Structural Analysis and Balancing Test for Impeller Before Conducting Over Speed Test

Transcription

1 International Journal of Electrical Electronics Computers & Mechanical Engineering (IJEECM) ISSN: Volume 3 Issue8 ǁ Aug IJEECM journal of Mechanical Engineering (ijeecm-jme) Structural Analysis and Balancing Test for Impeller Before Conducting Over Speed Test S.Rakesh 1, J.Govardhan 2 1,2 Electrical & Electronics Department, 1,2 AVN Institute of Engineering and Technology, Koheda Road, Ibrahimpatnam, Ranga Reddy Dist., T.S(India) Abstract This project is process structural analysis and balancing test for impeller before conducting over speed test of manufacturing a component, it is essential to check various properties of the component that may get changed after the manufacturing process. The Centrifugal Compressor Impellers are manufactured from forgings, which is the basic raw material for impellers. During the process of producing the impeller from the forgings, the forgings have to undergo many machining operations and welding processes. These operations may change the mechanical properties and these changes should be accounted in order to have good performance and accuracy. Since the impeller is a high speed rotating component, some stresses may get induced in it and cause dimensional inaccuracies depending upon the mechanical properties of the component material. Hence each Impeller of the Compressor rotor is individually over speed in a vacuum chamber to a value of 115% of Maximum continuous speed to check the mechanical soundness of the impeller. After that dimensional and Dye checks are carried out on oversped impellers for any permanent deformations and micro cracks at the welds. The whole process should be done before the impeller is made ready to be mounted on the rotor shaft. Before conducting the Over Speed Test (O.S.T.) on the impeller, first it has to be balanced. The reasons for balancing, procedure to be followed and the detailed description of the over speeding test are discussed below. Keywords: solidworks, ansys. I. INTRODUCTION In the process of manufacturing a component, it is essential to check various properties of the component that may get changed after the manufacturing process. The Centrifugal Compressor Impellers are manufactured from forgings, which is the basic raw material for impellers. During the process of producing the impeller from the forgings, the forgings have to undergo many machining operations and welding processes. These operations may change the mechanical properties and these changes should be accounted in order to have good performance and accuracy. Since the impeller is a high speed rotating component, some stresses may get induced in it and cause dimensional inaccuracies depending upon the mechanical properties of the component material. Hence each Impeller of the Compressor rotor is individually oversped in a vacuum chamber to a value of 115% of Maximum continuous speed to check the mechanical soundness of the impeller. After that dimensional and Dye checks are carried out on over-sped impellers for any permanent deformations and micro cracks at the welds. The whole process should be done before the impeller is made ready to be mounted on the rotor shaft. Before conducting the Over Speed Test (O.S.T.) on the impeller, first it has to be balanced. The reasons for

2 balancing, procedure to be followed and the detailed description of the over speeding test are discussed below. 2. DIESEL ENGINE A diesel engine is an internal combustion engine. The cycle of the cylinders is the same in a diesel engine as it is in a gasoline engine, assuming it is a four-stroke engine Aside from the fuel type, the major difference between the two engines is the combustion itself. A gasoline engine uses a spark plug to initiate combustion. A diesel engine compresses the air then injects the fuel into the cylinder at the top of the stroke. The high temperature of the compressed air ignites the fuel. The hot gases expand, force the piston down, and create a torque on the crankshaft. The final stroke is the exhaust stroke, which releases the hot gases into the exhaust system. Turbo machines are devices in which energy is transferred either to or from, a continuously flowing fluid by the dynamic action of moving blades of the runner. Leonardo Da Vinci ( ) was probably the first to coin the idea of lifting water by centrifugal forces. He has described primitive models of turbomachines by making some sketches. From his original sketches, a French physicist Denis Papin was first to describe the centrifugal pump scientifically in He built first pump in 1705, which had impeller with blades and a volute. Thus, centrifugal pumps and blowers of today are made after more than 300 years of revolution. 4. DESIGN OF IMPPLER Figure 1 Diesel Engine Four-Stroke Cycle DIESEL ENGINE FOUR-STROKE CYCLE The torque created from the downward motion of the piston acting on the crankshaft is transmitted from the crankshaft to the flywheel and into the transmission. To increase power to the transmission, the power must be increased in the cylinder. There are several ways to increase the power of an engine. One of the more common ways of increasing engine power is to increase the airflow into the cylinder by increasing the density of the air entering the cylinder.1 A turbocharger uses waste energy from the exhaust system to compress air entering the cylinder, thus increasing engine power. Figure 2 Impeller 3. LITERATUTE REVIEW

