Multi-modal noise generation in low Mach number orifice plates: an experimental investigation
Résumé
Abstract. An experimental campaign on aerodynamic noise generation by orifice plates in rectangular ducts for low Mach number flows is carried. The test plant allows for the measurement of the total emitted acoustic power both upstream and downstream of the orifice plates for varying mass flow rates through the 2N-Port method. A modal decomposition for the first eight propagating higher-order acoustic modes is also performed. Keeping the free flow area and the plates’ thickness constant, the tests allowed for a study of the influence of the number of circular orifices on the generated acoustic power as well as its modal composition. It is found that the orifices’ number does not influence the overall pressure drop caused by the presence of the obstacle. The generated noise on the contrary is greatly affected by such a parameter both for the plane-wave frequency range and especially so in the multi-modal one.