Acoustic viscous boundary layer beyond laminar regime: Particle Image Velocimetry measurements
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International Journal of Heat and Fluid Flow
The current study reports an experimental investigation of flow regimes for acoustically oscillating flows in the near-wall region of a resonator. Particle Image Velocimetry (PIV) is used to measure axial and transverse velocity components inside an empty square resonator over the acoustic cycle for a wide range of Reynolds numbers and at a high Womersley number. The measurements are compared with LDV measurements in a circular duct. Good agreement between the PIV and LDV measurements is observed. The measured transverse distribution of the axial velocity agrees well with the Stokes boundary layer expectations up to Reynolds number (based on acoustic velocity and viscous boundary layer depth) of 240. At higher Reynolds numbers, the measured velocity distribution deviates from the theoretical expectations, suggesting a change of regime at Reynolds number around 240. To assert the critical Reynolds number, the turbulence intensities and Reynolds stress are estimated. At Reynolds number of 272, an increase in the value of the Reynolds stress is observed at the edge of the viscous penetration depth which is regarded as an indication for changing the flow regime. To better qualify the high amplitude acoustic flow, the spectrum of the turbulent kinetic energy and evolution of the integral length scale over the acoustic cycle are investigated. The decay of turbulent kinetic energy with the wavenumber complies with the universal slope (-5/3). The integral length scale increases during the deceleration stage and decreases at the beginning of the acceleration stage.
Ramadan, Islam and Ibrahim, Abdelmaged and Bailliet, Hélène and Abdel-Rahman, Ehab, Acoustic Viscous Boundary Layer Beyond Laminar Regime: Particle Image Velocimetry Measurements. Available at SSRN: https://ssrn.com/abstract=4047935 or http://dx.doi.org/10.2139/ssrn.4047935