shock wave at the forward end of the ramp. Air crossing the shock wave suddenly slows to a lower Mach number, thus increasing static pressure. However, shock waves are non-isentropic, so there is a reduction in total pressure relative to that of the freestream. Although there are reflected oblique shock waves and a weak normal shock wave generated downstream, this form of intake is more efficient (i.e. higher total pressure recovery) than the equivalent pitot intake, particularly at high supersonic flight speeds.

Ideally, the oblique shockwave should intercept the air intake lip, thus avoiding air spillage and pre-entry drag on the outer boundary of the deflected streamtube. For a fixed geometry intake at zero incidence, the Shock-on-Lip condition can only be achieved at one particular flight Mach number, because the angle of the shock wave (to the longitudinal direction) becomes more acute with increasing flight Mach number.

Some supersonic intakes feature two or more ramps, operating in series, to generate multiple oblique shock waves. Each downstream ramp is steeper in inclination than the previous ramp. These intakes are usually more efficient than single (oblique) shock wave inlets.

Variable geometry intakes, such as those on Concorde aircraft , vary the ramp angle to focus the oblique shock wave/s onto the intake lip. On at least one occasion, a Concorde ejected a complete intake ramp forwards, out of the intake system, owing to the back-pressure created by a violent compressor surge of one of the Rolls-Royce Olympus 593 engines.