Multiblade fans have been widely used for car air-conditioning systems because of their high flow rates and high pressure as compared to their size. These fans, however, cause a comparatively high noise level due to their high rotational speed and the complex flow pattern inside the blade passages. This paper concerns the pressure fluctuation on the blade surfaces and the flow pattern inside a multiblade fan for car air-conditioning systems. As uneven flow distribution between shroud and hub was found to cause a large pressure fluctuation on the blade surfaces, resulting in the generation of high-level turbulent noise.
