WO1992015782A1

WO1992015782A1 - Apparatus for recovering kinetic energy in a free flowing water stream

Info

Publication number: WO1992015782A1
Application number: PCT/CA1991/000066
Authority: WO
Inventors: Jean-Marc Lalancette
Original assignee: Lalancette Jean Marc
Priority date: 1991-03-06
Filing date: 1991-03-06
Publication date: 1992-09-17

Abstract

The disclosure herein describes an apparatus for recovering kinetic energy in a free flowing water stream and converting it into useful energy; it comprises a body (22) immerged in a stream, the body defining a duct having an intake side (26) and a discharge side (27). The discharge side is equipped with a deflector (30) which flares outwardly for obstructing the flow of water around the duct to thereby create a negative pressure drag on water being impelled as it is being discharged from the duct. The deflectors flare outwardly at an angle varying from 75° to 160° as measured from the longitudinal axis of the duct.

Description

Apparatus for recovering kinetic energy in a free flowing water stream

FIELD OF THE INVENTION

The present invention relates to an apparatus for recovering kinetic energy in a free flowing water stream and converting it into useful energy.

BACKGROUND OF THE INVENTION

The recovery of useful energy from water streams is ancient. When an important water head is available, the impact or impulse of the water stream is used to produce useful work, such as with Pelton wheels. With lower water head, but generally with much larger water flow, a reaction configuration is found to be more efficient and is well exemplified by Francis turbines or similar designs.

Another aspect of this technology is found in equipments of small size, leading to easily handable units that can be carried by air or water to remote areas. In practice, the fractional recovery of power at a given site is not necessarily a drawback as long as the generation of power is sufficient for the local needs. Presently, in remote areas, internal combustion engines are used for the production of electrical power resulting, however, in very high cost due to the low efficiency of such machines and transportation of fuel. Alternate systems making use of the kinetic energy available in a free flowing stream without the assistance of auxiliary structures have been examined in different ways.

The paddle wheel, located on a floating barge with various types of intakes, has been the subject of several patents, although the water wheel by itself is probably the oldest water-activated machine known. The profile of the blades (US Patent 4,104,536, 1978), the mode of power transmission (Russian Patent, 153,883, 1963) and the type of water intake (U.S. Patent 4,436,480) have been objects of specific claims.

There has been adaptation of wind mill configurations to extraction of energy from free-flowing streams as exemplified by the Savonius rotor and the

Darrieus type vertical axis rotor (Technical Report,

National Research Council, Canada, March 1984) .

Another approach relates to translators or belt-like devices circulating at reduced speed along with the water current. Several patents dealing with such configurations concern mainly the mechanism of return of the belt (US Patent 3,927,330, 1975) or the floating system (German Patent 3,114,847, 1981). Oscillating or cyclic devices which are said to take advantage o* tides are also numerous and may be exemplified by Canadian Patent 1,132,436.

For various reasons related mainly to low efficiency, bulkiness and generally poor performances, these designs have not been retained as promising, axial flow devices being rated intrinsically superior from hydrodynamic considerations.

The oldest patent concerning an axial turbine in a free-flowing stream is attributed to McLaughlin (U.S. Patent 868,798, 1907) and deals with a floating screw anchored in a stream. Several other patents relate to machines using propellers or helix without external fairing or duct, these inventions dealing with supporting structures such as hydrofoils (Souczek, U.S. Patent 2,501,696,1950), shape of screw (Grugeaud, French Patent 2,457,989,1959) or anchoring technique (Bowley, U.S. Patent 4,383,182, 1983). A second type of patent based on axial flow devices includes a static duct around the rotating wheel. The duct can vary from a simple ring around the rotor (Corren et al, U.S. Patent 4,613,279, 1986) to more elaborate structures such as profiled intakes and discharges (Mouton, U.S. Patent 4,219,303, 1980 and Holliger, U.S. Patent 4,545,726, 1985). Particularly, Chappell et al, in U.S. Patent 4,258,271, 1981) describe a duct around the intake where the incoming stream is constricted ahead of the turbine, said duct being flared out at an angle from 35° to 75° on the discharge side.

