design and analysis of turbine blade of · pdf file · 2015-04-10for reducing...

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Int. J. Mech. Eng. & Rob. Res. 2014 Sujeet S Narkhede and A Pateriya, 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 3, July, 2014

© 2014 IJMERR. All Rights Reserved

Review Article

DESIGN AND ANALYSIS OF TURBINEBLADE OF ENGINE - A REVIEW

Sujeet S Narkhede1* and A Pateriya1

*Corresponding Author: Sujeet S Narkhede � [email protected]

This paper involves various failure mechanisms and the general practices followed by a bladedesigner for deciding a blade configuration were also described. Although some significantadvances have been made during past some decades in the design technology of the bladefrom vibration point of view. First the designing of the blade geometry completed with CADsoftware and analysis with the analysis software. Blade failures still continue to take place, andhence efforts are still on to understand in totality the blade dynamics which has caused in largenumber of technical papers. Some of important are presented here. In this review stress isplaced on paper dealing with general structural analysis of blade by analytical modeling, bladeexcitation and fatigue life estimation of turbine blade.

Keywords: Review, Design, Turbine blade, Failures

INTRODUCTION

The turbine is a rotary mechanical device thatextracts energy from a fluid flow and convertsinto useful work and purpose of turbinetechnology are to extract the maximumquantity of energy from the working fluid toconvert it into useful work with maximumreliability, minimum cost, minimumsupervision and minimum starting time.

CFX-Blade Genis an advanced, interactiveblade design tool for turbo machinerymodeling developed by AEA TechnologyEngineering Software Inc. Blade Gen

1 Department of Mechanical Engineering, Pdm.Dr.V.B. Kolte College of Engineering, Malkapur, Maharashtra, India.

incorporates year softurbo-machinerydesignand analysis expertise into aneasy touse graphical environment utilizing termino-logy familiar to engineers involved in thedesign of rotating machinery. With Blade Gen,the user can re-design existing blades toachieve new design objectives or createcompletely new blade designs from scratch.

Blade Gen represents a pivot all inkbetween blade design, advanced fluidanalysis and manufacturing. Used incombination with the CFX-Blade Gen plusAnalysis Module, users can rapidly evaluatethe performance ofa component. Alternately,

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the geometry can be exported through CFX-Turbo Gridto CFX-TASC flow to provideamorerigorous analysis.

It also produces blade geometry files thatcan be exported to CAD design in packagesuch as CATIA and AutoCAD. This enablesthe user to efficiently transition frompreliminary blade design, to full3D viscousflow analysis, and finally to a CADenvironment.

BENFITS USING BLADEGEN

• Users should first describe themeridional profile earlier defining theAngle / Thickness or Pressure / Suctionviews, since these views staydependent on the path length of themeridional profile’s layers.

• The Angle, Thickness, and Pressure/Suction Views define parameters on alayer. The first layer must be the huband the second must be the shroud,with additional layers inserted at a user-specified fraction of the span. If only onelayer is defined, it applies to the entirespan between hub and shroud.

• All views display the same layer andblade. If a view doesn’t have a definitionfor a particular layer that is beingdisplayed, the calculated values at thatlayer are displayed.

FAILURES

Losses on the turbine consist of themechanical loss; tip clearance loss,secondary flow loss and blade profile lossetc. More than 60% of total losses on theturbine is generated by the two latter loss

mechanisms. These losses are directlyrelated with the reduction of turbine efficiency.In order to provide a new design methodologyfor reducing losses and increasing turbineefficiency, a three-dimensional axial-typeturbine blade shape will be designed by usingCAD software like ProE or CATIA andoptimization of design will be perform byanalyzing different parameters using ANSYSworkbench software.

Turbine efficiency is the most importantfactor on the performance of heavy duty gasturbines for power plants, air turbines, or turboexpanders etc. This efficiency is related veryclosely with losses in the passage. Losseson the turbine consist of mechanical lossesdue to the friction of rotating parts or bearings,tip clearance losses due to the flow leakagethrough tip gap, secondary flow losses dueto curved passages, and profile losses dueto the blade shape. So, it needs to develop anew design technology for providing anoptimum turbine blade profile with eithersame or different material.

Figure 1: Blade Geometry of Turbine(Source Patent No. US6984112B2)

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The break down and failures of turbomachineries have been influencing such asconsequential damages andmost importantlythe cost to repairs. To avoid these, it isobvious that the blading of turbo machinerymust be made structurally stronger, thatmeans not in dimensions and/or use ofmaterials of construction, but keeping theoperating stresses well within the limits.

Turbo machinery blades are classified intotwo categories depending on their mannerof operation as either impulse or reactionblades. Impulse blades function byredirecting the passing fluid (steam or gas)flow, through a specified angle.

