- •Foreword
- •Предисловие
- •Chapter 1. Introduction
- •From the history of aeroengines development. Classification of air gas turbine engines
- •Table 1.1
- •Table 1.2
- •1.2. Design features of manifold types of gas turbine engines
- •Main specifications for some serial turboprop and turboshaft
- •Fig. 1.3. Principal scheme of a two-shaft afterburning
- •Fig. 1.4. Principal scheme of a two-shaft tfe
- •Fig. 1.5. Principal scheme of a three-shaft tfe
- •Fig. 1.8. Principal scheme of a tpfe with a coaxial propfan
- •Main stages of gas turbine engines creation
- •1.4. Absolute and specific parameters of gas turbine engines
- •1.4.1. Absolute and specific parameters of turbojet engines
- •1.4.2. Absolute and specific parameters of turboprop engines
- •I.5. Air gas turbine engine’s lives
- •1.5.1. Nomenclature of lives
- •1.5.2. Sequence of assigning, setting and increase of lives
- •1.5.3. General requirements to life testing of engines and their main elements
- •1.5.4. Forming of test cycles
- •1.5.5. Forming of programs of life tests
- •Questions for self-check
- •2.1. Types of loads acting upon gas turbine engine structural elements
- •2.1.1. Classification of loads
- •2.1.2. Gas loads
- •2.1.3. Mass (inertial) forces and momenta
- •2.1.4. Temperature stresses
- •Fig. 2.4. For determination of the centrifugal forces
- •Fig. 2.5. For determination of the disc temperature stresses
- •2.1.5. Concept of dynamic loads
- •Fig. 2.9. Gas flow velocity behind nozzle vanes
- •2.2. Axial gas forces coming into action in gas turbine engines. Formation of thrust in gas turbine engines of manifold types
- •2.2.1. Axial gas forces acting on the basic gas turbine engine units
- •Fig. 2.10. Scheme of axial forces acting on basic gte units
- •2.3. Determination of axial gas force acting on impeller of gas turbine engine centrifugal compressor
- •2.4. Torques coming into action in gas turbine engines. Balance of torques
- •In gas turbine engines
- •2.4.1. Torques in turbine and compressor
- •Fig. 2.14. For determination of turbine rotor wheel torque
- •2.4.2. Torque balance in gas turbine engines of manifold types
- •Questions for self-check
- •Engine blades
- •Loads acting on blades. The blade stressed state characteristic
- •Fig. 3.1. Loads acting on the blade (a) and the scheme of blade loading
- •Determination of rotor blade tensile stress caused by centrifugal forces
- •The design scheme
- •3.2.2. Equation of a rotor blade stressed state
- •Integrating equation (3.3) in view of the ratio (3.1), we will get
- •3.2.3. Calculation of tensile stress at manifold laws of change of blade section area along its length
- •If the blade section area decreases from the root to periphery under the linear law:
- •In this case an integration by formula (3.7) yields
- •Determination of rotor blade bending stress caused by gas forces
- •3.3.1. Design scheme of a blade
- •3.3.2. Determination of gas load intensities
- •Determination of the bending momenta in axial and circumferential planes
- •3.3.4. Determination of the blade section geometrical characteristics
- •Determination of bending stress caused by gas force
- •Determination of rotor blade bending stress caused by centrifugal forces
- •The design scheme
- •3.4.2. Equation of the bending momenta
- •3.5. Guide and nozzle diaphragm vanes strength calculation features
- •3.5.1. Console type vanes
- •3.5.2. Double-support vanes
- •3.5.3. Frame type vanes
- •3.6. Evaluation of gte rotor blades strength
- •3.6.1. Grounding of blade stressed state criterion
- •3.6.2. Estimation of the blade temperature
- •3.6.3. Determination of blade strength safety factor coefficients
- •Questions for self-check
- •4.1. Loads affecting discs
- •The design scheme and assumptions made at disc strength calculations
- •Fig.4.1. Design scheme of the disc
- •4.3. Design ratings
- •4.4. Disc thermal condition
- •4.5. The disc stressed state equation. Boundary conditions
- •4.5.1. An equilibrium equation
- •4.5.2. Equation of deformations generality
- •4.5.3. Determination of stresses in rotating, unevenly heated elastic disc with an arbitrary profile
- •Fig. 4.2. Elementary disc forms
- •Fig. 4.3. Discs of arbitrary profiles
- •4.5.4. The procedure of the arbitrary profile disc stresses calculation
- •4.6. Disc durability criteria and safety factor coefficients
- •4.6.1. Selection of the stressed state criteria
- •4.6.2. Disc safety factor coefficients
- •Integrating an equilibrium equation, we find
- •4.7. Features of strength calculation of centrifugal compressor and radial-inflow turbine discs
- •The weight of the carrier disc for a chosen ring makes
- •Fig. 4.5. Design scheme and character of the radial and circumferential stresses change along radius of two-sided impeller of centrifugal compressor
- •4.8. Peculiarities of stresses calculation in drum-and-disc designs
- •Fig. 4.6. Design scheme of a drum-and-disc rotor
- •From here
- •Questions for self-check
- •Chapter 5. Static strength of gas turbine engine shafts
- •Loads acting on shafts
- •Design schemes and stressed state of shafts. Safety factor coefficient estimation
