| 摘要 |
PROBLEM TO BE SOLVED: To improve P-Q characteristic, and realize a W noise, by forming an annular wall having a clearance from the blade end of a fan, forming in this annular wall, a slit through which the inner and peripheral surfaces of the annular wall are communicated to a part opposed to the blade end, and setting the width of the clearance of this slit so as to satisfy the condition of a specific formula. SOLUTION: An annular wall 2 surrounding the circumference of an axial flow fan 1, is formed in a manner that annular plates 71 -75 are laminated by sandwiching spacers 8 among them, and slits 6 are formed among the adjacent annular plates out of the annular plates 71 -75 . The width W of clearances among the slits 6 is set to satisfy a condition of the formula (ν: kinematic viscosity of air, V: circumferential speed of blade end, Rec ; critical Raynolds number). By the set of the width W of these clearances, an air flow led to flow into from the slits 6 toward an inner side is turned into a laminar flow, a leakage vortex led to flow into from a positive pressure side to a back pressure side at the blade end is suppressed, the air flow may not be drifted away on a back pressure, surface, a P-Q characteristic can be improved, and a noise can be reduced. |
