Experimental investigation of the noise reduction of a plug fan with leading-edge serrations

International audienc

Noise Reduction of a Centrifugal Plenum Fan with Leading Edge or Trailing Edge Serrations

Leading-edge or trailing-edge serrations have been used with some success as a noise-reduction technique applied to fixed airfoils in wind-tunnels. More recently, this technique has also been used on axial fans. A previous investigation by the authors also assessed the application of sinusoidal blade leading-edge serrations on a plug fan. ln this study, these previous results are re-evaluated and corrected. Furthermore, new research based on blade trailing-edge serrations is also presented. RANS simulations on a non-serrated baseline impeller have been performed to define an assumed optimum geometry of leading-edge serrations to reduce the noise. This geometry has been used as a reference to manufacture three impeller prototypes with various geometries of serrations defined by their amplitude and wavelength. Three impellers with trailing-edge serrations were also designed, based on design criteria for fixed airfoils. All these impellers had an iron-shaped geometry, deemed to be better than the more prevalent sawtooth or sinusoidal shape. All six prototypes have been tested in a reverberant room, where noise and air performance were measured simultaneously. For each impeller, six fan operating points were tested, and for each point, the sound levels in narrowband and one-third octave band were measured at the fan inlet and outlet. This allowed assessing the effectiveness of serrations at different operating points while checking their impact on the performance curve and fan efficiency. The results were then compared with the reference fan without serrations. Leading-edge serrations have yielded a mitigated sound power reduction (up to 1 dBA reduction in the overall sound power level) and only for some configurations. One of the impellers slightly reduced the noise at all the operating points, another did it at some of them and the third one increased the noise at most of the operating points. Trailing-edge serrations, on the other hand, reduced broadband noise for all operating points and impeller prototypes (an overall sound pressure decrease between 1 and 5 dBA). Leading-edge serrations reduce noise for low to mid frequencies but increase it over 1 kHz, whereas trailing-edge serrations reduce noise along the whole spectrum

Analytical prediction of the blade trailing edge broadband noise of a plug fan

International audienceAbstract This study presents a low-order broadband noise prediction tool for centrifugal plug fans, based on analytical models using inputs from CFD simulations. Firstly, the fan used as a reference in this investigation was tested in a double reverberant room where the aerodynamic performance and the acoustic signature were measured simultaneously. Secondly, CFD RANS simulations of the fan in the test rig were performed. The outcome of the simulations is then used to feed Amiet’s analytical broadband noise model, along with wall-pressure spectral and correlation length models. Amiet’s model has been transposed to a rotating blade, adapted to the geometry of the fan. Finally, the model predictions are compared with the measurements