Reaction blades function as airfoils bydeveloping a gas dynamic lift from thepressure difference, which the airfoil causes,between the blades upper and lowersurfaces. High-pressure stages are generallyimpulse stages and low- pressure stages arereaction stages. Thus, a single free standingblade can be considered as pre-twistedcontinuous beam with an asymmetric airfoilcross-section mounted at a stagger angle ona rotating disc.Reasons for failure of bladeddisc are Excessive stresses, Resonance dueto vibration, operating environmental effects.

High cycle fatigue plays a significant rolein many turbine blade failures. Duringoperation, periodic fluctuations in the steamforce occur at frequencies, corresponding tothe operating speed and harmonics andcause the bladed disk to vibrate. Theamplitude of these vibrations depends in partof the natural frequencies of the bladed diskto the forcing frequency. Large amplitudevibration can occur when the forcingfrequency approaches or becomes resonant

with the natural frequency of the blades.Steam turbine manufacturers typically designand manufacture blades with adequatemargins between the forcing frequencies andthe fundamental natural frequencies to avoidresonance.

FAILURESIN STEAM

TURBINE BLADES

In the following paragraphs various failuremodes of the turbine blade are discussedalong with different kinds of stresses in theblade and the nature of aerodynamicexcitation. A brief discussion of each of theabove failure mechanisms follows in orderto understand their significance.

Excessive Stress

The total stress at any location of the bladeis sum of the centrifugal tension, centrifugalbending, steady steam bending and thealternating bending. The amplitude ofalternating bending depends on the dynamicbending force, damping factor and theresonant frequency. Each of these is brieflydiscussed below to high light theirimportance.

Centrifugal Stress

In steam turbine, centrifugal stress is neverthe main cause of a blade failure, except inthe rare cases of turbine run-away or due tolow cycle fatigue caused by frequent startups/shutdowns. However, centrifugal stressis an important contributing factor with fatiguefailure, corrosion fatigue failure and stresscorrosion failures. The level of centrifugalstress is kept at such a level so as to haveenough margins for alternating stress. Theblade configuration is designed so as to keepthe center of gravity of shroud, airfoil and root

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attachments, on common radial axis. Thisprevents centrifugal induced torsion stresses.

ANALYTICAL MODELING

There has been a continuing improvementin the analytical modeling for thedetermination of natural frequencies of thesystem comprising of a set of blades mountedon the bladed disk. The early attempts tomodel the blade as a beam element havegradually led to a more detailed finite elementrepresentation. This finite elementrepresentation of real blade profile becomesnecessary especially when plate or shell typeof vibratory modes is induced.

Le-Chung Shaiu and Teng-Yuan Wa(1997), studied the free vibration behavior ofbuckled composite plates by using finiteelement method. Unlike beams or columns,plates can carry a much-increased load afterbuckling without failure. Here triangular plateelement is taken for finite element analysis.This element is developed based on asimplified high order plate theory and largedeformation assumptions. The nonlineargoverning equationsofmotion forplates islinear zed into two sets of equations byassuming small amplitude vibration of thelaminates about its buckled static equilibriumprofile. In the post buckling region, thebuckled plate may shift from are bucklingmode to another. Due to this buckle patternchange, plate is also suddenly changedwhich in turn makes the natural frequenciesof the plate to have sudden jump. Thebuckling mode of plates shifted from first tosecond. Then the stiffness of the plate isincreased which makes a sudden increasein natural frequencies.

Hu X X and Tsuigi T (1999), had done freevibration analysis on curved and twistedcylindrical thin panels. Blades are part ofturbomachinery rotating at high speed, so itis important to ensure safety while rotating.A turbomachinery blade is treated as acylindrical thin panel twist, chordwise andspanwise curvatures along lengthwisedirection. The non-linear strain-displacementrelations of the model are derived based onthe general thin shell theory and anumericalmethod for analyzing the freevibrations of curved and twisted cylindricalthin panels is presented by means of theprinciple of virtual work for the free vibrationusing Raleigh-Ritz method. It is shown thatthe method is effective for analyzing the freevibrations of the turbomachinery blades, andcan provide accurate results when the propernumber of integrating points and terms ofdisplacement functions are adopted. Theeffects of curvature and twist on the vibrationsare studied. This method is adequate forevaluating the vibration characteristics evenif the models have large curvatures and largetwists.

Rao J S (1974), made a two-dimensionalanalysis of free vibrations in the tangentialdirection. The first step is to develop thepotential and kinetic energies for thetangential motion of the blades and shrouds.Second, Hamilton’s principle is applied toderive the differential equation of motion andthe boundary conditions.

