Turbomachinery. Overview

Transcription

1 Turbomachinery Overview Turbomachinery -1 Definition Widely used in aerospace propulsion propellers, fans, s, turbines, pumps, turbopumps, Also energy/power conversion gas turbines, wind turbines, water turbines, steam turbines, Turbomachinery definition devices that transfer energy through expansion/compression of a continuously moving fluid by blade rows (rotating blades) so not piston-based compression/expansion devices turbomachinery.com nrel.com geaviation.com Turbomachinery -2 1

2 Configurations Typically characterized by flow direction versus axis of rotation axial flow primarily parallel to axis radial entering or exiting flow perpendicular to axis mixed in-between the two extremes from J. Skorpik Turbomachinery -3 Axial (Flow) Compressors and Turbines Shaft Stator/Stator Vanes Inlet Guide Vanes Rotor/Rotor blades turbine Nozzle Casing Rotor Stage=Rotor/Stator Pair Turbomachinery -4 2

3 Axial Compressors and Turbines Disk (blades attached to it) Blisk if blades integrated into disk (Turbine) Rotor Blade braytonenergy.net Spool - and turbine rotors on common shaft Turbomachinery -5 Axial Compressors and Turbines Spool and turbine rotors on common shaft GE F404 LP spool 3 rotors (3 stages) Turbomachinery -6 turbine 1 rotor (1 stage) 3

4 Axial Compressors and Turbines most engines have at least two spools e.g., concentric shafts 3 stage LP 7 stage HP GE F404 Pr c ~26 Pr stage ~1.4 Turbomachinery -7 Centrifugal (Radial) Compressor Modified nomenclature rotor/impeller PW100 LP single piece Turbomachinery -8 4

5 Mixed (Axial-Centrifugal) Compressor Some engines use both axial and centrifugal components Turbomachinery -9 Euler Turbomachinery Equations How to analyze the performance and design turbomachinery? Start by developing conservation equations First define appropriate control volume for rotating machinery Turbomachinery -10 5

6 Euler Turbomachinery Equations Mass d 0 dv c nˆ da dt CV 0 0 m m 2 m m m 2 Angular Momentum torque CM law d mrc dt d rc dv rc c nˆ da dt CV CS Turbomachinery CS steady 0 for steady okay if time avg. over high freq. fluctuations that result from blades going by rc rc ˆ c nda mrc rc either some spatial avg. or rc 2 CS 1 must be uniform ( vortex free ) for prelim. design, typically use the mean radius location (between inner and outer radii) 1 Turbomachinery -12 Euler Turbomachinery Equations So m rc rc 2 1 what about power? Power/Energy from mechanics W m rc rc W m u c from thermodynamics u c W m h o h 2 o1 steady, adiabatic, uniform h 2 1 r = blade speed u h u c u c for equations as written, W 0 for /pump, W 0 for turbine 6

7 Other Important Definitions Reaction (Degree of Reaction) hrotor R h stage energy change across rotor balance torque, p gradient between rotor/stator Flowfields (axial machines) real machines have 3-d flows simpler, consider 2-d flows (different planes) Throughflow Field (r-z plane) no variations disk replaces blades energy change across stage p ~ p rotor stage r z Turbomachinery -13 Other Important Definitions Cascade Field (-z plane) no r variations like unwrapping blade to look at array of airfoil sections our focus Secondary Field (r- plane) no z variations low velocity in boundary layers along blades/walls pressure gradients produce secondary (rotational) flows leads to reduced performance (efficiency loss) blade r blade z Turbomachinery -14 7