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John S.K.,Regional Center for Military Airworthiness Engines | Mishra R.K.,Regional Center for Military Airworthiness Engines | Shetty B.P.,Nitte Meenakshi Institute of Technology
Journal of Failure Analysis and Prevention | Year: 2017

Repair schemes for rectification of deviation and or defects in a turbo-shaft engine have been undertaken for sustaining reliability and availability of airborne equipments. A number of reclamation schemes have been developed and implemented successfully. This paper describes the common defects encountered in the aeroengine under study. The methodology for developing the reclamation scheme has been presented along with few case studies. These schemes have helped in maintaining the fleet effectively and avoiding costly rejections and turnaround time of the aeroengine. © 2017 ASM International


Mishra R.K.,Regional Center for Military Airworthiness Engines | Muduli S.K.,Regional Center for Military Airworthiness Engines | Srinivasan K.,Hindustan Aeronautics Ltd Engine Division | Ahmed S.I.,Aeronautical Quality Assurance Engines
Journal of Failure Analysis and Prevention | Year: 2015

Failure of an inter-shaft bearing in an aero gas turbine engine is investigated to determine its root cause. Teardown inspections followed by metallurgical investigations are carried out on the parts of the failed bearing. None of the components of the bearing has shown any discolouration, wear, or overheating marks. But severe flaking is observed on one side of the outer raceway. It indicates progressive fatigue due to overload. Insufficient clearance due to differential expansion of inner ring and contraction of outer ring due to heating and cooling, respectively, can also result in this type of phenomena. Maintaining oil discipline and using correct grade of oil at proper frequency can address these issues. A comprehensive engine-bearing prognostic approach may be followed utilizing available sensor information on-board the aircraft such as rotor speed, vibration, lube system information, and aircraft maneuvers to predict bearing life and incipient bearing failure. © 2015, ASM International.


Dileep S.,Aerospace Engine Research and Development Center Hindustan Aeronautics Ltd | Esakki Muthu S.,Aerospace Engine Research and Development Center Hindustan Aeronautics Ltd | Udayanan P.,Aerospace Engine Research and Development Center Hindustan Aeronautics Ltd | Mishra R.K.,Regional Center for Military Airworthiness Engines
Journal of Failure Analysis and Prevention | Year: 2015

The rotating gas turbine engine component such as centrifugal compressor is subjected to various static and dynamic loads during service. These service loads introduce multiaxial stress-strain states and inflict severe structural damage and hence reduce compressor efficiency and service life. In many cases, the service loads are non-proportional which introduces additional cyclic hardening depending on the loading path and the material used (Wu et al., Int J Fatigue 59:170–175, 2014). Studies have revealed that fatigue life is drastically reduced as a result of this additional cyclic hardening phenomenon. In recent decades, numerous multiaxial fatigue damage theories (which are strain based) have been developed taking into account the factors influencing fatigue like operating temperature, anisotropy, microstructure, nature of loading (proportional or non-proportional), and environmental effects. In general, these theories envisage crack nucleation and propagation to take place at a critical plane, but differ from one another the way critical planes are defined and damage parameters are proposed. To estimate the fatigue life under the multiaxial loading conditions, these theories relate multiaxial stress-strain components to uniaxial fatigue properties obtained from test data. But, it is observed that most of these theories are limited in application to a particular material or loading conditions. No general consensus is available on the best available fatigue damage theory for a particular application. Further, literature shows that most of these theories are applied and compared on tubular and notched test specimens under proportional and non-proportional loading conditions. Literatures are seldom available which compares these theories at the application level and validate through experiments. The objective of this paper is to estimate the low-cycle fatigue life of a centrifugal impeller used in a gas turbine application using different multiaxial fatigue damage models in the literature and propose a methodology which closely fits the experimental results. For applications such as gas turbine engines, the margin of safety (with respect to 0.2% PS) varies in the range of 1.05 to 1.15 (Stephens et al. in Metal fatigue in engineering. Wiley, New York, 2001). For this, it is extremely important to estimate the life and damage mechanism affecting the life of the components accurately to ensure the flight safety, reliability, and total service life of the gas turbine engine. The centrifugal impeller was designed for a pressure ratio of 3.2 and maximum rotational speed of 52,500 rpm. The titanium alloy Ti6Al4V was chosen as the possible material for the impeller as it has high strength and stiffness to weight ratio and is widely used in aerospace application (Wu et al., Int J Fatigue 44(12):14–20, 2012). The entire analysis can be divided into three main modules. Firstly, the stress and strain history on the centrifugal impeller was determined under actual operating condition. Finite element structural analysis packages were used for this purpose. Secondly, the stress-strain histories obtained from FE analysis were post-processed using several multiaxial fatigue damage models like Maximum von Mises strain model (Kalluri and Bonacuse in In-Phase and Out-of-Phase Axial-Torsional Fatigue Behavior of Haynes 188 at 760 °C. NASA Technical Report 1991, 91-C-046, 1991), which is based on the equivalent strain and the Smith-Watson-Topper (SWT) model (Shamsaei and McKelvey, Int J Fatigue 59:170–175, 2014), Kandil-Brown-Miller (KBM) model (Kandil et al., Met Struct 280:203–210, 1988), Fatemi and Socie (FS) model (Fatemi and Socie, Fatigue Fract Eng Mater 11(3):149–166, 1987), which are based on the critical plane approach to obtain the fatigue life. Finally, a prototype of the centrifugal impeller was made and tested at our sophisticated cyclic spin test facility to validate the Low-Cycle Fatigue life. © 2015, ASM International.


