1 / 43

MAE 5350: Gas Turbines

MAE 5350: Gas Turbines. Advanced Concepts Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk. AEROENGINE CORE POWER EVOLUTION: DEPENDENCE ON TURBINE ENTRY TEMPERATURE [Meece/Koff]. TURBINE COOLING TRENDS.

csweet
Download Presentation

MAE 5350: Gas Turbines

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MAE 5350: Gas Turbines Advanced Concepts Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk

  2. AEROENGINE CORE POWER EVOLUTION: DEPENDENCE ON TURBINE ENTRY TEMPERATURE [Meece/Koff]

  3. TURBINE COOLING TRENDS • Thrust and performance increases monotonically with turbine inlet temperature, qt • Isp and hthermal also increase • Because of associated increase in pc • STRONG INCENTIVE TO INCREASE qt • Turbine efficiency decreases • Blade materials: oxidation-resistant, high s, such as Nickel and Cobalt based alloys • Introduction of directionally-solidified and single-crystal blade materials Increase limited by metallurgical progress Most current advancement due to air-cooling

  4. WHERE DOES COOLING AIR COME FROM? Turbine blades cooled with compressor discharge air Other components (burner, liners, disks, etc.) also cooled with compressor air

  5. OVERALL COMMENTS • Cooling air drawn from compressor • Must be at higher pressure than that part of flow path to be cooled • Blades are cooled by combination of internal and external cooling • Internal cooling: Convection driven • External cooling: Film Cooling

  6. COOLING SYSTEMS

  7. COOLING STRATEGIES: INTERNAL COOLING • Cooling air is pumped through inside of blades • Air is pumped in at root and makes multiple passes before exiting at root • Material is cooled by forced convection on inside surface and by conduction through blade • Different regions of blades can have different cooling profiles • Large surface area on inside • Many designs employ roughened internal microfin structure

  8. COOLING STRATEGIES: FILM COOLING

  9. FILM COOLING BEHAVIOR

  10. FILM COOLING OPTIONS

  11. FILM COOLING OPTIONS

  12. EXAMPLE OF FILM-COOLING DATA x/D • Cooling Effectiveness, h (often called adiabatic film effectiveness) • Tr = Adiabatic recover temperature = the temperature wall would reach if adiabatic (no heat transfer) in the absence of film cooling • Trf = recovery temperature in the presence of film cooling

  13. TREMENDOUS AMOUNT OF DATA AVAILABLE B ≡ (rU)jet / (rU)∞ ~ 0.5 B ≡ (rU)jet / (rU)∞ ~ 1.0

  14. 2780 1800 2492 1640 2204 1480 1916 1320 1628 1160 1340 1000 1052 840 764 680 476 520 188 360 200 -100 °F K COOLING JET BEHAVIOR: CFD Attached Jet: B ≡ (rU)jet / (rU)∞ ~ 0.5 A-A: x/D = 10 A-A Lifted Jet: B ≡ (rU)jet / (rU)∞ ~ 2.0 A-A x/D = 10

  15. COOLING STRATEGIES: TRANSPIRATION COOLING • Wire cloth or mesh is used for exterior of blade and air is leaked uniformly through it • Consists of a plurality of wires made of metal, ceramic or other materials, and arranged with their longitudinal axes generally and not necessarily precisely, parallel to the blade axis, either with or without a stiffener insert • Ample porosity is provided for transportation cooling • Cools surface and provides a protective layer

  16. HOW TO DESIGN COOLED BLADES One of the most difficult areas of gas turbine design • Estimate wall heat flux (qw) over blade surface for specified wall temperature (Tw) • Find thermal stresses in the skin • Find the reduction in qw required to limit stresses to acceptable values → find h required of film cooling • Find the arrangement of cooling holes and cooling air flow for film cooling to provide the required effectiveness • Find the internal cooling airflow to absorb residual qw

  17. ENGINE MATERIALS • Different materials used in Rolls-Royce jet engine • Blue: titanium is ideal for strength and density, but not at high temperatures • Red: nickel-based superalloys • Orange: steel used for the static parts of the compressor • Green: Composite

  18. PW4084: COLOR SCAN SOON!

  19. ADDITIONAL ISSUES AND BLADE TESTING • Other Issues • High Cycle Fatigue • Materials • Manufacturing • Containment of Blade • Disk Rupture • Sealing • Tip and Hub Losses • Turbine Cooling Bleed • Inspection • Replacement Parts ($) ‘Blade-Out’ Simulation

  20. BLADE MATERIALS AND GROWTH • Although blade cooling can reduce temperatures, heat transfer limitations still exist and ht↓ • Conventionally cast blades (inexpensive) • Myriad of crystals which gives multidirectional mechanical properties • Failure usually at boundary between crystals, long term creep • Directionally solidified blades (cost ↑) • Blade is comprised of many long or columnar crystals • Blade made out of a Ni-base super alloy • Directionally-solidified, resulting in a columnar grain structure which mitigates grain-boundary induced creep • Single crystal blades (cost ↑ ↑ ↑) • No crystal boundaries • Multidirectional mechanical properties • Blade is directionally-solidified to permit only one crystal to grow into blade

