Methods to Improve the Accuracy of Acoustic Measurements in Small Scale High Speed Jets

Modern military aircraft jet engines are designed with variable geometry nozzles to provide optimum thrust in different operating conditions, depending on the flight envelope. However, the acoustic measurements for such nozzles are scarce, due to the cost involved in making full scale measurements and the lack of details about the exact geometry of these nozzles. Thus the present effort at The Pennsylvania State University and the NASA Glenn Research Center-in partnership with GE Aviation is aiming to study and characterize the acoustic field produced by supersonic jets issuing from converging-diverging military style nozzles. An equally important objective is to validate methodology for using data obtained from small and moderate scale experiments to reliably predict the most important components of full scale engine noise. The experimental results presented show reasonable agreement between small scale and moderate scale jet acoustic data, as well as between heated jets and heat-simulated ones. Unresolved issues however are identified that are currently receiving our attention, in particular the effect of the small bypass ratio airflow. Future activities will identify and test promising noise reduction techniques in an effort to predict how well such concepts will work with full scale engines in flight conditions.

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“…Eq. (1) summarizes the different steps that lead to the PSD per unit Strouhal number as explained in Kuo, Veltin and McLaughlin [6].…”

Section: Data Processing and Comparison Proceduresmentioning

confidence: 99%

On the Scaling of Small, Heat Simulated Jet Noise Measurements to Moderate Size Exhaust Jets

McLaughlin

Bridges

Kuo

2010

16th AIAA/CEAS Aeroacoustics Conference

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“…The fully expanded diameter is the diameter of the jet flow near the nozzle exit after the jet has either expanded or contracted due to pressure differences from the atmosphere. Equation (1) summarizes the different steps that lead to the PSD per unit Strouhal number as explained in Kuo et al [25].…”

Section: B Acoustic Measurements and Data Processingmentioning

confidence: 99%

“…Three corrections are then applied to the raw sound pressure level (SPL) to compute the lossless SPL as explained in Kuo, Veltin, and McLaughlin [25]. Data are corrected for microphone spectral response characteristics based on the manufacturers descriptions of each individual microphone obtained during the factory actuator calibration (∆C act ( f )) including the appropriate free field response (∆C f f ( f )).…”

Section: B Acoustic Measurements and Data Processingmentioning

confidence: 99%

Supersonic Jet Noise Reduction by Nozzle Fluidic Inserts with Simulated Forward Flight

Powers

Kuo

McLaughlin

et al. 2014

20th AIAA/CEAS Aeroacoustics Conference

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The noise produced by supersonic, high temperature jets that exhaust from military aircraft is becoming more of a disturbance. Methods to reduce the noise produced from these jets in a realistic full-scale environment is difficult. This study describes the development and analysis of fluidic inserts for supersonic jet noise suppression. Distributed blowing within the divergent section of the military-style convergent divergent nozzle alters the shock structure of the jet in addition to creating streamwise vorticity for the reduction of mixing noise. Enhancements to the fluidic insert design have been performed along with experiments for a large number of injection parameters and core jet conditions. It has been shown that the noise reduction of the fluidic inserts is most heavily dependent on the momentum flux ratio between the injector and core jet. Maximum reductions of approximately 5.5 dB OASPL have been observed with practical mass flow rates and injection pressures. The first measurements with fluidic inserts in the presence of a forward flight stream have been performed. Optimal noise reduction occurs at similar injector parameters in the presence of forward flight. Fluidic inserts in the presence of a forward flight stream were observed to reduce the peak mixing noise by nearly 4 dB OASPL and the broadband shock-associated noise by nearly 3 dB OASPL.

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“…The processing yields the power spectral density (PSD) with a frequency resolution of ∆f = 74 Hz or ∆f = 296 Hz, which is then converted to a decibel (dB) scale using a reference pressure of 20µP a. Three corrections are then applied to the raw sound pressure level (SPL) to compute the lossless SPL as explained in Kuo et al 16 The frequency range of the PSU-measured spectra shown in this paper is between 500 Hz to 100 kHz. Finally, the spectra are non-dimensionalized to SPL per unit Strouhal number, where the Strouhal number is defined as S t = f /f c , with f c the characteristic frequency of the jet defined by f c = U j /D j , U j is the fully expanded jet velocity, and D j is the fully expanded diameter of the jet plume.…”

Section: Iva Jet Noise Facility and Instrumentationmentioning

confidence: 99%

Design and Analysis of a Supersonic Jet Noise Reduction Concept

Pilony

Powers

McLaughlin

et al. 2014

52nd Aerospace Sciences Meeting

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The design and analysis of a simple jet noise reduction concept is discussed. The concept is intended for use on the type of supersonic exhaust nozzles typically employed on tactical aircraft. The concept addresses both broadband shock associated noise (BBSAN), and turbulent mixing noise. BBSAN is addressed through a reduction in the effective exhaust area, which reduces the strength of the shock cell structure in the jet. Turbulent mixing noise is reduced by enhancement of mixing in the jet shear layer, which creates a shorter region of strongly turbulent flow, and breaks up the large scale turbulent structures. This paper describes an active control device that deflects a fraction of the adjustable seals in the divergent section of the engine exhaust nozzle. After takeoff, the deflected seals would be returned to their undeflected position. Very favorable jet noise reductions are demonstrated at multiple observer angles for nominal takeoff conditions.

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Methods to Improve the Accuracy of Acoustic Measurements in Small Scale High Speed Jets

Cited by 29 publications

References 6 publications

On the Scaling of Small, Heat Simulated Jet Noise Measurements to Moderate Size Exhaust Jets

On the Scaling of Small, Heat Simulated Jet Noise Measurements to Moderate Size Exhaust Jets

Supersonic Jet Noise Reduction by Nozzle Fluidic Inserts with Simulated Forward Flight

Design and Analysis of a Supersonic Jet Noise Reduction Concept

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