© Frank Kameier - Fluid Mechanics and Acoustics 1 Frank Kameier Professor for Fluid Mechanics and Acoustics Unsteady Aerodynamics in Turbomachines Rotating Stall and Surge Rotating Instabilities and Blade Vibrations (Flow-induced Vibrations) The „Demonstrator“ of FH Düsseldorf

© Frank Kameier - Fluid Mechanics and Acoustics 2 Operating Map (Compressor)– non dimensional Rotating Instabilities Rotating Stall Surge Design Conditions

© Frank Kameier - Fluid Mechanics and Acoustics 3 Flow Separation in a Turbomachine(Compressor) NGV Dresden   „Abrupt Stall“

© Frank Kameier - Fluid Mechanics and Acoustics 4 Surge Conditions High Pressure Compressor A pressure wave with an amplitude of several bar propagates from rear to front stages. Damage of the rotor blades after app surge cycles.  

© Frank Kameier - Fluid Mechanics and Acoustics 5 Instrumentation – Wall Pressure Transducers - Kulite XT190  4 mm Piezo-resisitive (DC up to 30 kHz )

© Frank Kameier - Fluid Mechanics and Acoustics 6 Surge Test Nhrt=60% Expansion Wall pressureTemperature

© Frank Kameier - Fluid Mechanics and Acoustics 7 Wall Pressure Fluctuations at Surge Conditions

© Frank Kameier - Fluid Mechanics and Acoustics 8 Wall Pressure Fluctuations at Bang-Test-Conditions axial shot = plane wave

© Frank Kameier - Fluid Mechanics and Acoustics 9 Wall Pressure Fluctuations at Bang-Test-Conditions lateral shot = non plane wave

© Frank Kameier - Fluid Mechanics and Acoustics 10 Surge Analysis in a 10-Stage Compressor

© Frank Kameier - Fluid Mechanics and Acoustics 11 Rotating Instabilities – a Periodic Vortex Shedding? Flow around a cylinder R.Feynman, Lectures on Physics, 1974

© Frank Kameier - Fluid Mechanics and Acoustics 12 Kármán Vortex Separation Causes Mechanical Damage Ferrybridge, England 1965 Ref.: Sahlmen, Niemann

© Frank Kameier - Fluid Mechanics and Acoustics 13 Kármán Vortex Separation Causes “Stall Flutter”

© Frank Kameier - Fluid Mechanics and Acoustics 14 Rotating Instabilities – a Wall Shear Stress Fluctuation? Schlichting, Boundary Layer Theory

© Frank Kameier - Fluid Mechanics and Acoustics 15 Rotating Instabilities and Blade Vibrations Wall pressure fluctuations - fixed frame of reference - Blade vibrations - rotating frame of reference - BAUMGARTNER, KAMEIER, HOURMOUZIADIS, ISABE Conference, Melbourne, 1995 Restricted speed range

© Frank Kameier - Fluid Mechanics and Acoustics 16 Rotating Instabilities and Blade Vibrations Wall pressure fluctuations - fixed frame of reference - Blade vibrations - rotating frame of reference -

© Frank Kameier - Fluid Mechanics and Acoustics 17 Tip Clearance Effect of an Axial Flow Machine

© Frank Kameier - Fluid Mechanics and Acoustics 18 High pressure compressor U/min Low speed fan 1400 U/min

© Frank Kameier - Fluid Mechanics and Acoustics 19 High Pressure Compressor – Speed Variation f[Hz] t[s] p[Pa]

© Frank Kameier - Fluid Mechanics and Acoustics 20 Acoustic Resonances – Aero Engine Occurence Speed of sound is the speed of propagation Helmholtz-Resonator Standing waves and orifice resonance Self-induced acoustical resonances - „Parker Modes“ – Orgen-pipe resonances bzw. Sharp peak! [Hz]

© Frank Kameier - Fluid Mechanics and Acoustics 21 “Acoustic Resonance” Downstream of a Flat Plate in Flow Quelle: Parker, Aeroacoustics, International Journal of Fluid Dynamics,

© Frank Kameier - Fluid Mechanics and Acoustics 22 Wall Pressure Fluctuations Upstream Rotor 1(HPC)   Operating conditions on secondary characteristics Rotating stall

© Frank Kameier - Fluid Mechanics and Acoustics 23 Wall Pressure Fluctuations Upstream Rotor 1(HPC)   Operating conditions close to design Transonic flow in the blade tip region

© Frank Kameier - Fluid Mechanics and Acoustics 24 Rotor 1 Redesign - Wall Pressure Fluctuations   Operating conditions close to surge margin Redesign

© Frank Kameier - Fluid Mechanics and Acoustics 25 Circumferential Distribution of Rotating Instabilities Wall Pressure Fluctuations Power spectrum Coherence Phase spectrum

© Frank Kameier - Fluid Mechanics and Acoustics 26 Rotating Stall as a Special Case of Rotating Instabilities „Rotating Stall“

© Frank Kameier - Fluid Mechanics and Acoustics 27 Rotating Stall in a Compressor Blade Row

© Frank Kameier - Fluid Mechanics and Acoustics 28 Negative Frequencies and Rotating Stall

