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Aeroacoustic Characteristics of a Synchronized Fluidic Oscillator
Flow, Turbulence and Combustion ( IF 2.0 ) Pub Date : 2020-06-28 , DOI: 10.1007/s10494-020-00193-3 Elias Sundström , Mehmet N. Tomac
Flow, Turbulence and Combustion ( IF 2.0 ) Pub Date : 2020-06-28 , DOI: 10.1007/s10494-020-00193-3 Elias Sundström , Mehmet N. Tomac
A new opposite facing oscillator pair is presented where shared feedback channels enable synchronized sweeping of the exiting jets. The design has no moving parts and the oscillator pair is composed in a back-to-back configuration. The synchronized operation generates a near-field acoustic tonality and the objective is to determine the emitted directivity. The acoustic generation mechanisms were determined using compressible large eddy simulations, which was validated with hot-wire and microphone measurements. Different Reynolds number ( Re ) conditions up to 21,250 were analyzed for a synchronized oscillation with Strouhal number ( St ) of order 0.01. Dominant acoustic sources emerging during synchronized sweep oscillation were classified by the interpretation of directivity patterns for a selected flow rate. The near-field directivity pattern could be decomposed as a periodic signal consisting of one acoustic mode with a dipole-like pattern, showing two major lobes associated with the jet sweeping oscillation frequency: one acoustic monopole-like directivity for the first overtone; and dipole-like directivity with two lobes for the second harmonic. It is shown that the acoustic sources are generated by the synchronized pressure oscillation of the exiting jets. The vortical structures inside the fluidic oscillator interact with the non-slip walls. These manipulate the curvature of the central jet and causes an unsteady loading towards the discharge. The new fluidic oscillator design gives synchronized exiting sweeping jets and a large flow length scale near-field directivity pattern. These features give feedback type fluidic oscillators a wider application range.
更新日期：2020-06-28
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