BULLETIN OF DEFENCE RESEARCH ANDDEVELOPMENT ORGANISATION

ISSN : 0971-4413

Technology Vol. 17 No. 5 October 2009

Technology

GAS TURBINE RESEARCHAS TURBINES have become essential power plants of powerful military equipment like aircraft, naval ships and tanks. G

The required precision manu-facturing for components and temperature-resistant alloys necessary for high efficiency often makes the construction of a simple turbine more complicated t h a n p i s t o n e n g i n e s . Defence Research and Develop-ment Organisation (DRDO) is pioneering the design and development of aero and marine gas turbine engines for indigenous defence applications besides research work in the areas of aero engine sub-systems. DRDO has also established the requisite state-of-the-art testing and prototype manufacturing facilities for components and full-scale engines.

Gas Turbine Research Establishment (GTRE), Bengaluru, a constituent laboratory of DRDO, is entrusted with the design and development of Kaveri engine which is an augmented low bypass twin spool turbofan engine of 80 kN thrust class. The engine cycle is based on a detailed system analysis culminating into a potential power plant for the Indian Light Combat Aircraft Tejas. The engine incorporates flat-rated characteristics to pre-empt and mitigate the thrust drop due to high ambient intake temperature and/or high forward speed. Twin-lane full authority digital engine control with an adequate manual backup is a salient design feature of Kaveri engine.

Kaveri engines have been tested both in normally aspirated and with limited high pressure/temperature entry conditions for more than 1800 h. Stringent structural (safety and life) and aerodynamic tests have taken up as a prelude to official altitude test, flying test bed trials and accelerated mission tests leading to engine certification for airworthiness.

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KAVERI ENGINE COMPONENTS

Low Pressure and High Pressure Compressors

Annular Combustor

High Pressure and Low Pressure Turbines

Three-stage axial flow low pressure (LP) compressor has been designed with a mass flow rate of 78 kg/s; pressure rat io of 3 .4 ; i sentropic efficiency of 85 per cent; and surge margin in excess of 20 per cent. Design validation of LP compressor has been done for aerodynamic and structural tests for life and safety and the first rotor for bird impact characterisation.

Six-stage axial flow high pressure (HP) compressor has been designed for a mass flow rate of 66 kg/s; pressure ratio of 6.4; isentropic efficiency of 85 per cent; and surge margin in excess of 23 per cent. Design methodology is based on 3-D Navier Stokes code. Design validation of the HP compressor has been done for aerodynamic and structural tests for life and safety.

High intensity annular combustor has been designed for combustion efficiency greater than 99 per cent, circumferential pattern factor of 0.35 and radial pattern factor of 0.14. Design and development is based on computational fluid dynamics (CFD), empirical relations, water analogy, and aero-thermal tests at high pressure, high temperature and altitude conditions besides extensive structural analysis.

Single-stage cooled high pressure turbine has been designed for an isentropic efficiency of 85 per cent and a maximum turbine entry temperature (TET) of 1700 K. Navier Stokes codes such as TASC flow and NUMECA have been used for design and analysis. The LP turbine rotor stage is unshrouded with an isentropic efficiency of 85 per cent.

HP compressor rotor assembly

Annular combustor

HP turbine rotor assembly

LP compressor rotor assembly

Afterburner System

Engine Gearbox

Electro-Hydro Mechanical Control Systems

The afterburner system (an additional component added to some jet engines, primarily those on military supersonic aircraft) provides a thrust boost of 60 per cent over and above maximum dry thrust at an efficiency of 90 per cent, consistent light up from sea level to 11 km altitude and stability besides buzz and screech free operation. The burner has been designed using CFD tools such as FLUENT and Star-CD.

Engine gearbox (EGB) with a power rating of about 700 HP provides drive to 12 accessories of aircraft and engine in the speed range of 5600-30000 rpm. Cast out of aluminium alloy, the EGB weighs less than 57 kg. It has been tested for endurance and performance under vibration, 'g' loads, attitude, and high and low environmental temperature conditions.

Integrated nozzle actuating system (INAS) is used for actuation and control of the fully variable convergent-divergent (CD) exhaust n o z z l e t o a c h i e v e o p t i m u m e n g i n e performance (thrust and specific fuel consumption) throughout the flight envelope. I N A S c o m p r i s e s f o u r m e c h a n i c a l l y synchronised hydraulic actuators (each actuator with a load carrying capacity of 50 kN) driven by engine gearbox-mounted integrated hydraulic power pack.

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Afterburner system

Engine jet pipe with INAS and CD nozzle

Engine gearbox

Technology

Variable Geometry (VG) Actuating System has been used for varying the inlet guide vanes (IGV) and the first two stator blade angles, which control the air flow direction through the high pressure compressor for optimising the engine performance and enhancing the operability.

Main engine control unit and re-heat control unit supply the fuel to the main and re-heat combustion systems at the desired pressure and flow while ensuring smooth light up and acceleration of the engine.

