Flow Oscillation in Dual-Bell Nozzle at Low-Altitude Operation

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  • デュアルベルノズルの低高度運転時における流体振動
  • デュアルベルノズル ノ テイコウド ウンテンジ ニ オケル リュウタイ シンドウ

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Abstract

Unsteady flow characteristics in a dual-bell altitude compensation nozzle at low altitude operation modes are examined. At the low altitude operation mode, a jet separation point is fixed at the nozzle wall inflection. However, experimental and numerical results show that three modes of periodic jet fluctuations take place at certain range of nozzle pressure ratios. The lowest frequency mode is a symmetric modes and is considered to be caused by the acoustic resonance in longitudinal direction in the extension part of the nozzle. Two kinds of asymmetric modes have higher frequency than the symmetric mode. According to the numerical results, one of them is a jet screech tone caused by the convection of large scale vortices beside the separated jet. The other mode has the same frequency with a resonance mode in the diametrical direction of the cross section of the extension part.

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