Experimental study for multi-lobed mixer high bypass exhaust systems for subsonic jet noise reduction. II - Acoustic results

Salikuddin, M.; Martens, Steven; Janardan, B. A.; Shin, Hyun Wook; Majjigi, R. K.

doi:10.2514/6.1999-1988

Cited by 6 publications

(3 citation statements)

References 3 publications

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“…As with tabbed nozzles, this vorticity leads to increased mixing and reduced jet plume length [1][2][3][4][5]. As opposed to other noise reduction technologies, such as forced mixers, chevron nozzles are capable of reducing engine exhaust noise while imposing minimal engine performance penalty and a nearly insignificant weight impact [6][7][8]. An extensive effort conducted by researchers at NASA Glenn Research Center identified a set of chevron nozzle configurations providing reductions in the jet component of effective perceived noise level (EPNL) of 2-3 EPNdB with minimal loss of nozzle thrust [6].…”

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confidence: 98%

Near-Field Investigation of Chevron Nozzle Mechanisms

2008

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A detailed investigation into the effect of chevron nozzles on the near-field acoustics of a separate flow exhaust system was conducted at the University of Cincinnati Anechoic Test Facility. Chevrons with varying numbers of lobes and levels of penetration were selected to provide insight into the effects of these geometric parameters on the acoustic near field. Tests were conducted at two different nozzle operating conditions and the chevrons were shown to produce substantial modifications to the near field over a wide range of frequencies. The chevrons were most effective at lower frequencies where the peak noise region was reduced by 5-7 dB and dramatically reduced in size. At higher frequencies, the chevrons provided strong noise suppression downstream of approximately seven equivalent nozzle diameters with increases closer to the nozzle lip. The nozzle penetration was shown to have the most significant impact on the acoustic near field with more subtle differences being seen with respect to the number of chevron lobes. Nomenclature f = frequency M = jet exhaust Mach number St = Strouhal number T = temperature V = jet exhaust velocity V mix = mixed velocity, mass averaged velocity V shear = nozzle shear velocity (V p V s ) Subscripts o = total or stagnation property p = primary or core flow s = secondary or fan flow

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confidence: 98%

Near-Field Investigation of Chevron Nozzle Mechanisms

2008

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“…The excess high frequency noise is clearly visible at other operating conditions as well. Figures 7,8,9 show that the excess noise is broadband in nature. The mixed jet mean flow external to the nozzle is mostly subsonic for the mid and low power conditions, except for a small supersonic region near the maximum curvature of the external plug near the nozzle exit where the flow accelerates in a convergent-divergent nozzle and a weak shock (expansion followed by compression) is formed, as illustrated in Figure 10.…”

Section: Farfield Noise Spectramentioning

confidence: 97%

“…Many past investigations studied internal mixing and the noise effects of various lobe mixers for the nozzles with internal plugs, Refs. [5][6][7][8] While it is expected that future commercial supersonic engines will likely have some form of internal lobe mixer for the thermodynamic reasons, the engine will also most likely have an external plug for optimal jet expansion, and performance to minimize the boattail drag and sonic boom at cruise. 2 Recently Bridges and Wernet 9 were the first authors to perform a systematic study of the noise from internally mixed jets with an external plug, with the focus on the farfield noise effects of having both internal mixing and an external plug.…”

Section: Introductionmentioning

confidence: 99%

Jet noise of a low bypass turbofan with internal mixing and external plug

Pastouchenko,

Ramakrishnan,

Morris

et al. 2024

International Journal of Aeroacoustics

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Jet noise generated by turbofan engines which are designed for supersonic aircraft operation is expected to remain a challenge for the aerospace industry. For civil supersonic transport, low bypass ratio engines with internal mixing and external plugs are currently seen as promising exhaust architecture to meet aircraft mission and certification requirements. Measurements of the noise from a representative low-bypass ratio long duct mixed flow with external plug exhaust configuration were made, along with corresponding steady-RANS and LES analyses. The measured data showed excess high frequency noise across a wide range of operating conditions as compared to an equivalent single stream jet, or an equivalent uniform jet with internal plug. The absolute levels of the excess noise were relatively insensitive to forward flight, and the excess noise was most dominant when the primary and secondary streams had large velocity and temperature mismatch just upstream of the internal mixer. Preliminary indications from the LES analysis also indicated that significant pressure fluctuations, at the same frequencies which are insensitive to forward flight, develop inside the nozzle as the internal shear layer from the mixer grows and gets accelerated by the external plug. Parametric study test measurements on the fan and core operating conditions were performed, providing support for the hypothesis that the excess noise is generated as the internal shear layer, starting inside the nozzle, gets accelerated by the plug and passes through the weak shock at the nozzle exit where the flow accelerates more and turns over the external plug.

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