The examination of this literature leads to the conclusion that substantial improvement of the performances of the rotating turbine is needed if the free-flowing water around the turbine is involved in promoting the operational conditions of the turbine.

OBJECTS AND STATEMENT OF THE INVENTION The present invention is therefore directed to a technique which allows recovery of energy from a stream without the major involvement of fixed structures such as dams, spillways and ducts. Such an arrangement allows to reclaim but a small fraction of the available energy at one given site; however, the cost of the operation is minimal due to a lack of major fixed structures and the environmental impact is reduced in comparison with the upheave generated by standard approaches.

One feature of the present invention is to make use of the free flowing water around the body of a turbine to create, by an appropriate profile of the body, a vacuum or suction on the discharge side in order to increase the speed of the water flowing through the turbine to a velocity higher than the speed of the free flowing water around the body. Wheels or towed screws are poor energy extractors when used without ducts as extractive apparatus in a moving stream because the water deflected by the solid surfaces of these machines has no place to go but sideways, interfering with the non-deflected part of the stream. The net result of this situation is that, because of turbulence and back-up pressure in front of the paddle or screw, there is a deflection of the stream sideways ahead of the screw or paddle and the effective speed of the stream, which hits the paddle or blade, has thus a speed reduced significantly when compared to the speed of the undisturbed stream. This point is well proven by the recommended practice with paddle wheels where a slip of 15% rather than the theoretical 50% is recommended precisely to avoid these losses induced by turbulence and back-up pressure. (Naval Architecture, Cecil H. Preabody, 4^th ed, 1917, John Wiley, page 438).

The mechanical considerations are to the effect that a reacting surface operating in a free flowing stream, either a paddle or a screw, is performing poorly because the impinging water has no place to go after being deflected by the reacting surface but against the free stream. This pile-up, or clogging effect, has the net result of a reduction of speed at the instant of energy exchange in the turbine. The present invention therefore pertains to a novel configuration of the turbine stator so as to facilitate the evacuation of the- stream as it is deflected by the reacting surface, thus providing a significant gain in terms of efficiency due to increase speed through the turbine at the instant of interaction of the accelerated stream with the turbine rotor.

The present invention is concerned with using a mobile reacting surface, such as the vanes of a turbine, upon which momentum of the incoming water is felt, thus allowing a transfer of energy to the surface by reaction. If the deflected stream has to compete with a wall of undeflected water as it leaves the reacting surface at an angle, the efficiency is poor. On the other hand, it is an object of the present invention to provide the structure holding the reacting mobile surface with a configuration so as to generate a positive pressure drag coefficient in front, or uptake side, of the reacting device and a negative drag coefficient in the back, or discharge side, of the reacting device. Under such circumstances, two major gains are experienced by the reacting machine. First, the apparent speed of the water stream in increased at the site of reaction by the pressure difference created between the intake and discharge sides of the reacting mechanism. Secondly, the creation of a negative pressure drag coefficient behind the holding structure is equivalent to generate a space where the deflected stream is able to discharge without inducing back pressure on the reacting surface. Under such conditions, much improved performances are noted for a given surface of reaction with a water stream.

The present invention therefore relates to an apparatus for recovering kinetic energy in a free flowing water stream and converting it into useful energy, which comprises: a body immerged in the stream; the body defining a longitudinal duct having an axis extending in the direction of the flow of water; the duct including an intake side at one end thereof and a discharge side at an opposite end thereof; means mounted at the discharge side impelling water flowing through the duct and converting kinetic energy of the water into mechanical energy; and deflector means flaring outwardly at the discharge side for obstructing the flow of water around the duct to thereby create a negative pressure drag on impelled water; the deflector means defining a profile formed of one or more segmented surfaces, a line coincident with the outermost of said surfaces defining an angle from 75° to 160° as measured from the longitudinal axis of said duct.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an apparatus for recovering kinetic energy made in accordance with the present invention;

