BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of a conventional centrifugal impeller employing airfoil blades of signal-blade design.
FIG. 2A is a top view of an impeller structure according to a preferred embodiment of the invention.
FIG. 2B is a cross sectional view of FIG. 2A.
FIG. 3 and FIG. 4 are schematic diagrams depicting a blade structure of the invention.
FIG. 5 is a cross sectional view of a centrifugal fan device according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several preferable embodiments cooperating with detailed description are presented as the follows.
Please refer to FIG. 2A and FIG. 2B, which are top view and a cross sectional view of an impeller structure according to a preferred embodiment of the invention. The impeller structure 2 is comprised of: a disc 20; and a plurality of blade structures 21, each being arranged on the disc 20 and connected to each other by a front cap 22; wherein, each blade structure 21 further comprises: a first blade 210; and a second blade 211, arranged at a circumferential length away from a side of the first blade 210 while radially overlapping with the radial of the first blade 210 by a overlap area. In this preferred embodiment, the plural blade structures are arranged on the disc 20 in an annular manner.
Please refer to FIG. 3 and FIG. 4, which are schematic diagrams depicting a blade structure of the invention. The blade structure of the invention is improved over the prior-art single airfoil blade, that is, it is a blade structure of two-blade design, referring as the first blade 210 and the second blade 211. Similarly, a pressure surface 2100 and a suction surface 2103 can be identified and classified on the first blade 210 while a pressure surface 2110 and a suction surface 2113 can be identified and classified on the second blade 211. As seen in FIG. 3, the relative position of the first and the second blades is that: the second blade 211 is arranged at a circumferential length away from a side of the first blade 210 by enabling the leading edge 2111 of the second blade's 211 suction surface 2113 to be positioned in the proximity of the trailing edge 2102 of the first blade's 210 pressure surface 2100 while radially overlapping with the radial of the first blade by a specific overlap area for forming a gap passage 212 functioning as a nozzle. As a fluidic is flowing through and shooting out of the gap passage 212, not only the growth of the boundary layer on the suction surfaces 2103 of the first blade 210 is interrupted, but also as the fluidic with high kinetic energy is mixing with the low-kinetic fluidic flowing on the suction surface 2113 of the second blade 211, the thickness of the boundary layer is reduced while the separation point is delayed and thus separation can be prevented. Therefore, not only the separation loss and the missing loss are reduced, but also the fan noise is reduced since the flow field is more uniform as the generation of vortex is improved. To sum up, the uniformity of the flow field of the impeller is improved by the improvement of the blade structure thereof for the growth of the boundary layers on the suction surfaces of the blades are interrupted.
In a preferred aspect, the ratio of the radial blade length of the second blade, referring as Cr, over the radial blade length of the first blade, referring as Cf, is in the range of 0.8˜2.0, in which Cr is defined as the difference between a radius of a circle 93, defining by the center of the disc 20 and the trailing edge 2112 of the second blade 211, and a radius of a circle 91, defining by the center of the disc 20 and the leading edge 2111 of the second blade 211, and Cf is defined as the difference between a radius of a circle 92, defining by the center of the disc 20 and the trailing edge 2102 of the first blade 210, and a radius of a circle 90, defining by the center of the disc 20 and the leading edge 2101 of the first blade 210. Moreover, the ratio of a pitch defining the overlapping area, referring as Rol, over the radial blade length of the first blade (Cf), i.e. Rol/Cf, is in the range of 0˜0.2, in which Rol is defined as the difference between the radius of the circle 92 and the radius of the circle 91.
In addition, as seen in FIG. 4, the ratio of the circumferential length, referring as t and being defined as a distance between a leading edge 2111 of the second blade 211 and a trailing edge 2102 of the first blade 210, over the radial distance between trailing edges 2102, 2102a of two adjacent first blades 210, 210a, referring as s, i.e. t/s, is in the range of 0.05˜0.15.
Please refer to FIG. 5, which is a cross sectional view of a centrifugal fan device according to the present invention. The centrifugal fan device 3 is comprised of a volute shell 30, a centrifugal impeller structure 31 and a shaft 32. The volute shell 30 has a fluidic outlet and a fluidic inlet 301. The centrifugal impeller structure 31 is arranged inside the volute shell 30, that is further comprised of a disc 310 having a plurality of blade structures formed thereon, wherein, each blade structure further comprises: a first blade 311; and a second blade 312, arranged at a circumferential length away from a side of the first blade 311 while radially overlapping with the radial of the first blade by a overlap area. It is noted that the relative position of the first and the second blade is similar to that shown in FIG. 2 and thus is not described further herein. The shaft 32 has an end connecting to the center of disc 310 and another end connecting to a driving apparatus 33, whereas the driving apparatus 33 is used for proving power to the shaft 32 and bringing along the disc 310 to rotate, such that the impeller structure 31 is activated.
As a fluidic 95 is flowing into the centrifugal fan device 3 through the fluidic inlet 301, the shaft 32 is driven to rotate by the driving apparatus 33 for bringing along the centrifugal impeller structure 31 rotate and thus the energy of the flowing fluidic is raised. Thereafter, the flowing fluidic is discharge from the outlet of the impeller structure 31 and enters the volute shell 30 to be decelerated and expanded, and eventually, discharged from the outlet of the volute shell 30. It is noted that, not only the blade design of the impeller structure 31 can enable the growth of the boundary layer on the suction surfaces of the first blade to be interrupted, but also as the fluidic with high kinetic energy is mixing with the low-kinetic fluidic flowing on the suction surface of the second blade, the thickness of the boundary layer is reduced while the separation point is delayed and thus separation can be prevented. Therefore, not only the separation loss and the missing loss are reduced, but also the fan noise of the centrifugal fan device 3 is reduced since the flow field is more uniform as the generation of vortex is improved. To sum up, the uniformity of the flow field of the centrifugal fan device 3 is improved by the improvement of the uniformity of flow field and the generation of vortex.
To sum up, by the use of the impeller structure of the invention, not only the growth of the boundary layers on the suction surfaces of front blades are interrupted, but also as the fluidic with high kinetic energy is mixing with the low-kinetic fluidic flowing on the suction surfaces of rear blades, the thickness of the boundary layer is reduced while the separation point is delayed and thus separation can be prevented.
While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
Patent Application
20080050228
