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Int. J. Mech. Eng. & Rob. Res. 2014 Kevin A Patel and Devendra A Patel, 2014

FE ANALYSIS OF RUNNER BLADE FOR WELLSTURBINE

Kevin A Patel1* and Devendra A Patel1

*Corresponding Author: Kevin A Patel,Kevinpatel41@gmail.com

One of the major sources of stress arising in turbo machinery blades are centrifugal loadsacting at any section of aerofoil. According to this phenomenon stress evaluation of bladeattachment region in the disc has to be performed in order to avoid the blade failure. This papersummarizes FE analysis of wells turbine blade, on which Pro- E is used for deign of solid modelof the turbine blade with the help of the spline and extrude options ANSYS 11.0 Software is usedanalysis of FE model generated by meshing of the blade using the solid brick element present inthe ANSYS software itself and thereby applying the boundary condition. Then ANSYS preprocessor to analyse the complex geometries and performance of the blade for differentmaterials. Finally stating the best suited material among the three from report generated afteranalysis. Result can be compared with mechanical properties of turbine blade materials.

Keywords: Wells turbine rotor, FEA, Aerofoil, Stress, Different material

INTRODUCTIONScientists have been investigating anddefining different methods for power extractionfrom the wave motion. These devices utilizethe principle of Oscillating Water Column(OWC). OWC based wave energy power plantconvert into low pressure pneumatic power inform of bi-direction of air flow. Then wellsturbine currently uses around world for waveenergy power generation. Wells turbineintroduced Dr. A. A. Wells in 1976. The Wellsturbine was proposed as a form of self-

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Int. J. Mech. Eng. & Rob. Res. 2014

1 Department of Mechanical Engineering, Chhotubhai Gopalbhai Patel Institute of Technology, Bardoli.

rectifying axial flow air turbine which is suitablefor wave energy conversion in OWC. There aremany reports which investigate theperformance of the Wells turbine both on thestarting and running characteristics. Accordingto these results, however, the Wells turbine hasinherent Disadvantages: lower efficiency,poorer starting, higher noise level and higheraxial thrust in comparison with conventionalturbines.

In order to overcome these drawbacks andto determine the optimum turbine geometry,

Research Paper

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Int. J. Mech. Eng. & Rob. Res. 2014 Kevin A Patel and Devendra A Patel, 2014

various researches have conducted studiesand published papers in relation to the rotorblade profile for the Wells turbine. Accordingto previous studies, symmetrical airfoil ofNACA four digit series is preferable one,especially it has been shown that the NACAfour digit series with thickness ratio ofapproximately 20% is recommended one forthe rotor blade.

Importance of FEMThe Finite Element Method (FEM), sometimesreferred to as Finite Element Analysis (FEA),is a computational technique used to obtainapproximate solutions of boundary valueproblems in engineering. Simply stated, aboundary value problem is a mathematicalproblem in which one or more dependentvariables must satisfy a differential equationeverywhere within a known domain ofindependent variables and satisfy specificconditions on the boundary of the domain.Boundary value problems are also sometimescalled field problems. The field is the domainof interest and most often represents aphysical structure. The field variables are thedependent variables of interest governed bythe differential equation. The boundaryconditions are the specified values of the fieldvariables (or related variables such asderivatives) on the boundaries of the field.Depending on the type of physical problembeing analyzed, the field variables may includephysical displacement, temperature, heat flux,and fluid velocity to name only a few.

A General Procedure for FiniteElement AnalysisCertain steps in formulating a finite elementanalysis of a physical problem are common to

all such analysis, structural, heat transfer, fluidflow, or some other problem. These steps areembodied in commercial finite elementsoftware packages and are implicitlyincorporated. The steps are described asfollows.

Pre-ProcessingThe pre-processing step is, quite generally,described as defining the model and includes:

Step 1: Define the geometric domain of theproblem.

Step 2: Define the element type(s) to be used.

Step 3: Define the material properties of theelements.

Step 4: Define the geometric properties of theelements (length, area, and the like).