All the electro-hydro mechanical control systems are interfaced with Kaveri digital engine control unit (KADECU) for proper closed loop control of the engine throughout the flight envelope.

Kaveri Digital Engine Control Unit (KADECU) is a microprocessor-based real-time embedded full authority digital control system to execute the engine control to get optimum thrust within safety limits. Two such units have been mounted on the Kaveri with one under control and the other in hot standby mode. KADECU performs extensive built-in test and sensor data validation to detect failure and record off-line analysis. Real-time monitoring allows acquisition of data from the control units and enables the study of the control system performance vis-à-vis the engine behaviour.

GTRE has set up extensive structural test facilities for structural integrity and life evaluation of various components and sub-systems such as fan/compressor/turbine rotor discs and blades, transmission shafts, casings, piping, engine gearbox, etc.

Kaveri Digital Engine Control Unit

STRUCTURAL TEST FACILITIES

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Kaveri engine control unitdigital

Cyclic spin test facility is used for low-cycle fatigue life evaluation of engine rotor discs and incorporates fully automated motor-driven system capable of providing variable speeds. This facility simulates various combinations of speed and temperature.

Torsional test facility is used to evaluate fatigue life of rotor shafts under simulated torsion, axial, and temperature load conditions. The facility is capable of applying desired load profile along with minor cycles superimposed.

Dynamic foreign body impact test facility is used for impact tests with simulated bird models fired at various speeds on rotor blades, disc and casings. It comprises a compressor air operated bird g u n a n d h i g h - s p e e d photography cameras for monitoring the tests, both

under static and dynamic conditions.

Full-scale power absorption test facility is used for performance and endurance testing of engine accessory gearbox along with various Line Replaceable Units (accessories) mounted and duly loaded using water brake dynamometer.

Attitude testing is performed to validate the design of Kaveri's gearbox under attitude conditions experienced during the flight, including inverted flights also. Gearbox internals experience both oil starvation and oil flooding depend-ing on attitudes. Performance evaluation of the lubrication system is the point of focus during the subject test.

The casing structural test facility equipped with fatigue-rated actuators is used for structural integrity assessment of engine frames, rotor-support structures, and engine-mount points. The system facilitates programming of desired load spectrum, execution and monitoring of the tests in both static and dynamic modes.

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Dynamic foreign body impact test facility Full-scale power absorption test facility

Cyclic spin test facility Torsional test facility

Attitude test facility Casing structural test facility

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AERODYNAMIC TEST FACILITIES

GTRE has established in-house facilities for aero-thermodynamic performance evaluation of critical modules such as fan, compressor, turbine, combustor, and afterburner. These facilities are equipped with extensive instrumentation and data acquisition systems for online monitoring as well as analysis.

Compressor test facility is used to evaluate the performance of fan and compressor modules, both under design and off- design conditions.

Combustor test facility is used for evaluation of combustor system performance, both under design and off-design conditions of pressure, temperature and air flow.

Cold turbine test facility is used for evaluation of turbine module performance, both under design and off-design conditions of pressure, temperature and air flow. It employs an electro-hydraulic dynamometer for power absorption.

Afterburner test rig is used for test and evaluation of scaled-down model of engine afterburner, both under simulated screech and buzz conditions with several pilot ignition system configurations.

Compressor test facility Combustor test facility

Cold turbine test facility Afterburner test facility

ENGINE TEST FACILITIES

SIMULATION AND ANALYSIS FACILITIES

GTRE has set up four engine test cells for normally aspirated condition and one test cell capable of simulating inlet flight conditions up to 0.4 Mach for carrying out performance tests.

Test cells are designed for normally aspirated testing (thrust up to 20,000 kg) and capable of carrying out engine testing with afterburner system (exhaust gas temperature of >2000 K).

Salient Features

Acoustically attenuated vertical intake and exhaust systems.

Roof-mounted thrust stand with off-line thrust calibration.

Data Acquisition System (DAS) with provision of 1200 channels.

Test cells for engine bleed and power off -take.

Customer bleed measuring facilities and emergency fuel supply.

GTRE has also set up extensive simulation and analysis facilities to enable design evaluation, prototyping, digital manufacturing, optimisation and assembly integration. These facilities consist of high-end hardware, and in-house and commercial software tools.

GTRE has a computer-aided design and virtual reality laboratory for carrying out designing and validation tests. 3-D CAD modelling of Kaveri for finite element analysis, mass property calculations, assembly integrity evaluations, automated drafting, rapid prototyping and digital assembly manuals preparation, and enhanced visual feel of the components and virtual walkthrough of assemblies were done at this laboratory.

Computer-aided Design and Virtual Reality Laboratory

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Engine mounted in test cell

Engine test data acquisition system

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Computer-aided Engineering

Computational Fluid Dynamics

The computer-aided engineering facility is being used for the following:

Structural design analysis of gas t u r b i n e c o m p o n e n t s u s i n g NASTRAN, ANSYS, ABAQUS, LS-DYNA and SAMCEF software.

Kinematic design analysis of variable CD nozzle and compressor variable guide vane linkage mechanisms for aero-engine.

