PowerPoint Presentation

Propulsion:Axial Flow Compressor & FanAerospace Engineering, International School of Engineering (ISE)Academic year : 2012-2013 (August December, 2012)

Jeerasak Pitakarnnop , Ph.D.Jeerasak.p@chula.ac.thjeerasak@nimt.or.th

Aircraft Propulsion2October 27, 2012IntroductionFirst rotating component that the fluid encounters.Basic function:Impart kinetic energy to the working fluid by means of rotating blades, thenConvert the increase in energy to an increase in total pressure.

The pressure ratio increases, the required fuel flow decreases and the extracted power increasesOctober 27, 2012Aircraft Propulsion3IntroductionDesign of an efficient axial flow fan/compressor is a complex process which often involve success or failure of an engine CFD tools can efficiently be use for complex 3D analysis and design.Addition functions:A small portion of the air is bled to provide some cockpit and electronic environmental control.A small portion is bled to provide pressurized air for inlet anti-icing.Some of the high-pressure cool air is directed to the turbine and used to reduce the temperature of hot turbine blades.October 27, 2012Aircraft Propulsion4GeometryOctober 27, 2012Aircraft Propulsion5

Tip and housing diameter are approximately constantthrough a compressor.Rotor blades: do the work on fluid.Stationary blades: do not input any energy but necessary for guiding the flow.Typical number of stage is from 5 to 20, the total pressure ratio across a single stage is typically from 1.15 to 1.28.

5GeometryOctober 27, 2012Aircraft Propulsion6

DiskInlet & Exit Guide VanesInlet Guide Vanes (IGV): Same function as stator vanes but the design is quite different.They turn the incoming air, which is in the axial direction in a direction of 1st rotor blades incident free.Exit Guide Vanes (EGV)A set of stator vanes after the last stage that readies the flow for entrance to the combustor.Design to add swirl to the flow, which aids in mixing within the combustor. October 27, 2012Aircraft Propulsion7Compressor Stage OperationOctober 27, 2012Aircraft Propulsion8

A stage: a rotor wheel carrying blades+ a stator assembly carrying stationary blades or vanesProper flow direction from IGV or stator of previous stage Conceptual unwrappingof middle sectionConsider the flow at some midspan blade section (between hub and tip).Investigation of stage aerodynamics is usually carried out in a cascade tunnel, an experimental setup where single or multi-stage cascades are tested under simulated flow conditions.3D effects occur in an actual compressor but for study purposes flow in a cascade is considered to be 2D.Absolute velocity V as seen by an external observer standing next to the engine.Circumferential velocity U depending on rotational speed (rpm) and radial position.Relative velocity Vrel as seen by an observer sitting on the rotating blade and moving with it.2D Simulation in CFD

October 27, 2012Aircraft Propulsion9Velocity Polygon or TrianglesOctober 27, 2012Aircraft Propulsion10

Inlet Guide VanesOctober 27, 2012Aircraft Propulsion11

The inlet flow to IGV is typically aligned with the axis of the engineThe axial flow velocity relative to the engine flame (absolute velocity) at the IGV inlet is c0.Exit blade angle relative to the axis of the engine..Exit flow angle relative to the axis of the engine..The absolute flow velocity (velocity in the non rotating flame) at the IGV exit is c1.1st Stage RotorOctober 27, 2012Aircraft Propulsion12

Resulting velocity in a rotating frame w1. has a flow angle 1.Abs. vel. c1 has component in tangential direction cu1In axial direction ca1Rel. vel. w1 has component in tangential direction wu1In axial direction wa1Relate the velocities in the stationary ref. frame to those in rotating frame

If 1 = 1 incidence angle is 0. Difficult to happen in off-design conditions The difference at tailing edge 2 and 2 is called the deviation. 1st Stage StatorOctober 27, 2012Aircraft Propulsion13

The relative flow velocity (velocity in the rotating flame) at the rotor exit is w1.The absolute flow velocity (velocity in the stationary flame) at the stator exit is c2.The absolute flow velocity (velocity in the stationary flame) at the stator inlet is c1.2nd Stage RotorOctober 27, 2012Aircraft Propulsion14

2nd Stage StatorOctober 27, 2012Aircraft Propulsion15

Side View of First StageOctober 27, 2012Aircraft Propulsion16

Blade HeightRadius of the bladeSingle-Stage Energy AnalysisRelate the velocity from polygons to the pressure rise and otherAxial Flow Compressor component TrendsOctober 27, 2012Aircraft Propulsion17

Total Pressure RatioPower Input to the ShaftOctober 27, 2012Aircraft Propulsion18Total Pressure Ratio of the Stage

The equations is derived for a single stage (rotor and stator) using 2D planar mean line c.v. approach.Midway between hub and tipControl Volume definition for compressor stagePercent ReactionA relation that approximates the relative loading of the rotor and stator based on the enthalpy rise:October 27, 2012Aircraft Propulsion19

Incompressible FlowPower Input to the ShaftOctober 27, 2012Aircraft Propulsion20Total Pressure Rise of the Stage

For comparison, the pressure rise and percent reaction of a turbomachine with an incompressible fluid can be found from the following equations:Percent Reaction

Relationships of Velocity Polygons to Percent Reaction and Pressure RatioOctober 27, 2012Aircraft Propulsion21

Relationships of Velocity Polygons to Percent Reaction and Pressure RatioOctober 27, 2012Aircraft Propulsion22

Limit on Stage Pressure RatioThe rotor is moving, the relative velocity must be used:October 27, 2012Aircraft Propulsion23

For the stator, which is stationary the relative velocity must be used:

1 and 2 refer to the stage inlet and midstage properties.Limit on Stage Pressure RatioRotorOctober 27, 2012Aircraft Propulsion24Stator

Ex1 : Velocity Polygon A stage approximating the size one of the last stages (rotor and stator) of a high-pressure compressor is to be analyzed. It rotates at 8000 rpm and compresses 127 kg s-1 of air. The inlet pressure and temperature are 1.875 MPa and 727.6 K, respectively. The average radius of the blades is 335.28 mm and the inlet blade height is 31.496 mm. The absolute inlet flow angle to the rotor is the same as the stator exit flow angle 15, and the rotor flow turning angle is 25. The stage has been designed so that the blade height varies and the axial velocity remains constant through it. The efficiency of stage is 90%. The value of cp and are 1.08311 kJ kg-1 K-1 and 1.361, respectively, which are based on the resulting value of T2 or average static temperature of the stage. The following details are to be found: blade heights at the rotor and stator exits, the static and total pressures at the rotor and stator exits, the required power for the stage, and the percent reaction for the stage.October 27, 2012Aircraft Propulsion25