|Title of Invention
A BI-DIRECTIONAL FLOW IMPULSE TURBINE WITH UNI-DIRECTIONAL ROTATION
|The bi-directional flow impulse turbine with uni-directional rotation according to this invention comprises a turbine rotor with blades housed in a casing the turbine being symmetrical about the mid rotational plane and the blades being symmetrical about the rotor plane. the two rows of fixed guide vanes, disposed with in the casing,on either side of the rotor and symmetrical with respect to the mid rotational plane both the rows of said guide vanes having the same nozzle cascade geometry, the cascade outlet directions being axial.
This invention relates to a bi-directional flow impulse turbine with uni-directional rotation.
In wave energy conversion devices, such as, the osci llating water column (OWC) devices, pneumatic power is available in the form of bi-directional or osci llating air-flow at the sea-wave frequency. An air turbine which is capabl e of operating in such an air flow while running in the same directiony all the time, which is also known as a self-rectifying turbine, is required for converting this pneumatic power into mechanical shaft power. The OWC device can be a fixed structure or a floating structure off shore.
Known to the art is the Wells Turbine which rotates in a Binglt direction in a bi-directional air flow- Thi© turbine has a rotor of several symmetrical airfoil bladesi set around a hub such that the blad chords life in the plane of rotation. The air flow generated by the OWC enters/leaves the turbine axially.
Unidirectional flow impulse turbines are designed such that the row of guide vanes upstream of the
rotor have the geometry to act as nozzle, accelerating and turning the flow which then impinges on the rotor blades. The row of guide vanes downstream of the rotor have the geometry to act as diffuser whereby the flow is turned back to nearly axial direction and some pressure recovery also occurs-
Known also to the art is the impulse turbine with self-pitch-controlled guide vanes which achieves bi-directional operation by changing the geometry of the guide vanes on either side of the rotor depending on the direction of air-flow. The guide vanes are all pivoted and are free to rotate in their bearings. However, each guide vane is linked to a guide vane opposite to it across the turbine rotor. There are mechanical stops to limit the guide vanes rotation to pre-set angles and normally the vanes orient themselves in one of these two extreme angles. Depending on the direction of air-flow, the two rows of guide vanes take up the correct orientations to act as nozzle and diffuser- Whenever, the flow direction reverses, the vanes rotate (f1ip)automatically
under the action of aero-dynamic moment® acting on them ®o that the vane row which was diffuser become® nozzle (in geometry) and vice versa. Thus the turbine rotate® in a single direction in bidirectional or oscillatory flow and produces shaft power-
The draw back® of the Well® turbine are that its efficiency drops to nearly zero when a certain air-flow rate i» exceeded due to stalling of it® blade foil®. The ratio of maximum flow rate to minimum flow rate is small. Additionally, it has poor starting characteristic® due to it® low torque at low speeds.
The impulse turbine with self-pitch controlled guide vanes does not have the above drawbacks of the Well® turbine. Efficiency does not drop to near zero at high flow rates as in the ca®e of the Well® turbine. It ha® good efficiency over a wide range of flow coefficients which in turn means a wide range of flow rate® for a given turbine rpm. It has very high stalled torque and so has excellent starting characteristics.
The drawback©, however, are that it has a complex construction. It requires a spherical hub and Contoured edges of the vanes which are more difficult to manufacture. Other than the turbine rotor, It has a large number of moving part®, namely, the guide vane© and bearings. The vanes and their supports have to be designed to withstand the flow due to the largest wave. As the turbine has many moving linkages in guide vane assemblies it requires more maintenance effort, especially in marine environment.
On the other hand, the turbine proposed herein is simple in construction and has the rotor as the only moving part, even though its efficiency is lower. It is reliable and requires very little maintenance. It has wide operating flow rates and excel lent starting characteristics. Its optimum flow coefficient is higher and so will be run at an rpm lower than that of the other two known types of turbihes referred to above.
The turbine proposed herein can be used for power generation near the shore with a fixed OWC. It
can be used in OWC plants which are floating offshore . It can be used for generation of power for navigational and other types of buoys deployed in the sea. Some of these buoys use solar cells for electricity generation- During nights and bad weather, sunshine is not available, whereas wave energy is available most of the time.
The bi-directional flow impulse turbine with unidirectional rotation, according to this invention, comprises a turbine rotor wi th blades housed in a casing, the turbine being symmetrical about the mid-rotational plane and the blades being symmetrical about the mid-rotor plane; two rows of fixed guide vanes, disposed within the casing, on either side of the rotor and symmetrical wi th respect to the mid-rotational plane, both rows of said guide vanes having the same nozzle cascade geometry, the cascade outlet directions being axial.
This invention will now be described with reference to the accompanying drawings which illustrate, by way of example, one of possible
embodifments of the turbine proposed herein,
Fig . 1 i 1 lust rating a diagram of one of possible
embodiments of the turbine proposed herein
Fig-2 11 lustrating a separate view of the rotor
blades, guide vanes and the rotor of the said
In the drawings, F indicates the bi-directional
The turbine has a rotor R with blades B housed in a casing C. H is the rotor hub and D the direction of rotation of the rotor.
The turbine is symmetrical about the mid-rotational plane and the blades are symmetrical about the mid-rotor plane-There are two rows of fixed guide vanes B, disposed within the casing, on either side of the rotor R and symmetrical with respect to the mid-rotational plane. Both rows of said guide vanes have the same nozzle cascade geometry, the cascade outlet directions being axial.
Flow entering the turbine axially is turned and accelerated in the guide vane® B upstream of the rotor. The air then strike® the rotor blades and passes through them applying torque on the rotor R, due to rat© of change of angular momentum. The flow leaving the rotor goes through the downstream guide vanes with axial outlet angle. The guide vane geometry is not optimal for acting as downstream diffuser.
The terms and expressions in this specification are of description and not of limitation, since the turbine proposed herein is not confined to the embodiment described and i1lustrated herein, by way of example, but it is understood that various other embodiments thereof are possible wlthout departing from the scope and ambit of this invention.
1. A bi-directional flow impulse turbine with uni
directional rotation comprising a turbine rotor
with blades housed in a casing, the turbine being
symmetrical about the mid-rotational plane and the
blades being symmetrical about the mid-rotor
plane; two rows of fixed guide vanes, disposed
within the casing, on either side of the rotor
and symmetrical with respect to the mid-rotational
plane, both rows of said guide vanes having the
same nozzle cascade geometry, the cascade outlet
directions being axial.
2. A bi-directional flow Impulse turbine with uni
directional rotation substantially as herein
described with reference to, and as i1 lustrated
in, the accompanying drawings.
Dated this the 20th day of July 1998 National Institute of Ocean Technology
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|NATIONAL INSTITUTE OF OCEAN TECHNOLOGY
|IC & SR BUILDING, IIT CAMPUS, CHNNAI 600036,
|PCT International Classification Number
|F16 H 41/00
|PCT International Application Number
|PCT International Filing date