FORM 2
THE PATENT ACT  1970
(39 OF 1970)
AND
THE PATENTS RULES  2003

COMPLETE SPECIFICATION
(See Section 10; rule 13)

A FLOW GUIDE ELEMENT FOR STEAM TURBINES

TRIVENI TURBINE LTD
an indian company 
of 12A  Peenya Industrial Area 
Banglore-560058.

The following specification particularly describes the present invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
The present invention relates to the field of fluid flow maneuvering elements. Particularly  the present invention relates to steam flow maneuvering element in steam turbines.

BACKGROUND OF THE INVENTION:
Steam turbines comprises a plurality of blades typically configured in three modules viz High pressure module (HP)  Intermediate pressure module (IP) and Low pressure module (LP).

Flow guide elements are positioned at different locations of the steam turbine and serve different purposes. Typically  flow guide elements (diffusers) are positioned at the exit of the last stage turbine blades or in between the HP module and IP module or IP module and LP module or HP module and LP module (i.e.  in turbines where there is no IP module).

Figure 1 illustrates a divergent diffuser located at the exit of the last stage turbine blades.
The divergent diffuser 12 located at the exit of the last stage turbine blades produces a decelerating steam flow. This decelerating steam flow causes a decrease in kinetic energy of the steam and an increase in pressure  the net effect being creation of minimum pressure zones at the inlet of the diffuser. As a result  the steam exhausting from the last stage blades enters in to the low pressure zone of the diffuser  thereby resulting in the increase of the velocity of the steam flowing through the last stage blades and thus increasing the amount of energy available for the turbine to perform work.

Figure 2 illustrates a conventional flow guide element located between HP module and IP module of a steam turbine. The HP module is of reaction type and the IP module is of impulse type. The primary function of the flow guide element 14 is to facilitate in the smooth flow of the steam without formation of vortices and turbulences etc between the HP module and IP module and thereby minimizing the flow separation losses and increasing the efficiency of the turbine.

Figure 3 illustrates a sector of analytical model of the flow guide element of figure 2 to which boundary conditions are applied and simulation is run. The boundary conditions are applied based on the location of the flow guide element with respect to the modules of the steam turbine. The stationary and rotating walls are selected and are generally indicated by reference numerals S and R respectively. The speed of the rotor is 5625 rpm.
The portions of Inlet  Tip Seal Inlet  Outlet  Labyrinth Seal outlet are selected based on the mating interface of the flow guide element with the modules of the steam turbine and are generally indicated by reference numerals I  TI  O and LO respectively.

The boundary conditions applied to the analytical model and the operating conditions at which the simulation is performed are tabulated in Table 1:

Boundary Condition Design Case
At Inlet (I)
Total Pressure 1550.70 KPa
Total Temperature 285.75 deg c
At Outlet (O)
Mass flow 36.648 Kg/s
At Tip-Seal Inlet (TI)
Mass flow 03937 kg/sec
Total temperature 285.75 K
At Labyrinth Seal Outlet (LO)
Static Pressure 1428 KPa
Static temperature 284.39 K
Table 1
Figure 4 illustrates the simulation of the fluid flow inside the conventional flow guide element of figure 3. It is evident from the figure 4 that the flow suffers recirculation at the marked portion ‘M’ inside the flow guide element. Further  the flow takes a difficult deep turn at the marked portion ‘D’.

Several techniques have been disclosed in the prior art illustrating the optimization of flow guide elements in steam turbines.

US Patent Publication No: 2011158799 published on June 30  2011 titled “Radial channel diffuser for steam turbine exhaust hood” discloses an exhaust hood for an axial steam turbine that includes a radial channel  downstream from the normal flow pattern. The radial channel guides the exhaust steam flow in upper half of the hood in the flow momentum direction. Due to this pattern of flow direction  vortex generation in upper exhaust hood is reduced and increased flow diffusion results. The geometric arrangement can eliminate the outer casing of the exhaust hood over the axial length of the turbine inner casing  allowing the turbine inner casing to be supported directly by a foundation for the steam turbine.

US Patent No: 6261055 filed on August 3  1999 titled “Exhaust flow diffuser for a steam turbine” discloses an annular diffuser having its inlet located at the exit of a last row of blades of a steam turbine having initially very slowly increasing cross-sectional area with distance to accommodate the diffusion produced by the decaying wakes in the diffuser so as to prevent flow separation from diffuser walls and as a result to foster the diffusion process and to increase the efficiency of the steam turbine.

US Patent No: 5313700 filed on October 8  1992 titled “Forming a flow directing element for a turbine” discloses a flow directing element for the turbine section of a rotary machine includes various construction details which are developed which increase the aerodynamic efficiency of the flow directing element. In one embodiment  the flow directing element is a rotor blade having a roughened surface which approximates the critical roughness characteristic of the airfoil. In one particular embodiment  the roughness average of the surface lies between 120 to 200 AA micro inches.

None of the prior art mentioned above discloses a simple and cost effective flow guide element located between the modules of a turbine.
Therefore  there is a felt need for development of a diffuser located between the modules of a steam turbine which ensures in the smooth flow of the steam without formation of vortices and eddies.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide an optimized flow guide element located between the modules of the steam turbine which can prevent recirculation of steam and minimize flow separation losses.

