جستجوی مقالات مرتبط با کلیدواژه « ffowcs williams » در نشریات گروه « مکانیک »

This study carries out computational aeroacoustic calculations around the tip region of the CART II wind turbine blade. Additionally, two modified tip designs, namely; tip O and tip R, are further investigated to determine how the geometry of the tip region affects the noise emission characteristics of the wind turbine. The study focuses on the tip vortex noise mechanism using hybrid computational aeroacoustic to tackle the issue of the enormous computational power required for direct noise simulation. Improved Delayed Detached Eddy Simulation (IDDES) technique is used to calculate the instantaneous turbulent flow field near the sound source region, and the noise prediction in far-field is performed using the Ffowcs Williams and Hawking’s (FW-H) acoustic analogy. The method visualizes the flow field near the blades’ tip, assisting researchers to have an accurate understanding of aerodynamically induced noise mechanisms in that highly complex flow region, thus being able to modify tip design in a way that contributes to lower overall noise emission.  The results for the outboard section of the CART II wind turbine’s blade are validated with experimental data. Broadband noise sources such as turbulent-boundary-layer trailing-edge (TBL-TE) noise and the tip vortex noise mechanisms are investigated for the base case as well as tip O and tip R. The results show that the overall sound pressure level (OASPL) and the generated torque of tip R and tip O, are 2.0 %, 5.0 % and 0.8 %, 2.2 % lower than the base case, respectively.

Rotating cylinders have wide applications in different areas, especially the aerodynamic area. However, the acoustic behaviors of these components have not been widely studied. The generating noise from a spinning cylinder is mainly due to the detached vortices from the leeward of the body. In this study, the large eddy simulation technique is used to simulate the flow field over a three-dimensional cylinder. In the following, the Ffowcs Williams and Hawkings equation is used to estimate the noise at the specified locations using the oscillating pressure components on the cylinder wall. The acoustic behavior of both stationary and rotating cylinders are studied. Results show that the acoustic behaviors of cylinders rotating with smaller frequencies (up to f=16f0, where f0 is the dominant detaching frequency of vortices on a stationary cylinder) are nearly the same. However, at higher rotational frequencies (24f0) where vortices are omitted, OASPL of the generated noise is reduced considerably (about 20 dB at different angles with constant radial positions, r=26D, at mid-span plane). On the other hand, when the rotational frequency is increased over this limit, the pressure oscillation on the wall becomes significant and the OASPL approaches higher values.