The present invention relates to centrifugal fluid machines such as a pump or compressor and, more particularly, relates to a centrifugal fluid machine in which noise and pressure pulsation may be suitably abated.
A flow distribution which is not uniform in the peripheral direction occurs at the outlet of an impeller due to the thickness of a vane and secondary flow or boundary layer occurring between the vanes. Such nonuniform pulsating flow interferes with the leading edge of the vanes of a diffuser or a volute tongue, resulting in a periodical pressure pulsation and causing a noise. In some cases, such pressure pulsation vibrates the diffuser and furthermore vibrates a casing or an outer casing outside thereof through a fitting portion, whereby the vibration is propagated into the air surrounding the pump to cause a noise.
In a centrifugal pump as disclosed in Zulzer Technical Review Vol. 62 No.1 (1980) PP.24-26, the noise is reduced by varying radius of the trailing edge of vanes of the impeller or the peripheral position of the trailing edge of the vanes in the direction of axis of rotation. Further, in an electric fan as disclosed in Japanese Patent Laid-Open Publication No. 51-91006, a pressure increasing section and a noise abatement section (the noise abatement section being the portion where the peripheral position of a volute tongue is varied in the direction of axis of rotation) are formed on the volute wall of a volute casing and the peripheral distance of the noise abatement section is made substantially equal to the peripheral distance between the trailing edges of the vanes that are next to each other in the impeller, so that the flow from the impeller does not impact the volute tongue all at once. In this manner, a shift in phase in the direction of axis of rotation occurs in the interference between the flow and the volute tongue, whereby the periodical pressure pulsation is mitigated to lead to an abatement of the noise.
In the above prior art, however, there has been a problem that, when radius of the trailing edge of the vane of the impeller is varied in the direction of axis of rotation, the head or the efficiency thereof is reduced due to the fact that the ratio between radius of the trailing edge of the impeller vane and radius of the leading edge of the diffuser vane or radius of the volute tongue is varied in the direction of axis of rotation. Further, when the outer radius of the main shroud and the front shroud of the impeller are different from each other in association with the fact that the trailing edge radius of the impeller vane is varied in the direction of axis of rotation, an axial thrust occurs due to difference between the projected areas of the main shroud and the front shroud in the direction of axis of rotation. In the case where the peripheral position of the trailing edge of the impeller vane is varied in the direction of axis of rotation, although the peripheral distance between the trailing edge of the impeller vane and the leading edge of the diffuser vane or the volute tongue is varied, amount of such change has not been optimized. In the case where the peripheral position of the volute tongue is varied in the direction of axis of rotation and amount in such change is substantially equal to the peripheral distance between the trailing edges of the impeller vanes which are next to each other, the portion for effecting the pressure recovery in the volute casing becomes shorter where a sufficient pressure recovery cannot be obtained.
An object of the present invention is to provide a centrifugal fluid machine in which reduction in head and efficiency or occurrence of an axial thrust is controlled while noise and pressure pulsation are abated.
In the case of a diffuser pump, the above object may be achieved such that the trailing edge radius of the impeller vane and the leading edge radius of the diffuser vane are increased or decreased monotonously in the direction of axis of rotation and inclinations on a meridional plane of the trailing edge of the impeller and the leading edge of the diffuser are in the same orientation.
Alternatively, it may be achieved such that, of the trailing edge of the impeller vane, radius at the center in the direction of axis of rotation is made larger than radius at the two ends in the direction of axis of rotation and, of the leading edge of the diffuser vane, radius at the center in the direction of axis of rotation is made larger than radius at the two ends in the direction of axis of rotation.
Alternatively, it may be achieved such that, of the trailing edge of the impeller vane, radius at the center in the direction of axis of rotation is made smaller than radius at the two ends in the direction of axis of rotation and, of the leading edge of the diffuser vane, radius at the center in the direction of axis of rotation is made smaller than radius at the two ends in the direction of axis of rotation.
Alternatively, it may be achieved such that the trailing edge radius of the impeller vane and the leading edge radius of the diffuser vane are varied in the direction of axis of rotation and the ratio between the trailing edge radius of the impeller vane and the leading edge radius of the diffuser vane is made constant in the direction of axis of rotation.
Alternatively, it may be achieved such that the peripheral distance between the trailing edge of the impeller vane and the leading edge of the diffuser vane is varied in the direction of axis of rotation and difference between the maximum value and the minimum value of the peripheral distance between the trailing edge of the impeller vane and the leading edge of the diffuser vane is made equal to the peripheral distance between the trailing edges of the vanes next to each other in the impeller or to a part obtained by equally dividing that by an integer.
Alternatively, it may be achieved such that, when the leading edge of the diffuser vane and the trailing edge of the impeller vane are projected onto a circular cylindrical development of the diffuser leading edge, the leading edge and the trailing edge of the vanes are perpendicular to each other on the circular cylindrical development.
In the case of a volute pump, the above object may be achieved such that the trailing edge radius of the impeller vane and radius of the volute tongue of the volute casing are increased or decreased monotonously in the direction of axis of rotation and inclinations on a meridional plane of the trailing edge of the impeller vane and the volute tongue are set in the same orientation.
Alternatively, it may be achieved such that, of the trailing edge of the impeller vane, radius at the center in the direction of axis of rotation is made larger than radius at the two ends in the direction of axis of rotation and, of the volute tongue of the volute casing, radius at the center in the direction of axis of rotation is made larger than radius at the two ends in the direction of axis of rotation.
Alternatively, it may be achieved such that, of the trailing edge of the impeller vane, radius at the center in the direction of axis of rotation is made smaller than radius at the two ends in the direction of axis of rotation and, of the volute tongue of the volute casing, radius at the center in the direction of axis of rotation is made smaller than radius at the two ends in the direction of axis of rotation.
Alternatively, it may be achieved such that the trailing edge radius of the impeller vane and the radius of the volute tongue of the volute casing are varied in the direction of axis of rotation and the ratio between the trailing edge radius of the impeller vane and the radius of the volute tongue is made constant in the direction of axis of rotation.
Alternatively, it may be achieved such that the peripheral position of the trailing edge of the impeller vane is varied in the direction of axis of rotation and difference between the maximum value and the minimum value of the peripheral distance between the trailing edge of the impeller vane and the volute tongue is made equal to the peripheral distance between trailing edges of the vanes that are next to each other in the impeller or to a part obtained by equally dividing that by an integer.
Alternatively, it may be achieved such that, when the volute tongue of the volute casing and the trailing edge of the impeller vane are projected onto a circular cylindrical development of the volute tongue, the volute tongue and the trailing edge of the vane are perpendicular to each other on the circular cylindrical development.
In the case of a multistage centrifugal fluid machine, the above object may be achieved such that, for at least two impellers of the impellers of the respective stages each constituted by a main shroud, a front shroud and vanes, the trailing edge radius of the vane is varied in the direction of axis of rotation and the main shroud and the front shroud are formed into different radiuses; of the impellers of which the main shroud and the front shroud are formed into different radiuses, the outer radius of the main shroud of at least one impeller is made larger than the front shroud thereof and the main shroud of the remaining impellers is made smaller than the front shroud thereof.
Alternatively it may be achieved such that, for an even number of impellers of the impellers of the respective stages each constituted by a main shroud, a front shroud and vanes, the trailing edge radius of the vane is varied in the direction of axis of rotation and the main shroud and the front shroud are formed into different radiuses of the impellers of which the main shroud and the front shroud are formed into different radiuses, the main shroud of one half of the impellers is made larger than the front shroud thereof and the main shroud of the remaining half of the impellers is made smaller than the front shroud thereof.