Aeroacoustic Characteristics of a Synchronized Fluidic Oscillator
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Aeroacoustic Characteristics of a Synchronized Fluidic Oscillator Elias Sundström1 · Mehmet N. Tomac2 Received: 18 February 2020 / Accepted: 22 June 2020 © The Author(s) 2020
Abstract 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. Keywords Synchronized fluidic oscillator pair · Hot-wire and microphone measurements · Large eddy simulation
* Elias Sundström [email protected] 1
Department of Otolaryngology‑Head and Neck Surgery, University of Cincinnati, Cincinnati, OH 45267, USA
2
Aerospace Research Center, The Ohio State University, 2300 W. Case Rd, Columbus, OH 43235, USA
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Flow, Turbulence and Combustion
1 Introduction The fluidic oscillator is a device commonly used to generate an oscillating jet (when supplied with a pressurized fluid) without the use of moving parts. The oscillations occur due to the internal fluid dynamics in the unit and have been used in a broad range of applications, for example, noise mitigation (Raman and Raghu 2004; Raman and Raghu 2000; Shigeta et al. 2009), combustion control (Guyot et al. 2009), and separation control (Metka and Gregory 2015; Seele et al. 2009). Depending on the design, size, and feed rate of the oscillator, the oscillation frequency can be adjusted from the order of 10 Hz to 22 kHz (Gregory et al. 2007). An overview describing the historical evolution of fluid oscillators is presented by Gregory and Tomac (2013).
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