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Turbomachinery Design Considerations

Turbomachinery Design Considerations. EGR 4347 Analysis and Design of Propulsion Systems. Euler Pump Equation. Compressor Axial Schematic. Compressor Centrifugal Schematic. Compressor Typical Velocity Diagram. Compressor Repeating Row Nomenclature. Airfoil Pressure and Velocity.

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Turbomachinery Design Considerations

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  1. Turbomachinery Design Considerations EGR 4347 Analysis and Design of Propulsion Systems

  2. Euler Pump Equation

  3. Compressor Axial Schematic

  4. Compressor Centrifugal Schematic

  5. Compressor Typical Velocity Diagram

  6. Compressor Repeating Row Nomenclature

  7. Airfoil Pressure and Velocity

  8. Important Parameters • Compressor Efficiency, c • Stage Efficiency, s • Polytropic Efficiency, ec • Stage Pressure Ratio, s • Overall Pressure Ratio, c

  9. Degree of Reaction • Desirable value around 0.5

  10. Diffusion Factor • Quantifies the correlation between total pressure loss and deceleration (diffusion) on the upper (suction) surface of blade (rotor and stator) •  is the solidity – the ratio of airfoil chord to spacing

  11. Diffusion Factor Data

  12. Hub, Mean, and Tip Velocity Diagrams

  13. Stall and Surge

  14. Parameters Affecting Turbine Blade Design Vibration Environment Number of Blades Tip Shroud Airfoil Shape Inlet Temperature Trailing-Edge Thickness Blade Cooling Allowable Stress Levels (AN2) (N = Speed, RPM) Material Service Life Requirements

  15. Turbine Prelim Design Focuses on Defining a ‘Flowpath’ that Meets Customer Requirements AN2 wrh a,b Wc Clearance Customer Req’ts/Desires Performance Mission Cost & Risk FN, SFC Req’ts Aero Technology Life Req’ts Mech. & Cooling Technologies Performance Cycle Design Material Selections Component Temp to other areas Combustor Design Turbine Aero Design Turbine Mech Design Manufacturing No No Meet Requirements Yes Preliminary Design = “Frozen” Turbine Flowpath

  16. Turbine Mechanical Detailed Design • Detailed Design Accomplishes Two Functions: • Verify Assumptions/Choices Made in Preliminary Design • Provide Detailed Geometry Required to Achieve Preliminary Design Goals • Detail Mechanical Design Disciplines: • Materials Selection - satisfy life/performance goals • Secondary Flow Analysis - define/control nonflowpath air (e.g. cooling) • Heat Transfer - component temperature definition • Stress Analysis - component stresses • Vibration Analysis - design to avoid natural frequencies • Life Analysis - define component life for all failure modes

  17. Turbine Nomenclature

  18. 50% Reaction Turbine

  19. 0% Reaction or Impulse Turbine

  20. Hub, Mean and Tip Velocity Diagrams

  21. “ABSOLUTE” FLOW ANGLES “RELATIVE” BLADE ANGLES Velocity Triangles Relating a’s and b’s

  22. TURBINE ANALYSIS – Velocity Triangles

  23. u2 V3 v2 v3 V2 u3 inlet, i exit, e TURBINE ANALYSIS • Euler Turbine Equation: convention: v3 = -ve also, ri = re= r

  24. TURBINE ANALYSIS • Turbine Efficiency: • Adiabatic (Isentropic) • Polytropic • Stage Loading Coefficient, y: • Typical values: 1.3 - 2.2

  25. TURBINE ANALYSIS • Flow Coefficient, F: Typical values 0.5 - 1.1 • Degree of Reaction, °R: • °Rt = 0 Impulse turbine • Reaction turbine

  26. TURBINE ANALYSIS • Pressure Loss Coefficient, ft: • Velocity Ratio, VR: Typical values: 0.5 - 0.6 Tip Leakage Cooling Loss Profile Loss Endwall Loss

  27. Turbine Mechanical Design • AN2: Rotor Exit Annulus Area x [Max Physical Speed]2 • Units: in2 x RPM2 x 1010, typical values: 0.5<AN2<10 x1010 • Typical Limits: • Cooled Blade < 5 x 1010 • Advanced Technology < 6.5 x 1010 • Uncooled Solid Blade < 10 x 1010 • LPT < 7 x 1010 • Use max physical speed; not design point or TO speed • Blade Airfoil Stress is Primarily Driven by AN2 • Blade Pull Load Driven by AN2

  28. Turbine Mechanical Design – Hub and Tip Speed Limits • rhw2: Hub radius x 2p/60 x Max Physical RPM • Units: ft/s • Typical Values: • HPT - 1000 ft/s < rhw2< 1500 ft/s • LPT - 500 ft/s < rhw2< 1000 ft/s • Use max physical RPM; not design point or TO speed • Disk Stress is Driven Primarily by rhw2 • Disk and Blade Attachment Stresses are a function of rhw2 and AN2

  29. Structures - Rotational Stress (Centrifugal Stress) - Bending Stress due to the lift of “airfoils” - Buffet/Vibrational Stress - Flutter due to resonant response - Torsion from shaft torque - Thermal Stress due to temperature gradients - FOD - Erosion, Corrosion, and Creep

  30. Structures

  31. Structures

  32. T+DT T T0 0 rH r r q rH Disk Structures - Stress Calculations • - Rotational Stress (Centrifugal Stress) • -- Same as for compressor, sc, sblade • -Disk Thermal Stress, st • -- assume T = T(r) = T0 + DT(r/rH) • -- a - coef of linear thermal expansion • -- E - Modulus of Elasticity radial stress tangential stress

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