Underexpanded Supersonic Jets from Elliptical Nozzle with Aft Deck

摘要

An experimental investigation of an underexpanded supersonic jet issuing from a circular nozzle, an ellipticalnozzle, and an elliptical nozzle with an aft deck at different nozzle pressure ratios (NPRs) is reported in this paper.Static-pressure measurements over the nozzle walls were analyzed to understand the internal flow structure.Schlieren visualization and conical probe measurements were conducted to elucidate the development of the jetsissuing from the nozzles. The sound-pressure level in the near field was measured, and it was found that the screechamplitudes were 26 dB lower in the elliptical nozzle with an aft deck. The screech-tone frequencies were observed tobe above and near audible region (16 kHz) in the presence of the aft deck at NPRs 3 and 4. The jets emanating fromthe circular and truncated elliptical nozzles were observed to be flapping about the jet axis at NPRs 3 and 4. Theunsteadiness of the jet was reduced by locking the jet onto the aft deck. The centerline Mach-number decay revealedthat, due to the screeching effect, the truncated elliptical nozzle has a shorter potential core length and larger jetspreading. The flow separation and reattachment were observed over the aft-deck surface for higherNPRconditions.