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ANALYSIS OF TURBOMACHINE BLADES - A REYIEW

V. Raroamurti* and P. Balasubntnajuan**

Abstract. This literatur* raviaw daa/s with the static and dynamie analysis of turbina bladas and diacs. The yarious formulatbns and ao/utbns of linaar and nom linaar vibrations of bladas and diacs ara summarizad. Exparimantai mathods ara aiao diacuuad.

simple formułas are available for the determjnation of bending moment components in the blade (8. 9). A Computer program for the three-dimensional stress analysis of a blade using the finite element method is available (10).

Hundreds of articles have been published concerning the dynamie behavior of turbinę blades. In this paper references published mostly between 1979 and 1983 are reviewed in the fields of stress and vibration analy9es of blades and blade-disc interactions and experimental methods. This review includes both experimental and analytical investigations.

BLADES

Stress Analysis of Blades

Durocher and Kane (1 ] investigated blade deflections with a uniformly pretwisted finite element beam model. They checked prevk>usly obtained results with predictions from a three-dimensional finite element analysis; included were the effects of shear stress, axial-torsional coupling, and torsional stiff-ness. An analytical procedurę based on the finite element method (FEM) was used to determine the blade stresses and deflections [2]. Ramamurti and Sreenivasamoorthy (31 used a three-dimensionał 20 noded isoparametric finite element to analyze the rotating blade stresses for various pretwist angles, skew angles, breadth to length ratios, and breadth to thickness ratios of the blade. They compared these results with experimental results.

Blade loading for the input forces has been investi-gated with a NASTRAN finite element model (4]. Blade failures due to stresses have also been studied [5]. Stresses at the boundary of a blade have been predicted (6, 7) using elliptical equations and the successive approximate method. Nomograms and

Vibration Analysis

Linaar analysis. Several references are available on linear analysis (11-14). Leissa (12-14] discussed tne merits and disadvantages of beam theory, piąte theory. and shell theory with numerical results. In most recently published articles FEM has been used to $olve blade vibration problems. The dynamie strength of group of blades has been investigated by considering the blade as a finite element beem model (15). One vibration study of rotating beem included the effects of root radius, setting angle. and tip mass in the finite element model (16). A triangu-lar Shell element model has also been used (17). The results of this analysis showed the effects of geo metric stiffness, rotational effects. aspect ratio. pretwist, taper. skew angle. and disc radius. Thomas and Sanbunch (18l extended finite element analysis to the behavior of rotating pretwisted blades of asym-metric cross section. Redesigning the vibrational characteristics of the blades was done with a NASTRAN program (19). Variations due to transverae shear deformation and rotary inertia were pointed out (20).

A simple and powerful procedurę has been used to calculate the frequencies of shallow shells (21). A superparametric shell element is available to predict the vibrational characteristics of a real blade [22]. Yargicoglu (23) studied a substructure technique for composite rotor blades. The dynamie response of blades with a weighted edge has been analyzed for different end conditions and radii of curvature with the help of curved cylindrical finite elements (24). Forced vibration analysis using a substructure tech-nigue has been implemented for rotating structures

of Technology, Madret-600036, Indie Inttłtute of Technology, Madrae 600036, Indie

'Profmaor, Department of Applied Machanie*, Indian Inttłtute ••Peteerch Scholar. Department of Applied Machania, Indian

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