A turbine rotor for a flow meter comprises a cylindrical rotor
disk having a rotor axis, a plurality of rotor vanes extending radially
from the rotor disk and a flat surface between the bases of each
of the vanes. This construction permits the efficient start-up of
the turbine rotor at flows of low viscosity.
What is claimed is:
1. A turbine rotor for flow meter comprising a cylindrical rotor
disk having a rotor axis, a plurality of rotor vanes extending radially
from said cylindrical rotor disk, at an angle of inclination .beta.
with said rotor axis, a flat surface between each of said rotor
vanes wherein each flat surface abuts a vane on each side forming
lines of abutment, said lines of abutment being parallel.
2. The turbine rotor of claim 1 wherein said rotor vanes are flat
3. The turbine rotor of claim 1 wherein the line normal to each
flat surface located at an equal distance from a frontal surface
of said rotor disk and extending from the central point of said
flat surface intersect at the same point along said rotor axis.
4. The turbine rotor of claim 1 wherein line normals pass through
the center of gravity of said flat plates and intersect at the same
point along said rotor axis.
5. The turbine rotor of claim 3 wherein said frontal surfaces
6. The turbine rotor of claim 1 wherein said angle of inclination
.beta. is between about 20.degree. and 30.degree..
7. The turbine rotor of claim 6 wherein .beta. is 25.degree..
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a turbine rotor for a flow meter wherein
the turbine rotor is arranged in a flow channel of the measuring
housing. The turbine rotor has specially designed blades and intermediate
plates and is positioned such that its axis is in the direction
of the flow. The flow meter is also equipped with an inductive pulse
2. Background of the Prior Art
Flow meters of this type are known per se and belong to the group
of the intermediate volume counters operating on the principle of
the so-called Woltmann impeller wheel counter and being particularly
suitable for the accurate measurement of the instantaneous volume
flow of fluids. A tukrbine rotor with a low mass centeringly located
in a tubular body is exposed to flow in the axial direction with
the medium to be measured impacting the turbine disk in the form
of a quasi laminar flow after having been quieted by means of flow
rectifiers. The rpm of the turbine disk is proportional to the mean
flow velocity and thus corresponds over a broad range to the volume
The rpm of the turbine disk is preferably taken off with a low
reaction force through the non-magnetic tubular body by means of
an inductive transducer. The number of pulses per unit time is proportional
to the instantaneous volume flow, while even in the case of the
minimum volume flow, the rpm of the turbine disk is not affected
by the inductive pulse takeoff. However, hydraulic losses are dependent
on viscosity and are functions of the Reynolds number, respectively.
By selecting high quality, low friction bearing materials and by
reducing the impeller mass, efforts have been made to keep the braking
torque as low as possible in order to preserve a maximum effect,
i.e., a broad measuring range of the counter or expansion of the
measuring range. This affects the characteristic of the error curve.
Such measures, however, largely depend on the angle of the blades
to the axis of the turbine disk and on the number of blades, whereby
the circumferential velocity of the impeller wheel is also affected.
Attempts to make the known turbine flow meters into an accurately
operating measuring instrument have led over the course of time
to improvements concerning the configuration of the impellers.
There are known configurations with two different slopes, for example,
wherein a steeper slope is used in the forward part of the disk
than in the rear part. This results in the fact that in the case
of small flow volumes, rpm ranges are attained whereby the lower
limit of the measuring range may be lowered. In order, however,
to avoid reaching excessively high rpm ranges leading to increased
wear, the rear part of the impeller disk is given with a less steep
slope, thereby providing for the necessary equalization of velocity.
The design of an impeller wheel with two different slopes is very
expensive to manufacture with the further disadvantage that an impeller
wheel of this type is not suitable for extremely broad measuring
A further known configuration of Woltmann wheels is based on a
design wherein six vanes have full diameters, while another six
vanes are shorter, i.e. having approximately one-half of their height.
Such a configuration is known as the so-called "stepped wheel".
The vanes therein are flat. By means of the intermediate vanes,
the formation of boundary layers on the vanes may be enhanced in
the case of low flow rates. Vanes on the outside are thereby stressed
higher which renders the counter more sensitive. The lower limit
of the measuring range can thus be reduced.
Such a measure is again expensive in view of the manufacturing
costs of the rotor disk.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the coefficient
of sliding friction is always less than the coefficient of static
friction in turbines. This relationship may be taken into consideration
with respect to the startup behavior of the turbine rotors. In other
words, a body set into motion by impact or a force acting in the
form of a pulse will require the introduction of a lesser force
than a body exposed to a continuously increasing force.
It is an object of the invention, therefore, to provide a configuration
of a turbine rotor whereby the static friction of a stationary rotor
is overcome at a very low velocity of the medium in order to expand
the measuring range in the direction of small flows. In addition
to other effects, forces appearing in the form of pulses are especially
suitable for the purpose. Pulses may may be generated in keeping
with the invention so that corresponding effects are obtained on
the stationary rotor.