Tsuiji and Sueoka (1990), deal with the freevibration of cylindrical panels by usingRaleigh-Ritz method. Blades of turbomachinery are twisted in axial direction andcambered in the chord wise direction. The

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blade has been idealized to a twistedcantilevered cylindrical panel and numericalmethods have investigated its vibratorycharacteristics. The convergence offrequency parameters is studied with theincrease of number of strip and of terms inassumed solution functions. To demonstratethe usefulness of the method, the frequencyparameters obtained. The frequencyparameters and the modes of vibration areanalyzed for typical twisted cylindrical panelsand the effect of pre twist on them isinvestigated.

Leissa, MacBain and Kielb (1984), madea comprehensive study of the numerousprevious investigations on the free vibrationof twisted cantilever plates of rectangularplatform which are results of a joint industry,government and university effort.Theoreticalresults received from different FEM programsutilizing shell theory and beam theory werecompared with two independent sets of dataobtained from experiments.Reasonableagreement among the theoretical results wasfound but it was recommended that furtherimprovement in analysis method is necessaryfor increased dependability.

Sagar P Kauthalkar and Devendra SShikarwar, had investigated the deformationsand stresses induced in blade geometry theyhave found out the maximum elongations andtemperatures are observed at the blade tipsection and minimum elongation andtemperature variations at the root of theblade. Temperature distribution is almostuniform at the maximum curvature regionalong blade profile. Temperature is linearlydecreasing from the tip of the blade to theroot of the blade section. Maximum stress

induced is within safe limit. (Michel Arnal,2007).

Avinash V Sarlashkar, Girish A Modgil,Mark L Redding summarizes the architectureand capabilities of Blade Pro, an ANSYSbased turbine blade analysis system withextensive automation for solid model and F.E.model generation, boundary conditionapplication, file handling and job submissiontasks for a variety of complex analyses.

CONCLUSION

In this paper, analyzed previous generals anddesigns of the gas turbine blade to do furtheroptimization, Finite element results for freestanding blades give a complete image ofstructural characteristics, which can utilizedfor the improvement in the design and theoperating conditions. From the review it canbe noted that there are various factors likeblade angle, blade geometry, number ofperforated holes and the material of the bladecan affect structural as well as thermalstresses.

REFERENCES

1. A H Shah, G S Ramsekhar and Y M Desai(2002), “Natural Vibration of LaminatedComposites Beams by Using Fixed FiniteElement Modeling”, Journal of the soundand vibration, Vol. 257, pp. 635-651.

2. Avinash V Sarlashkar (2001), “BladeProTM: An ANSYS-Based Turbine BladeAnalysis System”, Impact Technologies,LLC, Rochester, NY 14623, U.S.A Yoo HH, J Y Kwak and J Chung, Vibrationalanalysis of rotating pre twisted bladeswith a concentrated mass, Journal ofsound and vibration, Vol 240, No. 5, pp.

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891-908.

3. Hu, XX and T Tsuiji (1999), FreeVibrational Analysis of Curved andTwisted Cylindrical thin Panels”, Journalof Sound and Vibration, Vol. 219, No. 1,pp. 63-68.

4. J S Rao, R Bahree and A M Sharan(1989), “The Design of Rotor BladesTaking into Account the Combined Effectsof Vibratory and Thermal Loads”,Transactions of ASME, Journal ofEngineering gas turbines and Power, Vol.111, pp. 610-618.

5. Le-chungshiau and Teng-yuanWu (1997),“Free Vibration of Buckled LaminatedPlates by Finite Element Method”,Transactions of the ASME, Journal ofVibrations and Acoustics, Vol. 111, pp.635-644.

6. Leissa A W, Macbin J C and Keilb R E

(1984), Vibration of Twisted CantileverPlates Summary of Provisions; CurrentStudies”, Journal of sound and vibration,Vol. 96, Vol. 20, pp. 159-167.

7. Michel Arnal (2007), “Fluid StructureInteraction Makesfor Cool Gas TurbineBlades”, ANSYS Advantage, Vol. 1, No.1.

8. Rao J S (1974), “Application of VariationalPrinciple to Shrouded Turbine B2lades”,Proceedings of 19th cong. ISTAM, pp. 93-97.

9. Sagar P Kauthalkar (2008), “Analysis ofThermal Stresses Distribution Pattern onGas Turbine”, International Journal ofEngineering, Education and Technology(ARDIJEET) ISSN 2320-8.

10. Tsuneo Tsuji and Teisukesueoka (1990),“Vibrational Analysis of Twisted thinCylindrical Panels by Using Raleigh-Ritzmethod”, JSME International Journal,Series iii, Volume 33, pp. 501-505.

design and analysis of turbine blade of · pdf file · 2015-04-10for reducing...

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