Figure 2 is a cross-sectional elevational view of the apparatus of figure 1 shown disposed in a free flowing water stream; Figure 3 is a schematic representation showing the various angular limits at the intake and at the discharge ends of the apparatus of the present invention; and

Figures 4 and 5 show various configurations at the intake and the discharge ends of the duct.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to figure 1, there is shown an apparatus for recovering kinetic energy, generally denoted 10, shown mounted on a platform 12 by means of a series of supporting element 14 and 16. An assembly, generally denoted 18, is also mounted to the platform by means of another supporting element 20; this assembly serves for collecting and converting the kinetic energy into other energy, such as mechanical and/or electrical energy. It will be understood that they are many ways in achieving this conversion and this assembly 18 does not form part of the present invention.

Figure 2 shows the apparatus disposed at the bottom of a free flowing stream. The apparatus 10 comprises a body 22 defining a longitudinal duct and having an axis extending in the direction of the flow of water as represented by arrows 24. The duct has an intake side 26 and a discharge side 27 at an opposite end thereof. At the discharge side, propeller means 28 are provided for impelling the water flowing through the duct and converting the kinetic energy of the water into mechanical energy. Also provided at the discharge side of the duct is a deflector 30 which flares outwardly and obstructs the flow of water circulating about the duct to thereby create a negative pressure drag on the impelled water. This flaring may consists of a single planar surface, such as illustrated in figures 1 and 2, or of a series of segments, each segment being angled to an adjacent surface. It may also consists of a curved (semi-hemispheric) surface, such as illustrated in figure 3, which, in fact, is a series of infinitesimal segmented surfaces. The beneficial effect of this pressure drag assistance on the speed of flow through the duct located in a free flowing stream has been examined with different configurations of ducts. The measurement of the speed through the duct is an evaluation of the available power at the outlet of the duct since it is well known that the extractable energy from a ducted water stream is proportional to the third power of its speed. Therefore, a gain in speed of the ducted stream, even if moderate, has a very substantial effect on the potential energy output of the system.

Various profiles are examined in figures 4 and

5. The legend in these two figures is as follows: α: angle of intake β : angle of last deflector segmented surface

V: speed of free flowing stream v_β: speed of ducted stream d: diameter of the duct D: overall diameter of deflector

1: overall length of the duct

In the drawings, four values of the angle of intake α are given: A, B, C and O while five values of deflector profiles are represented as 1, 6, 7, 8 and 9.

In the examples given hereinafter, the following values are: A = - 5° 1 = 75° 0 = 0° 6 = 90° B = +10° 7 = 135° C - +20° 8 = 135° 9 = 135°

Therefore, configuration A-l means an intake having an angle α of -5° and a deflector angle β of 75°.

Different ducts were placed in a free flowing stream of constant and known velocity. Experiments were conducted with ducts wherein the ratio of D/1 varied from 4 to 0.5. A too high D/1 ratio will create turbulent conditions at the intake inducing undesirable side effects; a too low D/1 ratio will generate an awkward apparatus difficult to anchor and cumbersome to handle in addition to generating functional losses in the somewhat lengthy duct.

Example 1:

Evaluation of the effect of the angle β of deflection. Configuration Angle β V v_a Power available

(m/s) (m/s) (V/v_a)³

A-l 75° 0.56 0.68 1.75

B-l 75° 0.56 0.66 1.60 C-l 75° 0.56 0.65 1.52

B-6 90° 0.56 0.71 2.00

0-6 90° 0.53 0.70 2.20

C-6 90° 0.53 0.63 1.79 A-9 135° 0. 57 1. 02 5 . 83

0-9 135° 0. 52 0. 97 6. 54

These results indicate that, as the angle of deflection increases, the gain of available power in the ducted stream increases rapidly.

Example 2:

Evaluation of the effect of the ratio of the diameter (D) of the deflector to the diameter (d) of the duct. Configuration V

(m/s)

0-7 0.51

0-8 0.50 0-9 0.52

A-8 0.50

A-9 0.57

C-8 0.56

C-9 0.41

These results indicate that a larger ratio D/d improves the speed gain in the duct and the available power, a ratio of « 4.5 or more being quite satisfactory.

