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
Crackle Noise in Heated Supersonic JetsCrackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shocklike compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et ai, 2011, "The Effect of Chevrons on Crackle-Engine and Scale Model Results," Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these ohseiyations, it was conjectured that crackle is associated with coherent large scale fiow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fullyunstructured meshes.
Objective The study sought to describe the development, implementation, and requirements of laboratory information system (LIS) functionality to manage test ordering, registration, sample flow, and result reporting during the coronavirus disease 2019 (COVID-19) pandemic. Materials and Methods Our large (>12 000 000 tests/y) academic hospital laboratory is the Belgian National Reference Center for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing. We have performed a moving total of >25 000 SARS-CoV-2 polymerase chain reaction tests in parallel to standard routine testing since the start of the outbreak. A LIS implementation team dedicated to develop tools to remove the bottlenecks, primarily situated in the pre- and postanalytical phases, was established early in the crisis. Results We outline the design, implementation, and requirements of LIS functionality related to managing increased test demand during the COVID-19 crisis, including tools for test ordering, standardized order sets integrated into a computerized provider order entry module, notifications on shipping requirements, automated triaging based on digital metadata forms, and the establishment of databases with contact details of other laboratories and primary care physicians to enable automated reporting. We also describe our approach to data mining and reporting of actionable daily summary statistics to governing bodies and other policymakers. Conclusions Rapidly developed, agile extendable LIS functionality and its meaningful use alleviates the administrative burden on laboratory personnel and improves turnaround time of SARS-CoV-2 testing. It will be important to maintain an environment that is conducive for the rapid adoption of meaningful LIS tools after the COVID-19 crisis.
A research program was carried out to explore the effects of nozzle trailing-edge modi cations on the ow structure, jet mixing with the ambient air, and jet noise of a rectangular supersonic jet. Nozzles with one modi ed trailing edge were used with the intention of enhancing mixing and reducing noise. The modi cations were simple cutouts in the plane of the nozzle wall and acted to induce large-scale streamwise vortices. A rectangular jet, with a design Mach number of 2 and with various trailing edges, was examined using optical diagnostics and noise measurements in ow regimes ranging from moderately overexpanded M j = 1:5 to moderately underexpanded M j = 2:5. The results indicated that in nonideally expanded ow regimes, one could generate pairs of streamwise vortices of various strength and sign and that the mixing could be signi cantly enhanced. The results also indicated that the modi cations could eliminate or at least substantially reduce screech noise and could signi cantly decrease the overall far-eld sound pressure level in the nonideally expanded ow regimes. In the ideally expanded ow regime, the trailing-edge modi cations did not seem to induce streamwise vortices and, thus, did not have a substantial effect on the jet mixing or noise.
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