Effect of chevron count and penetration on the acoustic characteristics of chevron nozzles

Impact of chevron spacing and asymmetric distribution on supersonic jet acoustics and flow

“…Considering the relation of Tam et al [36] (shown below in Eq. (2)) this can be explained by a reduction of the average shock cell spacing and/or an increase in the convective velocity, though previous studies [12,51,44] indicate that the reduction in the shock spacing alone can account for the frequency increase:…”

“…Drastic modification of the jet cross-section was achieved by the investigated configurations, with both elliptic and triangular shapes attained downstream. Consequently, screech was nearly eliminated with reductions in the range of [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] dB depending on the operating condition. Analysis of the streamwise velocity indicated that both the mean shock spacing and strength were reduced resulting in an increase in the broadband shock associated noise spectral peak frequency and a reduction in the amplitude, respectively.…”

“…For example, of the above mentioned studies, Seiner et al [1] was the only group which did not employ 12 chevrons and only a single chevron configuration was investigated. Arrangement has been investigated in the past for chevrons applied to non-military style nozzles in both subsonic [9], and supersonic [10][11][12] jets. Bridges and Brown [9] found that periodic azimuthally spaced chevrons with asymmetric geometry were detrimental to subsonic noise reduction when compared to chevrons with symmetric geometry and identical penetration.…”

“…Additionally, due to a lack of azimuthal periodicity, an azimuthal sound field was measured which required operating condition dependent clocking (relative to the engine's pylon) for optimal noise reduction. Finally, Tide and Srinivasan [11,12] investigated the effect of chevron number and asymmetry on sonic nozzles. They found that increases in chevron number were beneficial, and chevron asymmetries improved noise reduction, in particular broadband shock associated noise (BSAN), compared to standard chevron configurations at specific azimuthal angles.…”

Towards the noise reduction of piezoelectrical-driven synthetic jet actuators

“…The chevron count and penetration is a primary factor in controlling the compromise between low-frequency reduction and high-frequency SPL augmentation. It has been proven experimentally 9 that a higher chevron count with a lower level of penetration and zero degree taper, yields the maximum noise reduction for low and medium nozzle pressure ratios. Specifically, a chevron nozzle with eight lobed chevrons reduces jet noise by 8 dB.…”