Development of whole engine model, engine static, dynamics and blade-off simulation.

L i f e p r e d i c t i o n o f e n g i n e components employing in-house practices and material characteri-sation.

Methodology for life extension of aging engine components.

Damage tolerance analysis of the gas turbine components. Design and development of composite structures.

Computational fluid dynamics (CFD) codes have been used extensively for the design and analysis of aero and marine v e r s i o n s o f K a v e r i e n g i n e modelling, CAD grid generation and high performance compu-ting form integral features of the CFD and conjugate heat transfer (CHT) analyses.

The parellel CFD software like CFX TASC Flow, FLUENT, NUMECA have been used for designing and analysis of the engine compo-nents.

Structural analysis of various components

Combustion flow analysis Turbine flow analysis

The following are the salient features of the CFD analysis:

Estimation and improvement of aerodynamic performance of all the major modules and sub-systems of the engine, viz., fan, compressor, combustor, turbine, afterburner with CD nozzle and bypass duct.

Estimation of the liner metal temperatures of hot-end components through CHT analyses.

Estimation of the secondary air temperature rise while passing through the compressor and turbine annular disc through CHT analyses.

GTRE has extensive manufacturing facilities consisting of CNC systems (machining centre, EDM wire cut and vertical turn mill centre), investment casting, electron beam welding, vacuum heat treatment, jig boring, etc. Besides, quality assurance and inspection facilities consisting of 3-D CMM, x-ray diffraction, ultrasonic testing, non-contact 3-D scanning system, x-ray fluorescence spectrometer, and hard bearing balancing are also being used to maintain high standards of the products.

MANUFACTURING, PROTOTYPING AND QUALITY CONTROL FACILITIES

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3-D CAD model Computational grid Tip clearance flows

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RAPID PROTOTYPING

This scaled engineering prototype of Kaveri engine has been prepared using rapid prototyping technologies of stereolithography and fused deposition modelling using 3-D CAD model data. The entire sequence of prototyping activities include pre-processing, part building, post-processing, assembly and mounting.

KAVERI MARINE GAS TURBINE ENGINE

The Kaveri Marine Gas Turbine (KMGT) engine, a derivative of Kaveri aero engine, is also being developed as a power plant for propelling Indian naval ships. The gas generator of KMGT is derived from Kaveri aero engine, and a two-stage free power turbine has been designed to translate the gas power into mechanical output to drive the ship propeller.

Salient Features

Output : 15 MW at ISA-SLS

Specific fuel consumption : 0.27 kg/kW-h at ISA-SLS

Fuel : Low sulphur high speed diesel (LSHSD)

Power turbine speed : 5800 rpm

TET : 1560 K (max)

KMGT engine has successfully demonstrated output power and SFC exceeding the specification. Spin test of power turbine disc has been carried out using dummy blades simulating the centrifugal load. Forty hours of test has been successfully completed at maximum rated speed of power turbine, thereby demonstrating the mechanical integrity of power turbine disc assembly.

GTRE has implemented Product Lifecycle Management (PLM) framework for the design and development of Kaveri and its derivatives. Team centre suite of product was used for PLM implemen-tation with customisation for product design, configuration management, change management, CAD management, and programme management. High performance computing facility (P 690) and ESS800-based data centre from IBM forms the core hardware infrastructure.

PRODUCT LIFECYCLE MANAGEMENT

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11High performance computing facility (P 690)

Spin test facility

Technology

Dr AL Moorthy, Director, DESIDOC, Metcalfe House, Delhi

Dr BR Gandhe, Director of Armaments, DRDO

Director of Materials, DRDO

Shri R Shankar, Director of CV&E, DRDO Bhavan, New Delhi

Director of Naval Research & Development

DRDO

Shri Ranjit Elias, SO to SA to RM, DRDO Bhavan, New Delhi

Coordinator

Members

Bhavan, New Delhi

Dr Sudarshan Kumar, Bhavan, New Delhi

Cmde PK Mishra,

Bhavan, New Delhi

lEikndh; eaMy Editorial Committee

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àÉxÉÉäVÉ BÉÖEàÉÉ® cÆºÉ BÉÖEàÉÉ® Editor-in-Chief Assoc. Editor-in-Chief Editors Editorial Assistant Printing DistributionAL Moorthy Shashi Tyagi B Nityanand Dipti Arora SK Gupta RP Singh Manoj Kumar Hans Kumar

Printed & published by Director, DESIDOC, on behalf of DRDO

Air mass flow : 78 kg/s

Kaveri Engine—Salient Features

By-pass ratio : 0.2-0.24

Overall pressure ratio : 21.5

Turbine entry temperature (flat-rated) : 1487-1700 K

Maximum thrust (dry)-IRA, SL : 52 kN

Maximum thrust with afterburner-IRA, SL : 81 kN

SFC (dry) : 0.78 kg/h/kg

Maximum SFC with afterburner : 2.03 kg/h/kg

Thrust/weight ratio : 7.8