CENTRIFUGAL TYPE BLOWER

PROBLEM TO BE SOLVED: To reduce noise in frequencies of a wide band by providing a plurality of ribs for each of a plurality of vanes over its pressure surface subjected to positive pressure in a place close to its end part in the outer side in the radial direction wherein the ribs are arranged in parallel at prescribed intervals while each one is prescribed in thickness, length and height, and is lengthwise directed in the flow direction. SOLUTION: A plurality of ribs 7 are provided at prescribed intervals in parallel with the length L direction of each vane 4 at its rear peripheral part for a plurality of the vanes 4 provided for an impeller. Each rib 7 may be provided only for the positive pressure side, or in order to effectively suppress noise, each rib may be provided for both the positive and negative pressure sides of each vane 4. Since vortexes as noise sources in a wide range are mainly developed within the velocity boundary layer of each vane 4, the height of each rib it to be basically determined based on the velocity boundary layer, and it is normally equal to or more than 2mm but less than 3mm. In addition, the spanwisw length of each rib 7, that is, each interval between the adjacent ribs 7 in the width H direction of each vane 4 is to be equal to or more than 10mm but less than 20mm, and its length is nearly equal to an interval between the ribs.