AN EXPERIMENTAL-BASED METHOD FOR ESTIMATING FAR-FIELD ACOUSTICS GENERATED BY A TURBULENT WALL JET

Noise generation via turbulent-flow interactions is a multifaceted problem that appears in many instances, from flow over bodies to jet flows found in circulation-control airfoils. The work presented here centers on an investigation of the noise generation due to a turbulent wall jet that operates at a moderate Reynolds number based on nozzle height of 25,500. A multistage, experimental-based method is demonstrated which utilizes spatially-resolved velocity field data obtained from Particle Image Velocimetry (PIV) and temporally-resolved fluctuating surface pressure measurements. The PIV snapshots and surface pressure measurements have been acquired synchronously to allow for correlations between the quantities to be leveraged in a Stochastic Estimation procedure. The spatially-resolved information obtained in PIV was decomposed using the snapshot Proper Orthogonal Decomposition (POD) to obtain a set of spatially-dependent basis functions and time-dependent scalar expansion coefficients. The modified-Stochastic Estimation is used in this work to estimate the time-dependent POD coefficients based on their relationship with the surface pressure measurements. When the estimated POD expansion coefficients are combined with the spatially-resolved POD modes, an estimated velocity field is obtained at a temporal resolution dictated by the fluctuating surface pressure measurements. With a sufficiently resolved velocity field series, Poisson's equation is solved for the fluctuating pressure field with the measured surface pressure used as boundary conditions in discrete locations in addition to the pressure gradient calculated by the Navier-Stokes equation at the other domain boundaries. This pressure field in turn is used as source in an acoustic analogy estimate of the far-field acoustics. Specifically in this work, Curle's acoustic analogy is employed, and the resulting quadrupole and dipole terms are investigated to further understand the acoustics of the turbulent wall jet. By treating the rigid wall as a passive reflector of perturbations caused by turbulent fluctuations and not an acoustic source, estimates of the far-field acoustics are found to match the Sound Pressure Level of direct far-field measurements.