ANALYSIS OF REPAIRED GAS TURBINE AND COMPRESSOR BLADES

-Abstract. In order to reach desired levels of efficiency and power output of jet engines, advanced gas turbine and compressor blades made from Ti-6AL-4V alloy operate at very high temperatures (up to 600°C) and speeds (up to 10000 rpm) [3–4]. Pressure of springing streams and inertial forces are main reasons of stress appearance in the blades. Besides that, blade usually could be out of action after one’s edges had become damaged under temperature or foreign object hit negative influence. High cycle fatigue (HCF) accounts for 56 % of major aircraft engine failures and ultimately limits the service life of most critical rotating components. Extensive inspection and maintenance programs have been developed to detect, renew and replace defected blades, to avoid catastrophic engine failure. Various modern technologies including laser cladding (filling layers of sprayed material) allow prolongation of blades’ life by damaged part’s renovation with alternate material. The general aim of the present work concludes of blades’ mechanical bahavour comparison before and after renewal.


Introduction
To solve the problem, separately have been researched two kinds of blades: compressor and turbine blades, which both are used as parts of differing aero jet engines (Figs 1, 2). On the occasion of that, the 3-Dimension parametric models of mentioned blades were created by SolidWorks software foundation using scanned and measuring information. Original sampled and renewed blades' mechanical behavour comparison consisted of stress-strain state analysis for origin and repaired damage-simulated blades using SolidWorks and it's integrated module CosmosWorks software [1]. As results of finite element analysis(FEM) Von Mises equivalent stresses and displacements for all overlooked models have been obtained.

Preparing for calculation and the experiment
To make certain about conformity of models and the original samples, the first calculation step included own frequency determination and their comparison with experimental results. An experimental frequency value responce had been received with the help of Polytec PSV-400 laser vibrometer system before other analysis started. Its modular design allows the frequency, velocity and displacement capabilities to be tailored to specific or multiple applications. Both analogue and digital decoders are available, giving a frequency range from near DC to 20 MHz, with velocities to ± 10 m/s and displacements from the sub-nanometer to meter range. A vibrometer system is comprised of controller electronics and a noncontact standard-optic or fiber-optic sensor head. The controller provides signals and power for the sensor head, and processes the vibration signals. These are electronically converted by specially developed decoders within the controller to obtain velocity and displacement information about the test structure. This information is provided by OFV-5000 in either analog or digital form, for further data evaluation.  The continuation of modeling was directed to possible blades' defects simulation [7]. Damaged side and upper edges for 5, 10, 15 millimeters and 5, 15, 30 millimeters accordingly, as also dents in frame were filled up with alternate material alloy -Inconel Alloy 718 [2]. Main differences between initial and welded alloys are focused on module of elasticity and thermal conductivity disparities are shown in the table [5][6]. Overlooked

Stress-strain analysis
Performed task implied consideration of an external air and gas laminar streams and their influence over the rotating blades, as well as taking in account internal turbo-blades cooling by flowing channels inside them. Applied thermal condition and flow rate data was passed by the integrated module of CosmosWorks software. Besides that, the interaction between blades' allowance in the turbine and compressor has been examined applying European standard by three blades, fixed in the rotor one by one. The middle blade was under primary attention. After all finite element models had been obtained, Von Mises equivalent stress determination got under way. Used Von Mises equivalent stress formula is brang lower, where τ is tangential strain in indicated planes: General analysis of compressor blade was concentrated on three blades combination model, while turbine blade was looked over as single object [8]. Nondamage variant of compressor blades acquiring proper conditions (flow rate, temperature, loads) was examined first. Expected main stress concentration, as well as maximum stress value for whole researching model due tue great inertial forces appeared in the blades' bottom part, where blade's "wing" connects crown. That tendence was typical for all overlooked models.
The goal contained in material replacement influence over the stress value increase in object's volume, therefore were made results' gathering from the origin and replaced material part's border place.

Conclusions
So as to get optimal power output of jet engine, all compressor and turbine blades have to be trig and function properly. From the economical point of view, to renew damaged blades is much favourable than to replace them by new ones. This work' s general aim was to compare differences between original and renewed objects' equivalent Von Mises stress -strain values, which appear in the blades at the same working conditions. From reached results following pattern can be concluded:as bigger damage is repaired and accordingly more alternate material (with bigger specific gravity and thermal ex-pansion) is placed in the object, as larger stress values are got in the result.