Mishra R.K.,Regional Center for Military Airworthiness Engines | Thomas J.,Hindustan Aeronautics Ltd
Journal of Failure Analysis and Prevention | Year: 2014

During altitude maneuver loud bang sound was observed followed by rapid winding down of engine rotation and jet pipe temperature. Compressor casing top half was found severely ruptured and broken into many pieces. On viewing through the ruptured area compressor rotor blades were found sheared at the root. Systematic investigation revealed that the failure of compressor casing was due to sudden overload. Analyzing the possible reasons of sudden overload it could be concluded that the rupture of compressor casing was most probably due to surge during the maneuvers. Remedial measures are suggested to address such failures. © ASM International 2014.


Mishra R.K.,Regional Center for Military Airworthiness Engines
Journal of Failure Analysis and Prevention | Year: 2015

This paper deals with the study carried out on fouling and corrosion problems in an aero gas turbine engine which operates from coastal environment. Various parameters responsible for such problems are presented in the paper which causes deterioration in performance and leads to failure of the components. Prevention and control procedures for fouling and corrosion are also highlighted. Compressor washes such as performance recovery wash and desalination wash are found to be very effective in addressing these issues. The frequency of compressor wash is to be judiciously worked out from the corrosion rate and performance deterioration points of view. © 2015, ASM International.


Mishra R.K.,Regional Center for Military Airworthiness Engines | Prakash L.,Regional Center for Military Airworthiness Engines | Mistry S.N.,Regional Center for Military Airworthiness Engines
Journal of Failure Analysis and Prevention | Year: 2015

A multistage high-pressure compressor drum has been designed for a low bypass military turbofan engine. The complex mission profile of the engine with high throttle excursion demands reliable operation of the compressor throughout the flight envelope maintaining structural integrity. Therefore, qualification of the compressor drum for a fighter class engine is a challenge from the airworthiness point of view. This paper presents the methodology adopted and various stages of qualification, standards followed, and results based on which clearance has been accorded for fitment in engine and engine on aircraft. The compressors thus fitted in engine have exhibited satisfactory performance and are at different stages in service. © 2015, ASM International.


