A parametric study of the noise radiated by the flow around multiple bodies: direct noise computation of the influence of the separating distance in rod-airfoil flow configurations

Abstract

The sound radiated by an airfoil in the wake of a rod is predicted by means of compressible large-eddy (LES) simulation. The LES strategy is based on high-order spectral-like numerical methods to allow the direct noise calculation of the sound sources. Owing to the complexity of the geometry, an overset grid approach is implemented in order to tackle with turbulent flows around multiple solid bodies. First, the aerodynamic data as well as the acoustic far-field are thoroughly compared to the experimental data of Jacob et al. [J. Theoret. Comput. Fluid Dyn., 19(3), 2005] in order to demonstrate the accuracy of the present simulation. Then a parametric study of the influence of separating rod-airfoil distance on the flow regimes and on the acoustic radiation is performed.

Experimental study of vortex–structure interaction noise radiated from rod–airfoil configurations

“…7 that there is a critical value of L/D ¼3.3 below which the overall SPL undergoes a sharp decrease of more than 30 dB. This critical ratio is in close agreement with the numerical finding of Berland et al (2011) where the ratio is 3.5 in the case of one diameter rod. This phenomenon suggests that at this situation the embedded airfoil may work as a splitter plate which prevents the formation of the rod Karman vortices (Spiteri et al, 2008;You et al, 1998), contributing to the drastic noise reduction.…”

“…Giesler and Sarradj (2009) demonstrated experimentally the effect of the rod diameter and the streamwise gap on the broadband noise of high frequencies far above the vortex shedding frequency. In addition, Berland et al (2011) performed DNC on the influence of the streamwise gap. The current paper follows Giesler and Sarradj (2009) by investigating further the effects of these two parameters on the radiated noise, not only at the broadband frequencies but also at the vortex shedding frequency, especially the influence of the gap/diameter ratio.…”

“…These investigations presented results which were in agreement with the experiments, but the applied numerical methods decouple the aerodynamic and acoustic fields, which makes it difficult to determine the details of the flow physics that are responsible for the noise generation. Recently, Berland et al (2010Berland et al ( , 2011 performed a direct noise calculation (DNC), based on compressible LES, to predict the sound radiation from the rod-airfoil configuration. The DNC method does not require any modelling of the sound sources and computes aerodynamic and acoustic fluctuations within a single run.…”

Numerical Investigation on Vortex‐Structure Interaction Generating Aerodynamic Noises for Rod‐Airfoil Models

“…It can be seen that the vortices in the opposite direction alternately interact with the airfoil and the strength of the vortices is becoming weaker and weaker with the increase of the downstream distance from the cylinder. At the same time, the broken vortex phenomenon induces the fluctuating pressures on the airfoil surface [24]. Above all, in the unsteady flow, due to the interaction between the upstream vortex and the airfoil, the wing leading edge becomes the main noise source in the rod-airfoil model as Jacob's experiment [19] and other numerical simulation results [24].…”

“…The density, interference domain, and the strength of the vortices are all bigger than those of the cylinder. The aerodynamic noise level is also expected to be larger than the cylinder rod-airfoil model according to the connections between the vortex and sound radiation [7,24]. Figure 22 presents the frequency spectrum of the sound pressure level.…”