Numerical Analysis of Flow through Shrouded Turbine ... - IRD India

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)this mesh is considered to be the best. This meshformation was done with GAMBITIII. RESULTS AND DISCUSSIONA. Pressure Coefficient Of Turbine BladesThe pressure coefficient of over the blades of theturbine rotor stage is shown in the figure-5. The turbinerotor stage consists of 43 blades arranged with theangular orientation of 8.73 degrees between each blade.From the figure-5 it is observed that, the pressurecoefficient is maximum at the leading edge of the bladewhich represents the stagnation point of the blade. Thepressure coefficient is minimum at the suction sidewhich represents the velocity is maximum at thatlocation.6. From the figure, it is observed that, the pressurecoefficient is maximum at the leading edge of the bladewhich represents the stagnation point of the blade. Thepressure coefficient is minimum at the suction side andnear the trailing edge which represents the velocity ismaximum at that location.The contour of pressure coefficient on the suctionside of the blade is shown in the figure-7. It is observedform the contour that the pressure coefficient isminimum and there is a small variation in the pressurecoefficient near the hub and shroud of the blade, due toend wall boundary layer formation and wake formationbecause of the highly curved surface of the blade. Thecontour of pressure coefficient on the pressure side ofthe blade is shown in the figure-8.Fig. 5 pressure coefficient distribution along the spanof the bladeThe pressure coefficient variation along the span ofthe blade is plotted in figure-5. It is observed thepressure coefficient decreases near the hub and shroudof the blade. It is observed that the decrement in thepressure is due end wall boundary layer creation nearthe hub and shroud of the blades.Fig. 7 : Pressure Coefficients on Suction Surface of theBladeFig. 6: Pressure Coefficient at the Mid-Section of the BladeThe pressure coefficient variation over the bladesurface at the midsection of the blade is shown in figure-Fig. 8 : Pressure Coefficient On The Pressure SurfaceOf The BladeIt is observed form the contour that the pressurecoefficient is higher than that of suction side and there isa small variation in the pressure coefficient near the huband shroud of the blade, because of end wall boundarylayer formation and wake formation because of thehighly curved surface of the blade.3ISSN : 2319 – 3182, Volume-2, Issue-3, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)B. Cascade Analysis Of Turbine Blade PressureCoefficients On Surface Of BladeThe pressure coefficient variation over the cascadedblade surface at the midsection of the blade is shown infigure-9. From the figure, it is observed that the pressurecoefficient is maximum at the leading edge of the bladewhich represents the stagnation point of the blade. Thepressure coefficient is minimum at the suction side andnear the trailing edge which represents the velocity ismaximum at that location.Fig. 9 : Pressure Coefficient On The Cascaded Blade SurfaceThe contour of pressure coefficient on the pressureside of the blade is shown in the figure-10. It is observedform the contour the pressure coefficient is minimum atthe center of the blade because of wake formation on theblade and there is a small variation in the pressurecoefficient near the hub and shroud of the blade,because of end wall boundary layer formation on thesurface of the blade. The contour of pressure coefficienton the suction side of the blade is shown in the figure-10. It is observed form the contour the pressurecoefficient is lower than that of pressure side and thereis a small variation in the pressure coefficient near thehub and shroud of the blade, because of end wallboundary layer formation and wake formation becauseof the highly curved surface of the blade.Fig. 10(b) : Cp distribution on pressure surfaceC. End Wall Boundary Layer Separation On CascadedBladesEnd-wall loss is also known as secondary loss, andis related to the passage and the horseshoe vortices. Dueto these loses, the pressure coefficient near the hub andshroud of the blade decreases as shown in the figure-11.Fig. 10(b) : Cp distribution on suction surfaceFig. 11 : End Wall Boundary Layer SeparationD. Leakage Analysis Through Shroud Z-Gap PressureCoefficients On Surface Of BladeThe pressure coefficient variation over the surfaceof shrouded turbine blade with 2mm z-gap at the midsectionof the blade is shown in figure-12. From thefigure, it is observed that, the pressure coefficientdecreases on the suction side of first blade because ofthe gap between shrouds.4ISSN : 2319 – 3182, Volume-2, Issue-3, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)Fig. 12 : Pressure Coefficient of shrouded blade with2mm z-gap (mid-section)Due to the gap near the shroud, the end wallboundary layer separation decreases as shown in thepressure coefficient contour in figure-13. The first figshows the Cp contour on pressure surface and second figshows the Cp contour on suction surface.Fig. 13 Cp distribution on blade surfaceE. Comparison Of Shrouded Blades With Gap AndWithout GapFrom the above fig 14 it is observed the pressurecoefficient on pressure side of blade 1 lowers because ofthe large end wall boundary layer formation on thecascaded blades without gap but on the shrouded bladewith 2mm gap the pressure coefficient is same as that ofthe reference pressure. It is also observed the pressurecoefficient on suction side of blade 1 increases due tothe large end wall boundary layer formation on thecascaded blades without gap but on the shrouded bladewith 2mm gap the pressure coefficient is same as that ofthe reference pressure. Thus due to 2mm z-shroud gapon the turbine blades shrouds the end wall boundarylayer is reduced by the leakage of primary airflowthrough the 2mm gap between the shrouds.Fig. 14: Cp Of Blade With Gap And Without GapIV. CONCLUSIONThe effect of the turbine rotor blade shroud z-gapon the pressure coefficient distribution on the surface ofthe blades is analysed. It is found there is decrease in thepressure coefficient near the shroud of the turbine blade.Although there is a decrease in the pressure coefficienton the surface of the blade but it reduces effect of endwall boundary layer separation near the shroud of theturbine blade because of the leakage of primary flowthrough the gap between the shrouds.V. FUTURE WORKThe present computational work has to carried outon the models with different shroud gaps such as 0.25mm, 0.5mm, 0.75mm, 1mm, 1.25mm, 1.5mm and1.75mm to find out the optimum gap size for betterperformance of the blade in the engine. Experimentalwork has to be done by creating the model and analyzethe model with the same conditions as that ofcomputational analysis. The experimental results can beanalyzed with the computational results for verificationof results. If both the results are same it can beimplemented in turbine engines for various applicationsVI. REFERENCES[1] Villiers, J. D., & Govender, S. (2003). validationof a CFD Static Pressure Distribution againstExperimental Data for a Turbine. R & D Journal,19(3), 3–5.[2] Ameri, A. A., Park, B., & Steinthorsson, E.(1996). Analysis of Gas Turbine Rotor andShroud Heat Transfer Blade Tip (p. 10).[3] Maier et al, inventor; 1991 Jan.11. Gas turbineblade shroud support. United States patent US5,022,816.5ISSN : 2319 – 3182, Volume-2, Issue-3, 2013