- •In an axial direction the shaft tensile (compressive) stresses are equal to
- •The shaft static strength is estimated by a safety factor coefficient value
- •Questions for self-check
- •Chapter 6. Dynamic strength of gas turbine engine blades
- •6.1. Vibrations of blades and forces causing vibrations
- •6.2. Kinds and forms of blade normal modes
- •Fig. 6.3. Flexural vibration modes of rotor blades
- •Fig. 6.4. For rotor blade normal mode frequency definition
- •6.3. Normal modes of blades with a stationary cross-section area
- •6.4. Normal modes of blades with a variable cross-section area
- •6.5. Influence of blade attachment effort to the disc
- •6.6. Influence of centrifugal forces on blade vibration frequency
- •F ig. 6.7. Determination of blade dynamic normal mode frequency
- •Influence of variable temperature
- •6.8. Forces damping blade vibrations
- •6.9. Resonant modes of the blade vibrations. The frequency diagram
- •F ig. 6.8. Example of turbine rotor wheel frequency diagram
- •6.10. Torsional and composite blade vibrations
- •6.11. Elimination of blade vibrational breakages
- •6.12. Concept of blades self-oscillations
- •Versus vibration amplitude
- •Questions for self-check
- •Chapter 7. Dynamic strength of gas turbine engine discs
- •General information
- •Forms of disc normal modes
- •Wave linear speed equals
- •Disc normal mode frequency
- •The compressor and turbine rotor wheel vibration calculation
- •Factors influencing the disc normal mode frequency
- •Disc forced undulations
- •The ways to eliminate dangerous resonance oscillations of rotor wheels
- •Questions for self-check
- •Chapter 8. Critical rotational speeds of gas turbine engine rotor
- •8.8. Measures taken to reduce intensity of rotor oscillation connected with critical rotational speeds.
- •Concept of critical rotational speeds of gas turbine engine rotor
- •Critical rotational speed of the two-support weightless shaft with disc
- •Fig. 8.8. Value of shaft static sag for different rotor schemes
- •Fig. 8.9. To the problem of a rotated rotor stability in a subcritical area
- •Connection of rotor critical rotational speed with its
- •Concept of two-support rotor critical rotational speeds of higher order
- •Critical rotational speed of the two-support ponderable shaft without disc
- •8.6. Critical rotational speeds of the ponderable shaft with several discs
- •8.6.1. Method of decomposition into elementary systems
- •8.7. Operational factors affecting critical rotational speeds of gas turbine engine rotor
- •Fig. 8.11. Taking into account supports elasticity influence on rotor critical speeds
- •Fig. 8.12. Static elastic anisotropy of a casing
- •Determination of critical rotational speeds taking into account
- •Influence of gyroscopic moment
- •Table 8.1
- •Values of the influence coefficients
- •8.7.2. Reduction of a real flexural system to equivalent computational
- •Example of rotor critical speed calculation
- •The rotor operational rotational speed margin is equal to:
- •The rotational speed margin at an idle is equal to:
- •8.8. Measures taken to reduce intensity of rotor oscillation connected with critical rotational speeds
- •Questions for self-check
- •8.7. What is dependence of rotor critical rotational speed on its cross-sectional oscillation frequency?
- •Of gas turbine engine shell designs
- •9.1. Shell strength calculation
- •Fig .9.1. Design scheme of a shell
- •9.2. Stability of cylindrical and conical shells
- •9.3. Vibrations of cylindrical shells
- •Questions for self-check
- •Chapter 10. Control of gas turbine engine
- •Vibration state
- •10.2. Control of gas turbine engine vibrations
- •10.3. The ways to lower the vibration level of gas turbine engines
- •10.3.1. The procedures of vibration level lowering at stage of designing
- •10.3.2. The procedures of the vibration level lowering at production stage
- •Fig. 10.3. Scheme of the rotor static balancing
- •Fig. 10.4. Scheme of the rotor dynamic balancing
- •Will be compensated by centrifugal force of balanced elements weights
- •10.3.3. The procedures of the vibration level lowering at maintenance stage
- •Questions for self-check
- •Сhapter 11. Gas turbine engine rotor supports
- •11.1. Brief data about gas turbine engine rotor supports
- •Fig. 11.3. Scheme of gte rotor support
- •11.2. Calculation of support bearings
- •Fig. 11.9. Ball bearing:
- •For roller bearings we use the formula
- •11.2.2. Estimation of the bearing safe life
- •11.2.3. Check of the bearing high-speed
- •11.2.4. Check of the bearing static load-bearing capacity
- •11.2.5. Definition of the necessary oil circulation through the bearing
- •Questions for self-check
Fig. 1.8. Principal scheme of a tpfe with a coaxial propfan
Main stages of gas turbine engines creation
The GTE designing, as well as any technical object designing, consists of a number of successive steps, regulated by state standard. Aircraft developer gives technical requirements (TR) to engine designer. The technical requirements are based on aircraft technical specifications, technical requirements to aircraft, and preliminary general design development of aircraft and engine.