3 dimensions called Finite Elements. The original body or the structure is then considered as an assemblage of these elements connected at a finite number of joints called Nodes or Nodal Points. Simple functions are chosen to approximate the displacements over each finite element. Such assumed functions are called shape functions. This will represent the displacement with in the element in terms of the displacement at the nodes of the element. 5. ANALYSIS RESULTS Imported model in to ansys AISI 4063 Steel Figure 2 Impeller CATIA Model Figure 3 Impeller 3-D Model Figure 6 Imported models in to ansys Element Type: solid 20 nodes 95 Material Properties: MESHED MODEL Youngs Modulus (EX) : 209 GPA Poisson s Ratio (PRXY) : 0.29 Density : 7.75 g/cc Tensile strength ultimate: 1855 MPA Tensile strength yield : 1593 MPA Figure 4 Impeller Blades Shapes 4. ANALYSIS INTRODUCTION TO FEA The Basic concept in FEA is that the body or structure may be divided into smaller elements of finite

4 Rotating speed: RPM Displacement Figure 7 Meshed Model Figure 50 Stain INCONEL 718 Element Type: Solid 20 node 95 Material Properties: Youngs Modulus (EX) : 205 GPA Poissons Ratio (PRXY) : Density : 8.19 g/cc Tensile strength ultimate: 1120 MPA Tensile strength yield : 827 MPA Rotating speed :13000 RPM Displacement Figure 8 Displacement Figure 11 Displacement STRAIN Figure 9 Stress

5 STRAIN Figure 12 Stress Figure 14 Displacement Figure 13 Stain Titanium Ti Element Type: Solid 20 node 95 Material Properties: Youngs Modulus (EX) : 114 GPA Displacement Poissons Ratio (PRXY) : 0.33 Density : 4.65 g/cc Tensile strength ultimate: 1580 MPA Tensile strength yield : 1410 MPA Rotating speed :13000 RPM STRAIN Figure 15 Stress Figure 16 Strain

6 Technetium Element Type: Solid 20 node 95 Material Properties: Youngs Modulus (EX) : 322 GPA Poissons Ratio (PRXY) : 0.31 Density : 11.5 g/cc Tensile strength ultimate: 1510 MPA Tensile strength yield : 1290 MPA Rotating speed :13000 RPM Displacement Figure 19 Stain 6. RESULTS OF FINITE ELEMENT ANALYSIS Table 1 Result Tables Figure 17 Displacement Name of the Material DISP mm N/mm 2 STRAIN AISI 4063 Steel INCONEL E E -06 Titanium Ti E -06 Technetium E- 06 STRAIN Figure 18 Stress FEA has become a solution to the task of predicting failure due to unknown stresses by showing problem areas in a material and allowing designers to see all of the theoretical stresses within. This method of product design and testing is far superior to the manufacturing costs which would accrue if each sample was actually built and tested. In practice, a finite element analysis usually consists of three principal steps: 1. Preprocessing: The user constructs a model of the part to be analyzed in which the geometry is divided into a number of discrete sub regions, or elements," connected at discrete points called nodes." Certain of these nodes

