Jet Noise Reduction in Co-Flowing Jets with Finite Lip Thickness

Passive control for suppressing mixing noise from Co-Flowing Jets (CFJ) is presented in this study. The idea behind this is to reduce the convective Mach number of turbulent eddies that produce intense sound radiation. The present study analyses co-flowing jets with a bypass ratio of 6.3 and the primary nozzle lip thickness of 10 mm. The aim of the study is to find the jet noise level in finite lip thickness in co-flowing jets. CFJ with finite lip thickness forms a recirculation zone (in the near field). The secondary core and recirculation zone are shielding the primary core by reducing the jet noise. A single free jet with a diameter equal to that of a primary nozzle of co-flowing jet is also studied for comparison. The results show that co-flow jet with finite lip thickness of 10mm for various emission angles and the Overall Sound Pressure Level (OASPL) level gets reduced when compared with the single free jet.

Validation of a High-Order Large Eddy Simulation Solver for Acoustic Prediction of Supersonic Jet Flow

A high-order large eddy simulation (LES) code based on the flux reconstruction (FR) scheme is further developed for supersonic jet simulation. The FR scheme provides an efficient and easy-to-implement way to achieve high-order accuracy on an unstructured mesh. The order of accuracy and the shock capturing capability of the solver are validated with the isentropic Euler vortex and Sod’s shock tube problem. A heated under-expanded supersonic jet case from NASA’s Small Hot Jet Acoustic Rig (SHJAR) database is used for validation. The turbulence statistics along the nozzle centerline and lip-line are examined. We predict the acoustic radiation with the Ffowcs Williams and Hawkings method, which is integrated with our solver. The far-field acoustic predictions show reasonable agreement with the experimental measurement in the upstream and downstream directions, where the shock-associated noise and the large-scale turbulent mixing noise are dominant, respectively.

Acoustic analysis of starting jets in an anechoic chamber

<p>Explosive volcanic eruptions emanate complex acoustic signals. They<br>are influenced by several parameters, most of most of which are highly<br>unconstrained in volcanic setting.</p><p>We investigate the acoustics of starting jets analogous to<br>volcanic jets at high Mach numbers and with different nozzle<br>geometries, in a controlled environment. For the first time in<br>volcanic analog studies, an anechoic chamber is used to eliminate<br>contamination of the signals by reflections from any wall or<br>obstacle.  The analysis concentrates on the identification of the<br>principal jet noise components including: compression waves, vortex<br>ring noise, turbulent jet mixing noise,  broadband shock noise and<br>screech. We employed a shock tube apparatus and signals were recorded<br>using a microphone array.  Employing wavelet analysis, we have<br>identified the noise sources in both time- and frequency-space.</p><p>We have identified the principal sound sources of the jet in<br>time-frequency space and have analyzed their behaviour with respect to<br>changes in pressure ratio $p/p_\infty$ ,non-dimensional mass supply<br>L/D and exit-to-throat area ratio.</p><p>We find that at higher pressure ratios the peak frequency of the<br>broadband shock noise is noticeably lower whereas the amplitude is<br>higher. The non-dimensional mass supply controls whether a jet forms<br>and its blowing duration and maximum velocity. The nozzle geometry has<br>a markable effect on delay of the shock-shear layer-vortex ring<br>interaction with respect to the compression wave.</p><p>Changes in parameters of the starting jet leave a clear and<br>interpretable trace in the observed sound pattern. This quantitative<br>parametrisation of these effects is essential for utilizing these<br>findings as well as field observations for the solution of the inverse<br>problem in the lab and in nature.</p><p> </p>