Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural distributing means immediately upstream of runner
Patent
1994-03-17
1995-11-28
Look, Edward K.
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural distributing means immediately upstream of runner
415194, F01D 102
Patent
active
054702003
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The following invention relates to a guide vane arrangement for axial fans, intended to convert the rotational component in the gas flow velocity after passage through the impeller into a substantially axial velocity, the arrangement including a ring of guide vanes disposed downstream of the fan and in spaced relationship therewith.
BACKGROUND ART
The gas flow downstream of the impeller of an axial fan normally rotates. The rotational energy can be translated into useful energy by a guide vane arrangement on the outlet side of the fan, this arrangement converting the rotational velocity to an axial velocity component. The pressure is raised in this way, and the efficiency of the fan increases. Normally, however, the sound level also increases at the same time.
The sound from a fan comprises tonal components, i.e. tones with discrete frequencies and a wide band noise with a continuous frequency spectrum. Considerable efforts have been made primarily to lower the tonal components, by a suitable arrangement and embodiment of guide vanes on the output side of the fan.
It is accordingly a general understanding that the noise generated decreases with increasing distance between the impeller and guide vanes, see M. J. Benzakein, J. Acoust. Soc. Am. 51 (1972), 1427-1438 and W. Neise, Proc. INTER-NOISE 1988, pp 767-776. It has been found, however, this is not always applicable.
A guide vane is described in the Swedish patent 8802136-5, which has improved aerodynamic and acoustic properties.
It has also been found earlier that a non-uniform distribution of the guide vanes in the ring of guide vanes can give rise to certain acoustic improvements, although it has been found that large deviations from a uniform distribution of the guide vanes give rise to aerodynamic problems.
It is also known that certain acoustic characteristics can be improved by a portion being cut out from alternate guide vanes in their the forward portions.
FIG. 1 illustrates how the strength in an individual tone can be reduced by displacing the guide vanes in the circumferential direction of the guide vane ring. It will also be seen from the same figure that the noise at higher frequencies over about 500 Hz also increases at the same time. The measurement has been made for a fan R.P.M. of n=970 and a displacement of alternate guide vanes of .beta.=10.degree. and .beta.=0.degree..
DISCLOSURE OF THE INVENTION
The object of the present invention is to lower individual, disturbing tones in the fan sound, as well as lower the general noise level in a simple way.
The first-mentioned object is achieved with a guide vane ring of the kind mentioned in the introduction, and with characteristics disclosed hereinbelow 1.
The second object is achieved by a further development of the inventive guide vane arrangement, in which alternate guide vanes are axially displaced relative the remaining ones, so that alternate guide vanes are at a first axial distance from the fan, and the remainder at a second axial distance, simultaneously as the guide vanes are non-uniformly distributed in the guide vane ring circumference. Preferably, alternate guide vanes are displaced in the circumferential direction relative to the remaining guide vanes with a constant displacement so that the distance in the circumferential direction between juxtaposed guide vanes alternates between two given values. This arrangement reduces both individual tones and the general wide band noise from the fan. In addition, this combination of axial displacement and circumferential displacement of the guide vanes provides improved efficiency of the fan, compared with the case using a guide vane arrangement with only axial displacement of the guide vanes, or only rotation of the vanes in the circumferential direction.
By the combination of measures according to this further development of the apparatus in accordance with the invention, there are achieved highly important advantages, both with respect to acoustics and efficiency, considerably exceeding the effects achieved by t
REFERENCES:
patent: 821347 (1906-05-01), Elling
patent: 2839239 (1958-06-01), Stalker
patent: 3883264 (1975-05-01), Rao
patent: 5152661 (1992-10-01), Sheets
patent: 5246339 (1993-09-01), Bengtsson
Nilsson Borje
Nilsson Patrick
Tupov Vladimir
ABB Flakt Aktiebolag
Look Edward K.
Sgantzos Mark
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