This study investigates the aerodynamic noise generated and radiated from a standard squareback body with various inclined side-view mirrors using a hybrid computational aeroacoustics method based on a stress-blended eddy simulation coupled with the Ffowcs-Williams and Hawkings acoustic analogy. The results indicate that in the absence of the side-view mirror, the idealized A-pillar is identified as the subsequent major contributor to the overall noise radiated from the vehicle body, and the coefficient of drag decreases by approximately 13.3% despite a minimal change in the projected frontal area. However, the behavior of the drag coefficient becomes nonlinear and highly dependent on the complex flow features, including the vortex shedding patterns and the interaction between the flow and side surface of the body, with increasing mirror inclination angle. In contrast, the radiated noise exhibits a constant decrease as the mirror inclination angle (θ) increases to 32°. Additionally, when the side-view mirror is considered as the sole source, the noise radiated is minimal for an inclination angle of 16°, and a further increase in inclination angle has no significant reduction on the noise radiated but alters the overall drag coefficient of the vehicle. These findings have practical implications for the design of side-view mirrors to reduce aerodynamic noise in automotive applications and highlight the complex tradeoffs between noise reduction and changes in the drag coefficient that must be considered in such designs.
A large eddy simulation (LES) was applied to predict the unsteady flow in a low-speed axial-flow fan assembly subjected to a highly “turbulent” inflow that is generated by a turbulence grid placed upstream of the impeller. The dynamic Smagorinsky model (DSM) was used as the subgrid scale (SGS) model. A streamwise-upwind finite element method (FEM) with second-order accuracy in both time and space was applied as the discretization method together with a multi-frame of reference dynamic overset grid in order to take into account the effects of the blade-wake interactions. Based on a simple algebraic acoustical model for axial flow fans, the radiated sound power was also predicted by using the computed fluctuations in the blade force. The predicted turbulence intensity and its length scale downstream of the turbulence grid quantitatively agree with the experimental data measured by a hot-wire anemometry. The response of the blade to the inflow turbulence is also well predicted by the present LES in terms of the surface pressure fluctuations near the leading edge of the blade and the resulting sound power level. However, as soon as the effects of the turbulent boundary layer on the blades become important, the prediction tends to become inaccurate.
Acoustics 08 Paris
7041A generic fan assembly consisting of a low pressure axial impeller including an optional turbulence generator is investigated. The flow field is simulated with different state-of-the-art unsteady computational fluid dynamic methods. All results are compared with each other and with hot wire flow velocity and surface pressure measurements. From the numerical data, the relevant dipole sound sources, i.e. the unsteady forces on the fan blades are derived. A free field formulation in the time domain (acoustical analogy by FFOWCS WILLIAMS and HAWKINGS), and a boundary element formulation in the frequency domain (SYSNOISE ® ) are employed to predict the radiated sound field based on the numerical source data. The acoustical results are compared and contrasted with measurements.
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