IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613
Result Analysis and Discussion of Stress and Strain on Turbine Shaft Sujata Deshmukh1 Asst. Prof. A.P.Ninawe2 Dr.A.V.Vanalkar3 1 P.G. Student 2Assistant Professor 3Professor 1,2,3 Department of Mechanical Engineering 1,2,3 K.D.K College of Engineering Abstract— in this study the effect of mechanical forces on the steam turbine rotor shaft is carried out. The steam turbine is a mechanical device in which thermal energy of the pressurized steam is converted into rotation of the turbine shaft. This is achieved by reducing the pressure of steam as it passes over turbine blade. Due to the action of this steam mechanical forces acts on the turbine shaft. Stresses are induced due to these forces. For smooth working of turbine the stresses are need to study. The stresses are estimated by analytically calculating the mechanical forces and then these forces are applied on a CAD software model of the turbine shaft . Along with forces the material properties, boundary conditions are updated on the CAD model and analysis is done in ANSYS. Key words: CAD, FEM I. INTRODUCTION In the steam turbine the thermal energy in the pressurized steam is converted into the mechanical energy of rotation of shaft. This pressurized steam exerts tangential and axial thrust on the turbine shaft. Also a centrifugal thrust is acting on the turbine shaft due to the rotation of disc. The shaft under study consists of High pressure (HP), Intermediate pressure (IP) and Low pressure (LP) turbine shaft. There are total 25 Stages of HP shaft. The IP shaft is double flow axial turbine and it has total 20 +20 stages on either side. The LP turbine has total 6 + 6 stages. The size of blade for it is increasing towards the end. II. ANALYTICAL CALCULATION
Tangential load in N
Axial load in N
Centrifugal load in N
Stage 1
33700
1431
8575920
2
34400
662
8695350
3
34000
661
8633772
4
35000
720
8662857
5
36660
660
8679466
6
37000
295
8882508
Lp turbine
Mechanical load on turbine shaft A. FEM Analysis: The FEM analysis is carried out by using ANSYS software. As the geometry under study is axis symmetric only one degree model is considered for the study. The model for HP, IP and LP shaft is converted into IGES format. The model of each shaft without blades is considered. The models are meshed using solid 187 element in ANSYS. Solid 187 is a higher order tetrahedral 3-D element having 10 nodes. It is most suitable for meshing irregular geometry. Then suitable boundary conditions are applied which simulate the actual working environment of turbine shaft. The analytically calculated forces are then applied on the slice of shaft. The forces are applied on the upper surface (grooves) of the shaft. III. RESULT AND DISCUSSION A static structural analysis is carried out and following results are obtained. For HP shaft
The tangential and axial forces are calculated by drawing velocity diagram per stage. The centrifugal force is calculated by using conventional formula. Mechanical load on turbine shaft The following table shows the tangential, axial and centrifugal forces per stage. Tangential load
Axial load
Centrifugal load
Hp turbine
Newton
N
N
(stage 1-25)
17380
880
926258
Stage 1
20680
440
1359823
2
20680
440
1695877
3
20300
220
1491986
4
20300
220
1524344
5
21120
440
1854589
6
21120
440
1917145
7
21560
660
1972720
8
21560
660
2042091
9
22000
550
2112644
10
22000
550
2184356
11
22550
880
2257297
12
22550
880
2331397
13
23100
660
2406679
14
23100
660
2497334
15
23540
1100
2575179
16
23540
1100
2639622
17
24200
660
2704854
18
24200
660
2770874
19
24640
440
2868032
20
24640
440
2951395
IP turbine
The equivalent stress (von –mises) is shown in the above fig. The maximum equivalent stress is 442.31Mpa. The distribution of stress is shown in the above fig. The value of stress is more at the upper portion of the shaft and it is reducing towards the central axis of shaft.
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