Step 5: Define the element connectivity’s(mesh the model).

Step 6: Define the physical constraints(boundary conditions).

Step 7: Define the loadings.

SolutionDuring the solution phase, finite elementsoftware assembles the governing algebraicequations in matrix form and computes theunknown values of the primary field variable(s).The computed values are then used by backsubstitution to compute additional, derivedvariables, such as reaction forces, elementstresses, and heat flow. As it is not uncommonfor a finite element model to be represented bytens of thousands of equations, special solutiontechniques are used to reduce data storagerequirements and computation time. For static,linear problems, a wave front solver, based onGauss elimination, is commonly used.

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Post ProcessingAnalysis and evaluation of the solution resultsis referred to as post processing.Postprocessor software containssophisticated routines used for sorting,printing, and plotting selected results from afinite element solution. Examples of operationsthat can be accomplished include:

1. Sort element stresses in order of magnitude.

2. Check equilibrium.

3. Calculate factors of safety.

4. Plot deformed structural shape.

5. Animate dynamic model behaviour.

6. Produce color-coded temperature plots.

Importance of Finite ElementAnalysis in Turbo MachineryTurbo machinery blades are usually exposedto very hostile operating conditions and failureof a single blade may lead to major secondarydamage of the machine. This explains why thevibration characteristics of turbo machineblades have been studied in such great detail.Most investigations have dealt with axial-flowturbo machines rather than radial-flow ones.This is mainly due to the fact that the formercategory has been, possibly used extensivelyin aircraft propulsion, which is perceived to bea more critical application. However, greaterknowledge of the vibration behaviour of radial-flow impellers will be useful for optimizing theirfatigue-life and efficiency resulting inincreased performance and applicability.

PROBLEM DEFINITION ANDPRESENT WORKThe present work includes the simulation(structural analysis) of axial turbine subjected

to centrifugal stresses due to rotational speed.Due to complicated shape of the blade it isnot possible to calculate the stresses of rotorblade using analytical method. Hence Pro-E5.0, a solid modeling and a finite elementpackage are used to calculate the stressesfor complex geometry of rotor blades. Stressanalysis can be viewed by postprocessorphase of ANSYS’11.

It is applied to the design of wells turbinerotor with blade. A streamline curvature methodis used for the solution of the meridional flowand a singularity method is utilized for theblade-to-blade flow.

The Four type rotor blades are radially setbetween two coaxial cylindrical wall surfaces.The outer-diameter is D0 = 0.298 m and theinner diameter is Dh = 0.208 m.

MODELLING AND MESHINGThe modelling of wells turbine has been donein Sheet metal module of commercial softwarePro-E 5.0 then the geometry made in thePro-E 5.0 parametric is converted in to the stepfile (.stp format) and then it is import in theANSYS for the meshing and the boundaryconditions.

The geometry is drafted based on thedimensions of geometric design parameters.The rotor with one blade geometry is 3-dimensionally modelled then meshed properlyto divide it into elements and nodes. Finiteelement model was generated using freemeshed 4 nodes quadratic tetrahedral elementdue to their flexibility in curved and complexshapes, which has three degrees of freedomper node, i.e., translation in x, y, z directionswere used. Quality checks and meshoptimization for elements were also performed

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Int. J. Mech. Eng. & Rob. Res. 2014 Kevin A Patel and Devendra A Patel, 2014

taking into consideration of aspect ratio,distortion, stretch. For analysis work,geometric and FE models with meshing forrotor with blade is presented as followingimages:

The Structural boundary conditions for thesimulation are shown in Figure 4 at rotationalSpeed ranging from 1000 rpm to 5000 rpmwhereas the material properties was changesby keeping all dimensions same as providesin data. Also applied to fixed support.

ANALYSIS RESULTThe results obtained are presented in the formof counter maps and profiles of radialelongation, mechanical stresses on bladesurface for the rotor blade of axial flow wellsturbine.