Another object of the present invention is to provide a simple flow guide element to position between the modules of the steam turbine that can be easily manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates a divergent diffuser located at the exit of the last stage turbine blades;

Figure 2(a) illustrates a conventional flow guide element located between HP module and IP module of a steam turbine;

Figure 2(b) illustrates an enlarged view of the marked portion of figure 2(a);

Figure 3 illustrates a sector of analytical model of the conventional flow guide element of figure 2 to which boundary conditions are applied and simulation is run;

Figure 4 illustrates the simulation of the fluid flow inside the conventional flow guide element of figure 3;

Figure 5 illustrates a flow guide element in accordance with one embodiment of the present invention;

Figure 6 illustrates the simulation of fluid flow inside the flow guide element of figure 5;

Figure 7 illustrates a flow guide element in accordance with another embodiment of the present invention;

Figure 8 illustrates the simulation of fluid flow inside the flow guide element of figure 7;

Figure 9 illustrates the simulation of fluid flow inside the flow guide element with an increased chamfer at the marked portion ‘M’ of figure 8;

Figure 10(a) illustrates a cut sectional view of rotor to define geometry coordinates of the flow guide element of figure 8; and

Figure 10(b) illustrates an enlarged view of the flow guide element of figure 10(a) defining its geometrical coordinates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Figure 5 illustrates a flow guide element in accordance with one embodiment of the present invention.

Figure 6 illustrates the simulation of fluid flow inside the flow guide element of figure 5 run with the same boundary conditions tabulated in Table 1.

In accordance with one embodiment of the present invention  there is provided a flow guide element to which modifications has been done at the marked portions ‘M’ and ‘D’ of the flow guide element of figure 4. At the marked portion ‘M’  the sharp bend of the flow guide element is modified to a fillet of 13mm and at the marked portion ‘D’  the right angled deep turn of the flow guide element is inclined such that the flow follows a smooth stream line path without any recirculation as shown in figure 6.

Figure 7 illustrates a flow guide element in accordance with another embodiment of the present invention.

Figure 8 illustrates the simulation of fluid flow inside the flow guide element of figure 7 run with the same boundary conditions tabulated in Table 1.
In accordance with another embodiment of the present invention  there is provided a flow guide element to which a chamfered edge of 13mm is provided at the marked portions ‘M’ of the flow guide element 4 to facilitate in the ease of manufacturing (i.e.  Machining a fillet of 13 mm at the marked portions ‘M of the flow guide element is very difficult). It is evident from figure 8 that the flow is almost stream lined with a small acceptable zone of recirculation at the chamfered portion ‘M’.

Figure 9 illustrates the simulation of fluid flow inside the flow guide element with an increased chamfer at the marked portion ‘M’ of figure 8. Flow is analyzed by increasing the chamfer to 27mm at the marked portion ‘M’. It can inferred from the figure 9 that the recirculation zone at the chamfer portion ‘M’ has increased significantly to an unacceptable level.

Figure 10(a) illustrates a cut sectional view of rotor to define geometry coordinates of flow guide element of figure 8. The total length of the rotor is 4649 mm and is indicated by reference numeral X. The marked point (X1 and Y1) is taken as origin.

Figure 10(b) illustrates an enlarged view of the flow guide element of figure 10(a) defining its geometrical coordinates. The marked points (X2  Y2)  (X3  Y3)  (X4  Y4)  (X5  Y5)  (X6  Y6) and (X7  Y7) define the geometry of the flow guide element of figure 8.

It can be deduced that the chamfer of 13mm derived from various trial and error methods is acceptable only when the dimensions of the flow guide element are as per tabulated in Table 2.

Sl.No Geometry defining coordinates Value (mm)
1 (X1 Y1) (0  0)
2 (X2  Y2) (2222.47  300)
3 (X3  Y3) (2237.54  310)
4 (X4  Y4) (2268.05  372.59)
5 (X5  Y5) (2295.30  331 )
6 (X6  Y6) (2269.51  246)
7 (X7  Y7) (2269.54  235)
Table 2

Although the invention has been described herein above with reference to the embodiments of the invention  the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.

We claim:
1) A flow guide element for steam turbines located between the modules of the turbine  wherein a chamfer of 13mm is provided at the flow direction changing edge and flow obstructing vertical edge is inclined to facilitate the flow to follow a smooth streamline flow path.

2) A flow guide element for steam turbines located between the modules of the turbine as claimed in claim 1  wherein the profile defining coordinates of the
flow guide element are as follows:
Sl.No Geometry defining coordinates Value (mm)
1 (X1 Y1) (0  0)
2 (X2  Y2) (2222.47  300)
3 (X3  Y3) (2237.54  310)
4 (X4  Y4) (2268.05  372.59)
5 (X5  Y5) (2295.30  331 )
6 (X6  Y6) (2269.51  246)
7 (X7  Y7) (2269.54  235)

3) A flow guide element for steam turbines located between the modules of the turbine as claimed in claim1  wherein said chamfer of 13mm facilitates in the prevention of occurrence of recirculation zone.

4) A flow guide element for steam turbines located between the modules of the turbine  wherein a fillet of 13mm is provided at the flow direction changing edge and flow obstructing vertical edge is inclined to facilitate the flow to follow a smooth streamline flow path.

5) A flow guide element for steam turbines located between the modules of the turbine as claimed in claim 4  wherein said fillet of 13mm facilitates in the prevention of occurrence of recirculation zone.

6) A flow guide element for steam turbines located between the modules of the turbine as described herein the description and accompanying drawings.

Dated this 14th day of December  2011 (for Triveni Turbine Ltd)


Dr.Sunil Jajit
GM-IPR