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Experimental study of underexpanded round jets : nozzle lip thickness effects and screech closure mechanisms investigation

Abstract : This work provides an experimental contribution to the study of the Screech phenomenon. Various experimental techniques such as microphones array, Schlieren and Particle Image Velocimetry (PIV) together with advanced post-processing techniques like azimuthal Fourier decomposition and Proper Orthogonal Decomposition (POD) are employed. These techniques enable the evaluation of the lip thickness effects on the jets generated by two different round nozzles. The differences on the flow aerodynamics and acoustics are discussed. Then, we carry out experiments to analyse the effects of the different dominant Screech modes (B and C) on the flow characteristics. No noticeable differences are found in the mean fields. However, the fluctuation fields shows the contrary: B mode has larger fluctuation. In the last part, we investigate the Screech closure mechanism. The signature of upstream jet waves is revealed in the axisymmetric (A2) and helical (C) mode. However, the mode B does not present evidence of this instability in the flow, indicating that its closure mechanism may be bonded to another kind of waves. The conclusion from the results is that the Screech phenomenon seems be driven by different closure mechanisms.
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https://tel.archives-ouvertes.fr/tel-02025250
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Submitted on : Tuesday, February 19, 2019 - 3:41:08 PM
Last modification on : Tuesday, June 4, 2019 - 6:21:21 PM
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  • HAL Id : tel-02025250, version 1

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Thiago Lima de Assunção. Experimental study of underexpanded round jets : nozzle lip thickness effects and screech closure mechanisms investigation. Acoustics [physics.class-ph]. Université de Poitiers, 2018. English. ⟨NNT : 2018POIT2327⟩. ⟨tel-02025250⟩

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