Above figure displays the stressesdeveloped for the Aluminium rotor consideringa speed of 5000 rpm. Similar steps were

Figure 1: Geometry Model of One BladeRotor

Figure 2: FE Model with Meshing

Figure 3: Wells Turbine Rotor Bladewith Boundary Conditions on It

Figure 4: Equivalent Stress AnalysisResults on Wells Turbine Rotor Blade

at 5000 rpm

Figure 5: Centrifugal Stress TotalDeformation Analysis Results on Wells

Turbine Rotor Blade

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Int. J. Mech. Eng. & Rob. Res. 2014 Kevin A Patel and Devendra A Patel, 2014

1000 0.915 2.682 2.627 0.0011 0.0011 0.0011

2000 3.662 10.728 10.509 0.0043 0.0043 0.0043

3000 8.239 24.137 23.646 0.0096 0.0096 0.0096

4000 14.646 42.911 42.038 0.017 0.0171 0.00171

5000 22.885 67.048 65.684 0.0266 0.268 0.0268

Table 1: Maximum Stresses and Total Deformation at Various Speeds for DifferentMaterial

Speed (rpm)Equivalent Stress (Mpa) Total Deformation (mm)

Aluminum Inconel S.S.310A Aluminum Inconel S.S.310A

Figure 6: Maximum Stresses for Rotor at Various Speeds for Different Material

Speed (RPM)

Figure 7: Maximum Displacements for Rotor at Various Speeds for Different Material

Speed (RPM)

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Int. J. Mech. Eng. & Rob. Res. 2014 Kevin A Patel and Devendra A Patel, 2014

performed by taking different material andcalculating the stresses at different speedranging from 1000 rpm to 5000 rpm with anincrement at speed of 1000 rpm.

DISCUSSIONFrom post processing results on graphicsscreen and graphs shown above,Displacement and stress results arediscussed as bellows:

1. Maximum stresses are observed at hubsection of rotor blade as shown in Figure 5and the stresses are found to be in safe limit.

2. Maximum stress developed at maximumspeed of 5000 rpm for Inconel, SS310A andAluminium is 67.048 Mpa, 65.684 Mpa, and22.885 Mpa respectively as shown inFigure 6.

3. From Figure 6 stresses developed in therotor increases linearly as the sameincrement of speed for different rotormaterials.

4. As the speed increases, maximum stressincreases very high in Inconel and SS310A.But the little increase of maximum stress inaluminium as speed increase.

CONCLUSIONFE structural analysis of wells turbine bladesusing Pro-E software ANSYS serves asmechanical design tool. The analyzed resultsintimated several critical blade joint betweenrotor blade and hub, which are highly stressedcausing blade failure so that joint requires

much attention and careful determination. Thevon-mises stresses are found to be in safe limitup to 5000 rpm for wells turbine. Also as thespeed of rotor is increased the stress anddisplacement also increases so for the highspeed rotor much attention is required formaterial selection.

REFERENCES1. Gato L M C, Warfield V and Thakker A

(1996), “Performance of a High-SolidityWells Turbine for an OWC Wave PowerPlant”, J. Energy Resources Technology,pp. 263-268.

2. Inoue M, Kaneko K, Setoguchi T andShimamoto K (1986b), “Studies of WellsTurbine for Wave Power Generator”, BullJSME, Vol. 29, No. 250, pp. 1171-1182.

3. Maurizio Paderi and Pierpaolo Puddu(2013), “Experimental Investigation in aWells Turbine Under Bi-Directional Flow”,Renewable Energy, Vol. 57, pp. 570-576.

4. Raghunathan S, Watterson J K, WhittakerT J J and Setoguchi T (1998), “Devicesand Turbines for Wave EnergyConversion”, 33rd Intersociety EngineeringConference on Energy Conversion,Colorado Springs, Co., August 2-6.

5. Setoguchi T, Santhakumar S, Takao M,Kim T H and Kaneko K (2003), “AModified Wells Turbine for Wave EnergyConversion”, Renewable Energy, Vol. 28,pp. 79-89.