Abstract
An experimental study was conducted to determine the effect of choking on the aerodynamic and acoustic performance of a supersonic inlet. The investigated inlet was a prototype model of a mixed compression, axisymmetric supersonic inlet designed for the high speed civil transport aircraft. A 10·4 cm (4·1 in) turbofan engine simulator was used in conjunction with the inlet. The inlet was tested with the centerbody in the fully extended position at different fan speeds. Results show that “soft choking”, as characterized by a reduction in forward propagating fan noise, can occur when the Mach number at the inlet throat exceeds 0·5. In the forward sector (0°–60° from the inlet axis), the overall sound pressure level was reduced by about 7 dB as the fan speed increased from 50,000 to 70,000 rpm, due to the increase in the Mach number at the inlet throat. Additional comparison was made between the inlet configurations with the centerbody fully extended and fully retracted at a fan speed of 50,000 rpm. The results show that the higher Mach number at the inlet throat for the full retracted centerbody configuration was successful in reducing the overall sound pressure level by about 4 dB between 0° and 30° angular sector. While there is no measurable difference in the total pressure recovery for the two inlet configurations, there is, however, a significant increase in the circumferential flow distortion at the fan face for the higher throat Mach number test case.
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