  21. BLADE AND VANE MANUFACTURING (FLACK) • Two-piece die made that is very accurate “negative” of eventual blade shape (used thousands of times). • If blade is hollow, ceramic core in exact shape of internal passages placed in die. Ceramic core is “negative” of passages. • Die is filled with hot paraffin-based wax (liquid), and wax is allowed to cool and harden. Waxes are chosen so that they do no shrink upon cooling. • Die is separated and wax piece is removed. Wax is now an exact replica of eventual metal blade. If eventual blade is hollow, ceramic core is still in wax replica. • Wax blade is coated (by dipping, spraying, or both) with a slurry and then stucco with multi-layers. A silica, alumina, or other ceramic “flour”, or a combination of these is used to create stucco shell. • Wax inside of stucco shell is melted and escapes through exit holes. If blade is to be hollow, ceramic core remains accurately in place in stucco shell. • Stucco shell, which is heat resistant, is filled with blade material and blade material is allowed to cool. • Stucco shell is removed from blade by air or sand blasting. • If hollow core is present, ceramic core is removed by immersion in a caustic solution that dissolves internal ceramic core. • Finishing or trimming accomplished by removing any metal used for holing blade in place. • Blades are inspected by X-ray and fluorescing surface die for internal and surface defects. If minor defects are found, they are repaired. If major imperfections are found, blade is discarded. • Some blades are coated with a very thin film of a poor heat conductor (usually ceramic) • Any surface holes for film cooling are “drilled” using precise, electrochemical, electrodischarge, waterjet, or laser machining • Some machining may be needed on root (fir tree) for placement on wheel or drum. After this expensive and long multi-step process, blades are ready for installation.

  22. HIGH FUEL TO AIR PROBLEM / CHALLENGE • To increase specific thrust, future engines will increase overall fuel-air ratios • JSF affected Flow Direction JSF Compressor Combustor Turbine F119

  23. PHENOMENOLOGICAL OVERVIEW PW229 SURFACE HEAT FLUX IMPACT EMISSIONS INTO TURBINE EXHAUST MIGRATION

  24. F119-100 1st ROTOR

  25. F119-100 1st ROTOR

  26. BOAS: BLADE OUTER AIR SEAL

  27. BLADE OUTER AIR SEAL POST EVENT

  28. DETAIL

  29. TURBINE ROTOR BLADE FAILURE (ROLLS-ROYCE)

  30. RESEARCH QUESTIONS • What is impact to turbine surfaces due to secondary reactions? • What is change in surface heat flux due to a local reaction over a range of operating conditions • What is influence of blowing ratio, B? • What is influence of the total fuel content, E? • What is influence of flow and chemical time scales, Da = tflow/tchem? • Etc… • What if you knew answers? • How do you use this information? • How to incorporate into a design system framework?

  31. EXPERIMENTAL INVESTIGATION Fuel rich air flow Air-Side Injection Heat Flux Gauges Nitrogen-Side Injection

  32. EFFECT OF LOCAL REACTIONB = 1.0, Da = 13, CO = 65,000 ppm (Moderate Energy Content) Downstream Upstream 25% augmentation over inert side Cooled side injection agrees to within 10% of literature values and correlation

  33. 2780 1800 2492 1640 2204 1480 1916 1320 1628 1160 1340 1000 1052 840 764 680 476 520 188 360 200 -100 °F K CFD STUDY: B = 0.5 (ATTACHED JET) TOTAL TEMPERATURE CONTOURS — Tflame = 1840 K Da < 1 Maximum Temperature = 1200 K, 0 % of potential (cold flow) A-A A-A: x/D = 10 Da > 1 Maximum Temperature = 1715 K, 80 % of potential Note maximum wall heat release at z/D = +/- 0.5 x/D = 10

  34. 2780 1800 2492 1640 2204 1480 1916 1320 1628 1160 1340 1000 1052 840 764 680 476 520 188 360 200 -100 °F K CFD STUDY: B = 2.0 (LIFTED JET) TOTAL TEMPERATURE CONTOURS — Tflame = 1840 K Da < 1 Maximum Temperature = 1200 K, 0 % of potential (cold flow) x/D = 10 Da > 1 Maximum Temperature = 1683 K, 75 % of potential x/D = 10 Note maximum wall heat release at z/D = 0.0

  35. 2500 2100 1700 1300 900 K IN-LINE AND STAGGERED HOLE GEOMETRIES Numerical studies extended to engine conditions B = 1.0, Da = 0.3, H* = 0.54, Qs ~ 0% B = 1.0, Da = 0.3, H* = 0.54, Qs ~ 70% Staggered hole (z/D~3) at low B (0.5-1.0) provides ‘good’ surface protection: burning is kept off-surface, h > 0.15

  36. ENGINE BEARINGS AND ARRANGEMENTS • Engines are unusual among engineering structures in that such a large fraction of their total mass is rotating at high speed • This large rotating mass must be supported on bearings to maintain close clearances between blade tips and stationary casing • On order of 1 mm on a rotor of 1 m diameter, or 1 part in 103 • All existing engines use ball and roller bearings to support the rotating assemblies

  37. BEARING TYPES • Each rotating spool is supported by one ball bearing • Positions spool axially • Absorbs radial loads • Each rotating spool also supported by one or more roller bearings • Accepts radial loads • Allows axial movements to accommodate thermal expansion and structural deformations • Also provides location for squeeze films for damping • Increases speed at which rotor can operate • Decreases vibrations

  38. ADDITIONAL EXAMPLES: THERMAL STRESSES • Beam constrained by two unmovable walls • Heat added at some location • When material gets hotter, volume expands (thermal expansion) • But no room for body to move since constrained by both walls • Compressive stress is induced in material to produce a strain that cancels thermal expansion • If body is locally cooled → thermal contraction → induced tensile stress

  39. EXAMPLE OF THERMAL STRESSES

  40. ZOOM IN TO SEE DETAILS Bearing locations Mechanism to vary compressor stator angles

  41. ROTATING SHAFT DYNAMICS: SIMPLE MODELS Simplified spring mass damper model Very large amplitudes possible if near critical frequencies

  42. DISK DESIGN

More Related