Water turbine or water pump

Details Water turbine or water pump Water turbine or water pump

1997-11-13

2001-07-03

Lopez, F. Daniel (Department: 3745)

Rotary kinetic fluid motors or pumps

Selectively adjustable vane or working fluid control means

Upstream of runner

C415S208200, C416S237000

Reexamination Certificate

active

06254338

ABSTRACT:

DESCRIPTION
The invention concerns a water turbine or pump having a rotor and a stator which are provided with rotor blades and stator blades respectively.
Water turbines of the Kaplan or Francis type and water pumps of a corresponding configuration are frequently adversely affected in function by leaves and foliage, grass, pieces and scraps of plastic material, lumps or the like which are entrained in the water. Those items which are entrained in the water stick to the leading or afflux edges of the rotor blades and the stator blades and therefore considerably interfere with the flow around the cross-sectional profile of those blades. As a result the level of efficiency in part falls considerably and, in the case of water pumps, that, together with reductions in the through-flow rate, results in a sharp rise in the power draw. Those disadvantageous effects make themselves particularly felt in relation to water turbines and water pumps of the specified kind, which are of medium or small size and in which consequently not only the trailing edges but also the leading edges, in the form of a profile nose, are comparatively sharp. For, those relatively sharp leading edges also already retain entrained fibres or leaves and foliage of relatively small extent.
In order to reduce or entirely eliminate the tendency of the blades to retain solid body impurities and contaminants entrained by the water, it is already known for the leading edges of the rotor and/or stator blades to be of a rearwardly curved configuration, as viewed in the direction of flow (EP-A 475 920). That arrangement, unlike the leading edges which generally extend substantially perpendicularly to the direction of flow, is intended to set the leading edges in relation to the flow direction in such a way that flow components are effective which are also parallel to the leading edge and foreign bodies which are thereby held fast thereby are swept away. In the case of blades which are non-adjustable in relation to the flow, as is the case for example with Francis turbines, a suitable configuration is relatively easy to implement. Particularly in the case of rotor blades which are adjustable in dependence on flow, as is the case with Kaplan turbines and water pumps of a corresponding configuration however the proposed rearward curvature gives rise to structural and operational disadvantages. Thus for example adjustability of the rotor blades of a Kaplan turbine about a blade axis which extends substantially radially with respect to the axis of rotation, and the variation which is caused thereby in the position of the blade tip in relation to the surrounding housing, require adaptation such that in the region of adjustment of the rotating blades, the housing is of a part-toric shape. That design configuration is intended to minimise the gap losses at the blade tip in all adjustment positions of the rotor blades. That toric configuration of the housing is at its smallest when the leading and trailing edges of the rotor blades, like also the adjustment axis, extend substantially radially with respect to the axis of rotation. Due to the proposed rearward curvature of the rotor blades however, if the substantially radial adjustment axis is retained, the consequence involved is a considerable pivotal travel of the blade tip, which results in a corresponding increase in the size of the toric part of the housing. Corresponding rearward pivotal displacement of the displacement axis such that it is substantially matched in terms of its position to the configuration of the leading edge requires re-designing of the corresponding drive in the hub and involves a considerably larger demand for space. In addition the blades due to the rearward curvature become corresponding longer and accordingly the level of expenditure on material and the loading acting on the blades become greater.
Furthermore, for the purposes of affording the desired self-cleaning action for water turbines and pumps, it has also already been proposed that, in addition to the regular rotor and/or stator blades, special cleaning blades with a rearwardly curved leading edge should be provided and disposed upstream of the regular blades (EP-A 512 190). That is intended to provide that solid body impurities entrained by the flow are already engaged by the cleaning blades before they reach the leading edges of the regular blades, and are laterally deflected by virtue of the rearward curvature of the leading edges. The provision of additional cleaning blades however requires a considerable level of expenditure and complication and cannot be implemented in turbines and pumps with adjustable blades without a considerable limitation in terms of the adjustment travel.
Therefore the object of the invention is so to design the blades of water turbines or pumps that the desired self-cleaning effect can be achieved even in relation to water turbines or pumps with adjustable blades, in particular rotor blades, without involving a high level of expense.
In accordance with the invention that is achieved in that the leading edges and the trailing edges at least of the rotor blades form a bend projecting in opposite relationship to the direction of flow.
The bend in the leading edge which occurs for example at the longitudinal center of the leading edge provides that the leading edge is curved or inclined rearwardly with respect to the flow starting from the bend towards both ends of the blade. The rearward inclination or curvature which occurs adjoining the bend, relative to the direction of flow, is compensated for by virtue of the fact that, from the one end of the blade, for example from the blade fixing to the rotor hub, the leading edge projects increasingly in opposite relationship to the flow direction. Accordingly the position of the two blade ends relative to each other is not changed or it is immaterially changed, with respect to the corresponding relative position of the blade ends of conventional turbines or pumps with leading edges which extend substantially perpendicularly to the flow direction.
As in addition the trailing edge has a bend in parallel relationship with the leading edge, the flow forces which are effective at the blade profile are not changed. For, the blade cross-sections can be imagined as infinitesimally thin lamellae which, starting from the one blade end, are increasingly displaced relative to each other in opposite relationship to the flow direction and, from the bend, are again displaced increasingly with the flow direction.
The leading and trailing edges can extend in a straight or curved shape in order to form the bend which occurs in the longitudinal configuration thereof. The angle with which the leading and trailing edges deviate from the otherwise usual orientation which is substantially perpendicular to the flow direction should be so great that flow forces acting on the foreign bodies which impinge on the leading edges are to be expected to be sufficient to sweep them away. It is desirably between 10° and 30°. In addition the angles at which the parts of the leading edge, which extend at both sides of the bend, are oriented with respect to the flow direction can be different. The endeavour however is to provide a corresponding angular configuration and position of the bend, which is matched thereto, in the longitudinal configuration of the leading edge, such that the relative position of the two blade ends, particularly in the case of adjustable rotor blades, does not change or changes only immaterially, in comparison with conventional blades.


REFERENCES:
patent: 1614872 (1927-01-01), Callahan
patent: 1907466 (1933-05-01), Terry
patent: 1929100 (1933-10-01), Moody
patent: 2663193 (1953-12-01), Keast

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