Mishra R.K.,Regional Center for Military Airworthiness Engines | Kishorekumar S.,Gas Turbine Research Establishment | Chandel S.,Indian Defence Institute of Advanced Technology
Journal of Failure Analysis and Prevention | Year: 2015

Flame blow-out is a serious concern for military gas turbine engines, and maintaining a reliable and stable flame in engine throughout the mission is a great challenge. A low bypass military turbo fan engine is investigated for flame blow-out. The history of the engine and its accessories were reviewed. Flight data were analyzed to confirm the blow-out incident. Air flow passages and engine modules were examined for possible foreign object damages or internal damages and found satisfactory. Analysis of atomizer characteristics showed the shifting of spray cone angle and fuel flow rate close to the lower limits. Blockage of atomizer flow passages and liner front end flares could contribute to flame blow-out. One of the filters in the fuel line found damaged. Significant amount of debris were found inside the fuel control valve. From the investigations and evidences, it was concluded that the engine flame blow-out was due to blockage of fuel flow when the air flow was almost steady. Assessment and control of debris in fuel accessories, the periodicity of inspection, and cleaning are very important for maintaining a stable flame throughout the mission. Also understanding the blow-out mechanism in an aero gas turbine engine during maneuvers is necessary to address blow-out issues. © 2015, ASM International.


Mishra R.K.,Regional Center for Military Airworthiness Engines | Beura C.,Hindustan Aeronautics Ltd
Journal of Failure Analysis and Prevention | Year: 2014

This paper deals with the performance study and life consumption assessment of a long range civil aircraft engine with respect to take-off variables like airport altitude, ambient temperature, thrust levels, and flight duration. The component selected for lifing analysis is the first stage high pressure turbine blade/disk of a 430 kN thrust engine. Performance tools like TURBOMATCH and HERMES are validated against the published data, with deviation less than 4%. Based on failure modes like low cycle fatigue, creep, and oxidation, the integrated lifing tool is used to estimate the severity indices at various offdesign conditions. It is observed that creep is the main criteria in blade failure due to extreme high temperature gas coming from combustor, whereas for disk it is fatigue due to repeated stresses with varying shaft speeds. With increase in airport altitude, the blade and disk severity increases with respect to that at sea level conditions. As the ambient temperature goes up, blade severity also increases as well but the change in disk severity is not as much due to less change in spool speed. Operating with reduced thrust, both the blade and disk severity decreases with deratings. As flight duration increases with reference to a standard mission, both the component damages go up but the blade severity is more pronounced than the disk due to exposure to high temperature for a long time. As a whole, the total damage severity of disk and blade assembly increases with rise in altitude, outside air temperature, and mission duration and decreases with engine deratings. © ASM International 2014.


Mishra R.K.,Regional Center for Military Airworthiness Engines | Kumar S.K.,Gas Turbine Research Establishment | Chandel S.,Indian Defence Institute of Advanced Technology
International Journal of Turbo and Jet Engines | Year: 2016

Effect of fuel spray cone angle in an aerogas turbine combustor has been studied using computational fluid dynamics (CFD) and full-scale combustor testing. For CFD analysis, a 22.5° sector of an annular combustor is modeled and the governing equations are solved using the eddy dissipation combustion model in ANSYS CFX computational package. The analysis has been carried out at 125 kPa and 303 K inlet conditions for spray cone angles from 60° to 140°. The lean blowout limits are established by studying the behavior of combustion zone during transient engine operation from an initial steady-state condition. The computational study has been followed by testing the practical full-scale annular combustor in an aerothermal test facility. The experimental result is in a good agreement with the computational predictions. The lean blowout fuel-air ratio increases as the spray cone angle is decreased at constant operating pressure and temperature. At higher spray cone angle, the flame and higherature zone moves upstream close to atomizer face and a uniform flame is sustained over a wide region causing better flame stability. © 2016 by De Gruyter.


Mishra R.K.,Regional Center for Military Airworthiness Engines | Raghavendra Bhat R.,Hindustan Aeronautics Ltd | Chandel S.,Indian Defence Institute of Advanced Technology
International Journal of Turbo and Jet Engines | Year: 2015

A case of compressor surge with bang noise during takeoff roll is investigated and presented in this paper. Fatigue failure of compressor rotor blades during takeoff is found to disturb the aerodynamics of compressor flow causing the surge. Based on evidences, failure of rotor blades and compressor surge due to over-speed and foreign object debris is ruled out. The paper presents the methodology adopted for the investigation and also suggests remedial measures necessary to prevent such incidents.

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