Example 3:

Evaluation of the gain of speed by a given configuration of speed by a given configuration related to the speed of the free-flowing stream. Configuration

B-8 B-8 B-8 B-8 B-8 B-8 B-8

The conclusion from this series of results is to the effect that, as the speed of the free-flowing stream increases, the gain of speed in the duct increases.

Example 4:

Evaluation of the effect of the shape of the intake on the gain of speed in a given profile at a given speed of free-flowing stream.

Configuration v_a V v^V (m/s) (m/s)

A-9 0.45 0.69 1.55

0-9 0.45 0.68 1.51

B-9 0.45 0.65 1.46 This indicates that, in the range of intake opening (-5° to +15°) , the situation is equivalent.

From these results, it appears that the optimal profile is one which will give maximum pressure drag coefficient at the discharge side of the ducts. This is obtained by incorporation of the following considerations in the design: a) the intake must not disturb the flow pattern around the deflector. To that purpose, the value of a can vary from a slightly negative value (-5°) to +15° maximum;

b) the profile of the deflector at the rear of the device must insure maximum drag coefficient by means of a profile corresponding to an angle β of opening of a value between 75° and 160°, preferably 135°;

c) the D/d ratio can vary in a range of 2 to 6.

It will be readily understood by those familiar with the design of hydraulic machinery that these ratio will have to be adjusted in scaling up these results by application of dimensional analysis and hydraulic similitude to the new and larger configuration.

The design of the water wheel or turbine located at the discharge of the duct will be done in accordance with the rules of the art, taking advantage of the available water flow with increased velocity from the action of the duct.

Although the invention has been described above with respect with one specific form, it will be evident to a person skilled in the art that it may be modified and refined in various ways. More particularly, the configuration of the rotor which does not form part of the present invention may be different from that shown in the drawings. It is therefore wished to have it understood that the present invention should not be limited in scope, except by the terms of the following claims.

Claims

1. An apparatus for recovering kinetic energy in a free flowing water stream and converting it into useful energy, comprising: a body immerged in said stream; said body defining a longitudinal duct having an axis extending in the direction of the flow of water; said duct including an intake side at one end thereof and a discharge side at an opposite end thereof; means mounted at said discharge side impelling water flowing through said duct and converting kinetic energy of said water into mechanical energy; and deflector means flaring outwardly at said discharge side for obstructing the flow of water around said duct to thereby create a negative pressure drag on impelled water, said deflector means defining a profile formed of one or more segmented surfaces, a line coincident with the outermost of said surfaces defining an angle from 75° to 160° as measured from the longitudinal axis of said duct.

2. An apparatus as defined in claim 1, wherein said segmented surfaces are infinitesimal so as to define a curved profile and wherein said line is a tangent at the outer edge of said profile.

3. An apparatus as defined in claim 1, wherein said angle is about 135°.

4. An apparatus as defined in claim 1, 2 or 3, wherein said intake side of said duct has flaring walls having a low angle to facilitate water intake without disturbing the negative pressure drag at the discharge side.

5. An apparatus as defined in claim 4, wherein said low angle varies from a value of -5° to +15° as measured from the longitudinal axis of said duct.

6. An apparatus as defined in claim 1, 2, 3 or 5, wherein said duct has a cylindrical shape and said deflector means displays a circular outer edge; the diameter of said circular edge being from 2 to 6 times the diameter of the duct in the central region thereof.

7. An apparatus as defined in claim 6, wherein the ratio of the diameter of said circular edge in relation to the longitudinal length of the duct varies from 4 to 0.5.

8. An apparatus as defined in claim 1, 2, 3, 5 or 7, wherein said means mounted at said discharge side further includes means to convert said mechanical energy into electrical energy.

9. An apparatus as defined in claim 1, 2, 3, 5 or 7, wherein said means mounted at said discharge side consist of a rotatable impeller allowing substantial radial discharge of said impelled water.