This and other objects of the invention are attained by constructing
the turbine rotor of a flow meter having an induction pulse pickup
such that the bottom curves of the rotor disk between the vanes
are flat and form straight bottom lines that are parallel to each
other and with the adjacent vane surfaces. As the result of this
construction, the edges of the bottom surfaces on the upstream and
downstream side are no longer joined flush with the inflow and outflow
shapes, but triangular surfaces are created on the frontal sides
of the rotor disk, when viewed in the axial direction of the latter,
so that inflow and outflow edges are formed on the frontal surfaces
of the rotor disk. Vortices are generated in an irregular sequence
on the outflow edges, transferring pulse-like forces to the rotor
disk sufficient to overcome the static friction of the stationary
rotor disk. In cooperation with the inclination of the vanes, a
force component in generated in the case of their exposure to flow
in the direction of the circumference of the rotor disk, thereby
exerting a rotating force. Together with the forces appearing in
the form of pulses, the static friction of the rotor disk is overcome
even with very low flow velocities so that the measuring range is
expanded in the direction of the flows.
In a further embodiment of the invention, the surface normals located
at an identical distance from a frontal surface of the rotor disk
and standing on the centerlines extending in the flow direction
of the bottom surfaces intersect at one point of the rotor axis
of the rotor disk.
By means of this measure, the effective separation edges may be
varied such that the effect desired may be adjusted.
It is advantageous to have the surface normals that pass through
the center of gravity of all bottom surfaces intersect the axis
of the rotor disk at a single point.
In this embodiment, the separation edges on the two frontal sides
of the rotor disk are of equal size.
The frontal surfaces of the rotor disk are preferably flat which
is advantageous not only in view of the vortex formation desired,
but also for the manufacture of the rotor disk.
The bottom lines includes an angle of inclination .beta. with the
rotor axis of 20.degree. to 30.degree.. In a particularly advantageous
embodiment of the invention, the angle of inclination .beta. is
25.degree.. By means of this measure, adequate forces are generated
even in the case of extremely low flow velocities of the medium
to be applied immediately following the overcoming of the static
friction in order to effect a rotating motion.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will become more apparent with the aid of figures
representing the embodiments. In the drawings:
FIG. 1 shows a longitudinal section through a flow meter of the
measuring turbine type;
FIG. 2 illustrates a sector shaped segment of a rotor disk in an
FIG. 3 represents a rotor disk with the vanes shown in part only,
FIG. 4 illustrates the characteristic error curve according to
the present invention compared with the error curve of a corresponding
measuring instrument 25 according to the state of the art.
FIG. 1 shows a measuring turbine in a longitudinal section approximately
in its actual size. The measuring housing 14 surrounds a round flow
channel 15 and is equipped on the input side with an inlet 16 and
on the discharge side with an outlet 17 and discharge connector.
The inlet and outlet connectors are both equipped with threads.
The arrow 13 indicates the direction of flow of the flow medium
to be measured. Immediately following the inlet connection, a flow
rectifier 18 is located in the flow channel 15. The flow rectifier
comprises six baffle plates in the embodiment exemplified. Each
baffle plate is fastened to a ring 30 on the inlet side and simultaneously
serves as the holder for the rotor axle 2. In order to reduce the
formation of vortices, a flow form 19 precedes the rotor axle 2.
Further flow forms 20 21 and 22 are located in front and after
the rotor disk 4 and at the outlet end of the axle 2. The flow form
20 has a configuration, such that the fluid flowing against the
rotor disk is directed into the range of the rotor blades. The flow
form 21 is followed immediately by a further baffle arrangement
23 also serving to rectify the flow.
Bore holes 26 and 27 are present in the housing 14 to receive suitable
pressure and temperature transducers. These holes may be closed
off by means of the caps 28 and 29. The openings of the transducer
bores are located in the inlet area of the flow rectifiers 18 and
23 so that they have no appreciable effect on the turbine rotor
The housing wall 14 of the flow channel 15 has a bore 24 arranged
opposite the turbine rotor 4. An inductive measuring detector 25
(also referred to as an inductive pulse pickup) is located in the
bore 24. The depth of insertion of inductive measuring detector
25 is variable.
FIG. 2 shows a sector shaped segment of a rotor disk 4 through
its center wherein the bottom surfaces 3 located between the vanes
1 are flat. The bottom surfaces form straight bottom lines 5 and
6 parallel to each other with the adjacent vane surfaces 8 and 9.
The surface normals 7 passing through the center of gravity of
all of the bottom surfaces 3 intersect the axis 2 of the rotor disk
4 at a single point. The frontal surfaces 10 of the rotor disk 4
are flat as may be seen clearly in FIG. 1. Similarly, the angle
of inclination .beta. included between the axis 2 of the rotor disk
4 and the bottom lines 5 and 6 of the vane surfaces may be seen
in FIG. 1.
FIG. 4 shows the characteristic error curve (solid line) compared
with the corresponding error curve of a flow meter according to
the state of the art (broken line).
As clearly shown by the configuration of the curve, the measuring
curve begins for example at an error of -1% with a flow volume of
18 liter per minute. This actual measured value reflects one embodiment
of the invention. The curve rises very steeply and attains its maximum
with only a slight increase of the flow volume to a point equal
the value also obtained with the forms of embodiment of rotor disks
according to the state of the art.
As is readily seen by the application of the measure according
to the invention, the initial point of use of the flow meter may
be shifted toward lower flow volumes so that a significant expansion
of the measuring range is obtained.
A further advantage of the present invention consists of the simplified
manufacturing of the rotor disks as milling may be effected with
a single setting of the milling tool. This saves a series of further
work steps, resulting in an appreciable reduction of overall costs.
The specification and drawings set forth preferred embodiments
of the invention. It should be noted, however, that the invention
is not limited to those specific embodiments and methods specifically
disclosed, but extend instead to all embodiments, substitute and
equivalent constructions falling within the scope of the invention
as defined by the claims.