7 will have fixed displacements, and others will have prescribed loads. These models can be extremely time consuming to prepare, and commercial codes vie with one another to have the most user-friendly graphical preprocessor" to assist in this rather tedious chore. Some of these preprocessors can overlay a mesh on a preexisting CAD file, so that finite element analysis can be done conveniently as part of the computerized drafting-and-design process. 2. Analysis: The dataset prepared by the preprocessor is used as input to the finite element code itself, which constructs and solves a system of linear or nonlinear algebraic equations Kijuj = fi where u and f are the displacements and externally applied forces at the nodal points. The formation of the K matrix is dependent on the type of problem being attacked, and this module will outline the approach for truss and linear elastic stress analyses. Commercial codes may have very large element libraries, with elements appropriate to a wide range of problem types. One of FEA's principal advantages is that many problem types can be addressed with the same code, merely by specifying the appropriate element types from the library. 3. Post processing: In the earlier days of finite element analysis, the user would pore through reams of numbers generated by the code, listing displacements and stresses at discrete positions within the model. It is easy to miss important trends and hot spots this way, and modern codes use graphical displays to assist in visualizing the results. A typical post processor display overlays colored contours representing stress levels on the model, showing a full field picture similar to that of photo elastic or moiré experimental results. 7. CONCLUSION Hence we can conclude that Over-speed testing of large industrial and utility compressor rotors offers many benefits to the end user because the objectives of over-speed testing include Helping the end user feel more comfortable knowing that these huge rotors have been tested at speeds well in excess of the actual maximum operating speed. A second benefit is that inspection of the rotor welded joints before and after testing (using nondestructive inspection techniques) provides further proof that the rotor can tolerate such high stress levels without cracks developing. A third benefit is that subjecting the rotor to even one cycle at such high stress levels offers an advantage regarding the rotor's fatigue life. These factors provide comprehensive proof that the materials and workmanship. incorporated into the rotor have resulted in equipment that is safe to operate even at speeds above the expected operating range. Hence Over-speed testing does more than just provide a warm and fuzzy feeling. 8. REFERENCES 1. J. Wang, Piechnajanusz, et al. A novel design of composite water turbine using CFD. Journal of Hydrodynamics, 2012, 24(1): R. Barrio, J. Parrondo, E. Blanco. Numerical analysis of the unsteady flow in the near-tongue region in a volute-type centrifugal pump for different operating points. Computers & Fluids, 2012, 39: J. Wang, B. gower, N. M uller. Numerical investigation on composite material marine current turbine using cfd. Central European Journal of Engineering, 2011, 1(4): J. Wang, J. Piechna, N. M uller. Numerical investigation of the power generation of a ducted composite material marine current turbine. Journal of Zhejiang University-SCIENCE A, 2013, 14(1): S. Anagnostopoulos. A fast numerical method for flow analysis and blade design in centrifugal pump impellers. Computers & Fluids, 2009, 38: C. Lam, K. Bremhorst. Modified form of model for predicting wall turbulence. ASME Journal of Fluids Engineering, 1981, 103:

8 7. M. Nataraj, R. Ragothsingh. Analyzing pump impeller for performance evaluation using rsm and cfd. Desalination and Water Treatment, ahead of print, 2013, Technical paper. Advanced boundary cartesian meshing technology in solidworks flow simulation. in: Dassault- Systemes, SolidWorks corporation, Engineering, Delhi University and bachelors from Institute of Engineers (India). He served defence for 20 years. Also has 16 years of teaching experience in various positions at Padmasri BV Raju Institute of Engineering and Technology, Narsapur, DVR College of Engineering and Technology, Kandi and PRRM College of Engineering and Technology, Shabad. He is presently Principal of AVN Institute of Engineering and Technology at Hyderabad. 9. Technical paper. Enhanced turbulence modeling in solidworks flow simulation. DassaultSystemes, SolidWorks corporation, R. Ragothsingh, M. Nataraj. Parametric study and optimization of pump impeller by varying the design parameter using computational fluid dynamics. International Review of Mechanical Engineering, 2012, 6: M. Shojaeefard, M. Tahani, et al. Numerical study of the effects of some geometric characteristics of a centrifugal pump impeller that pumps a viscous fluid. Computers & Fluids, 2012, 60: R. Singh, R. Nataraj, et al. Investigation of a centrifugal pump impeller vane profile using cfd,. International Review on Modelling and Simulations, 2013, 6(4): [K. Srinivasan. Rotodynamic pumps (centrifugal and axial). New age international, Mr.S.Rakesh M.tech student, AVN Institute of Engineering and Technology, under Jawaharlal Nehru Technological University Hyderabad (JNTUH). Bachelor of engineering from AVN Institute of Engineering and Technology,I am Participated in many technical events and activities.my main project is completed on anti lock braking system(proto type)from santha shivam industry Pvt.Ltd,Coimbatore,tamilnadu. 14. W. Zhou, Z. Zhao, et al. Investigation of flow through centrifugal pump impellers using computational fluid dynamics. Journal of Rotating Machinery, 2003, 9(1): Dr. J. Govardhan holds Ph.D in Mechanical Engineering from Osmania University, Hyderabad. He obtained his Masters degree from Delhi College of