Technical requirements cover the following:
- main designation;
- main technical characteristics;
- major specifications and quality parameters;
- technical economic and special requirements, associated with specificity of the engine application.
Technical requirements are the main normative document at all stages of engine designing and operational development after they have been worked over, agreed and approved.
Preliminary work at engine type selection includes the analysis of various design concepts, finding out their attributes and shortcomings with regard to set requirements, draft calculations and engine characteristics.
One of modern new engine design techniques is the principle of unified (basis) gas generator to be used in different GTEs. Gas generator (high pressure compressor - combustion chamber - high pressure turbine) is the most composite and important TFE unit. The design and specifications of a fan and low pressure turbine being varied within a wide range, a "family" of engines with different designation can be created with one and the same gas generator being used. At this the development expenses will be reduced considerably. For instance, the “General electric” corporation within 15 years has designed 36 different modifications of engines, using the unified gas generator GE1.
The major condition for successful creation of modern engines is that the designers should rely on technological advances to obtain the basic characteristics of engine, details and units (high-pressure fans, smokeless combustion chambers, cooled turbine blades, etc.).
The process of engine designing has the following stages:
- technical proposal (TP) – the whole complex of documents, containing technical, technical and economic grounds for a new engine creation on the basis of TR analysis, preliminary calculations and design developments;
- draft (D) – complete development of engine design with all component units and parts, more detailed calculations; optimization of design versions, making experimental models; consideration and approval of the draft;
- detail design (DD) – the whole complex of design documents, that represent ultimate engineering solutions, which are the initial data for documentation working out;
- preparation of documentation – the final step in designing, which is made in view of particular production technology and tests of engine and all its units. It includes all drafts, calculations and techniques, technical specifications for manufacturing and testing, semi-assembly and assembly communication schemes, assembly drafts, etc. For configuration improvement and ultimate version of communications a full-scale engine model is made. It must be coordinated with an experimental aircraft model.
Each stage of designing process is considered completed after it has been approved and agreed upon, which takes time. Taking into account that the time factor is decisive in engine construction aviation GTE designers practice the system of parallel-consecutive working schedules. This approach enables designers to work at the project more efficiently at early stages of the project development.
At stages of the draft and technical projects development design office staff (designers, technologists, metallurgists and other experts) are involved as well as trade associations and representatives of the customer. They evaluate the level of the engine main parameters and the possibility to reach them, engine reliability, taking into consideration design safety factors, the level of technological effectiveness and labouriousness of manufacturing, maintenance and repair of details and units, verifiability and diagnosing level, material marks used, etc.
Considerable attention is paid to creation of the GTE automatic control system. Specialized design office works on it. The cost of automatic control system development together with system of the engine technical condition estimation, constitutes around 30...40 % of the total cost of GTE development.
There exist a number of stages in between designing accomplishment and engine introduction in a serial production:
- making experimental engines for experimental development;
- testing engines to confirm basic required parameters and characteristics (with necessary design modifications);
- conducting continuous stand tests in order to verify engine strength and reliability;
- conducting special tests to improve and verify engine conformity to given technical requirements;
- flight tests in flying laboratory and special high-altitude stands;
- flight tests in research aircraft;
- administration state testing and introduction in a serial production.
Experimental development plans stipulate that each engine type be put to the whole complex of tests, with the tests mentioned above being performed in a parallel-consecutive order. This will reduce labour and time expenses, the number of experimental engines which makes several dozens of engines.
Parallel-consecutive order in performing design and development operations becomes still more advisable if we take into account the fact that the process of construction of modern engine with prospective parameters takes, on average, twice as long as the process of an equipped airframe desining. According to data received from abroad the construction of a new gas turbine engine takes from 12 to 14 years.
The engine is improved even after it has been put in a serial production. The purpose is to increase engine reliability, improve industrial and operational effectiveness, reduce labouriousness of production and operation, raise the efficiency of diagnostics and failure warning system.
Since the aeroengine design is becoming still more complex, the process of modern aviation GTE design requires that various experts seeking optimum decisions be actively involved.
Gas dynamic and thermal calculations, their implementation in particular designs which are calculated for strength and dynamics, optimization of constructive and technological solutions are impossible without computer-assisted design systems (CADS) being used, which reduce dramatically designing terms, improve the quality of design, allow to release designers from doing routine work giving space to their creative activity.