Aeroacoustic noise calculations of non-compact bodies with permeable boundaries

A hybrid computational aeroacoustic method with permeable boundary is developed to evaluate non-compact noise induced by low Mach number flow over arbitrarily shaped bodies. Based on Lighthill’s equation and the boundary element method, the unified integral equations are established in which the integral boundary surrounding the objects can be selected arbitrarily. Validation studies are developed for noise induced by two-dimensional NACA0012 airfoil and three-dimensional circular cylinder. For NACA0012 airfoil, the directivity patterns of calculated noise with different permeable boundaries agree well with Howe’s analytical solution for trailing edge model. The acoustic noise generated by circular cylinder has a good agreement with Revell’s experimental data and FW-H equation. It demonstrates that the noise predicted by different permeable boundary is as accurate as that calculated by the body surface.

Acoustic Behavior Prediction and Analysis of Resonators in the Presence of Low Mach Number Flow

The frequency-domain linearized Navier–Stokes equations (LNSEs) are used to describe the sound field of Helmholtz resonators and concentric perforated tube resonators in the presence of low Mach number flow. The numerical procedure of LNSEs method is performed in three steps, computational fluid dynamics (CFD) calculation, data transfer and acoustics calculation. The transmission loss predictions of the resonators exhibit good agreement with measurements published in the literature. The results show that the low Mach number flow shifts the resonance frequencies of resonators and changes the acoustic attenuation behavior, which may be attributed to the change of acoustic impedance of the opening and orifices. In order to weaken the effect of flow on the resonance frequency, the modified configurations of resonators are proposed by using the conical tubes to reduce the flow velocity passing the opening and orifices. Numerical results demonstrated that the influence of flow velocity on the resonance frequency of the modified resonators is less sensitive than the original configurations.

Reduction of Aeroacoustic Sound and Aerodynamic Drag using Porous Cover

The application of a porous media on square cylinders to reduce drag in cross-flow is an active research area. Be that as it may, the related stream incited sound in the encompassing flow likewise experiences decrease, an angle which has gotten less consideration. This paper exhibits a numerical strategy for coupled streamlined and aero acoustic estimations for low Mach number flow current pass a square cylinder with permeable cover. Computations are performed at a subcritical Re of 54,800 using URANS technique and FW-H acoustic analogy. The cylinder without porous cover is subjected to an incoming flow is considered for validation against measurements. A significant drag reduction and sound reduction is observed with the presence of the porous layer. Comparisons are made among the modified cylinder and its unmodified counterpart.