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

Abstract

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.

Effects of Jet Temperature on Broadband Shock-Associated Noise

“…Second, the small-scale jet measurements at Pennsylvania State University (with a nozzle exit diameter of 1.3 cm) replicate, with reasonable accuracy, the acoustic field of the moderate scale jet facility at The Boeing Company (with a nozzle exit diameter of 6.2 cm). This result has provided similar evidence to that obtained from comparisons of the Pennsylvania State University supersonic jet acoustic data with NASA data for noise from military-style nozzles [27]. From these figures, it is evident that the jet heating introduces modest changes in the magnitude and peak frequency of BBSAN for low-to midrange values of jet total temperature.…”

“…Miller and Veltin [26] showed a good agreement of the mean flow properties between experimental data from helium-air mixture jets and a numerical calculation of heated air jets. Recent careful comparisons [27] between the measurements conducted at Pennsylvania State University with the measurements performed in other facilities have shown very good agreement when matching the acoustic velocity of the helium-air mixture jet to that of a heated jet following a procedure developed by Doty and McLaughlin [24] over 10 years ago.…”

“…The microphones used are 3.2 mm (1∕8 in:) pressure-field microphones: type 4138 from Brüel and Kjaer, and type 40DP from G.R.A.S. Details of the data acquisition methodology, analysis, and presentation are described by McLaughlin et al [27].…”

Flow structure and acoustics of supersonic jets from conical convergent-divergent nozzles

“…23 Narrow-band spectra measured for the same nozzle revealed details of the spectral features of screech and broadband shock-associated noise. 24,25 The present paper expands upon the initial evidence presented by Munday et al 22 and Liu et al 23 in improving the quality of the flow measurements with improved shadowgraph images and by adding Particle Image Velocimetry (PIV) data. The present paper also nearly doubles the domain over which near-field pressure fluctuations are measured and expands the number of operating conditions (M j or NPR) over which far-field acoustic data is presented.…”

Toward Active Control of Noise from Hot Supersonic Jets

“…Approved for Public Release -Distribution is Unlimited propagation effects through the standard atmosphere are not scalable (these discrepancies have also been observed by Gallagher (1982), Petitjean et al (2006), McLaughlin et al (2010) and Saxena et al (2009)). As an example, a successful capture of cumulative non-linear waveforms produced by a full-scale engine by Gee et al (2008) comprised observer distances of 300 m (410 D,); most laboratory-scale studies are restricted by chamber walls that extend only a few meters from the source region.…”