Identification and modeling of the acoustic impedance of helmholtz resonators submitted to a grazing flow

We present here an application of inverse and updating method to analyse the effects of grazing flow on the acoustic impedance at the entry of a branched Helmholtz resonator. We are mainly interested in the inlet and the exhaust system of thermodynamic machines (engines, pumps, cleaning system, air conditioning system, turbo machines). Updating method uses a continuous transfer matrix formulation and consist in the identification of the acoustic pressure and flow at the entry of the resonator. This allows to compute the entry impedance of the resonator. We test twenty five resonators composed by a circular neck and a circular cavity for five flow rate having Mach number varying between 0 and 0,2. We show the effects of a turbulent grazing flow on the resistance and the effective neck length of the resonator.