© Frank Kameier - Fluid Mechanics and Acoustics 29 Rotating Stall – Part Span Stall Turbotech II - Teilvorhaben Nr Fixed frame Rotor frame

© Frank Kameier - Fluid Mechanics and Acoustics 30 Historical Review: „Instabilities“ in the Atmosphere of the Earth (Chen, Haupt, Rautenberg, Uni Hannover, 1987) A circumferential propagating Kármán vortex street: Rossby-wave

© Frank Kameier - Fluid Mechanics and Acoustics 31 Rotating Stall in a Centrifugal Impeller Quelle: Bohl, Strömungsmaschinen, 1994

© Frank Kameier - Fluid Mechanics and Acoustics 32 Sound Generation by Rotating Stall in Centrifugal Turbomachines Inlet DuctImpeller Blade Rotating Instability (Mongeau, Pennsylvania State University, 1991)

© Frank Kameier - Fluid Mechanics and Acoustics 33 Rotating Instability Waves in a Ducted Axial Fan (Krane, Bent, Quinlan, AT&T Bell Laboratories, 1995)

© Frank Kameier - Fluid Mechanics and Acoustics 34 Rotating Instabilities in a Steam Turbine (Low Pressure Stage) Power spectrum Coherence along circumference vgl.: Truckenmüller, Gerschütz, Stetter, Hosenfeld, Uni Stuttgart, ImechE, London 99

© Frank Kameier - Fluid Mechanics and Acoustics 35 Rotating Instabilities - Periodical Unsteady Flow Field Within a Rotor Blade Row of an Axial Compressor (TU Dresden) vgl.: Mailach, Vogler, Lehmann, TU Dresden, ASME Montreal 2007

© Frank Kameier - Fluid Mechanics and Acoustics 36 Rotating Stall Rotating Instabilities separated flow randomised behaviour turbulent frequencies are not related to the number of rotor blades separated flow discrete behaviour periodical frequencies are related to the number of rotor blades

© Frank Kameier - Fluid Mechanics and Acoustics 37 Correlation of Vibration and Pressure Fluctuations – Measurements on the Demonstrator of FH Düsseldorf (Co-op Rolls-Royce Germany)

© Frank Kameier - Fluid Mechanics and Acoustics 38 Unsteady Instrumentation – Fixed Frame of Reference Transducers - 16 ¼‘‘ Microfones Microtech MK301. -Accelerometer B&K Polytec Laservibrometer Transducer positions -84 circumferential positions,  = 4.285°. -6 positions in the rotor wake region,  = 60°.

© Frank Kameier - Fluid Mechanics and Acoustics 39 Unsteady Instrumentation – Rotating Frame of Reference Blades with transducers Transducer - 4 Pressure transducers Kulite LQ-47 und LQ125 - Strain Gages HBM - Rotating 8-chanel amplifier unit DLR Berlin, 4 x Kulites, 4x Strain Gage -10 – chanel slip ring unit

© Frank Kameier - Fluid Mechanics and Acoustics 40 Unsteady Instrumentation – Rotating Frame of Reference Strain Gage Pressure Transducers LQ-47, LQ125 Transducer - 4 Pressure transducers Kulite LQ-47 und LQ125 - Strain Gages HBM - Rotating 8-chanel amplifier unit DLR Berlin, 4 x Kulites, 4x Strain Gage -10 – chanel slip ring unit

© Frank Kameier - Fluid Mechanics and Acoustics 41 Unsteady Instrumentation – Rotating Frame of Reference 8-Channel amplifier unit (rotating) 10-Channel Slip-ring Transducer - 4 Pressure transducers Kulite LQ-47 und LQ125 - Strain Gages HBM - Rotating 8-chanel amplifier unit DLR Berlin, 4 x Kulites, 4x Strain Gage -10 – chanel slip ring unit

© Frank Kameier - Fluid Mechanics and Acoustics 42 Continuous Throttle Procedure n=1000min -1 – Wall Pressure Excitation of Modes  =   Fixed Frame of Reference, = 60°, 1000min -1,  f = 1Hz Rotating Frame of Reference, = 60°, 1000min -1,  f = 1Hz

© Frank Kameier - Fluid Mechanics and Acoustics 43 Continuous Throttle Procedure n=1000min -1 - Rotating Frame of Reference (Strain Gauge) - Soft Blade f eigen ~ 69Hz   Stiff Blade f eigen ~ 97Hz Excitation of Modes  =

© Frank Kameier - Fluid Mechanics and Acoustics 44 Continuous Throttle Procedure n=1000min -1 - Increased Blade Loading - Fixed Frame of Reference – Excitation of Modes  = 5, 6, 6.5 und  Rotating Stall

© Frank Kameier - Fluid Mechanics and Acoustics 45 Statistical Analysis of Rotating Instability and Rotating Stall Rotating Stall Gauß Distribution Rayleigh Distribution RI-Frequenzen Umgebungsrauschen Histogram of Rotating Stall amplitudesHistogram of Rotating Instability amplitudes

© Frank Kameier - Fluid Mechanics and Acoustics 46 Rotating Stall and Rotating Instabilities „primary“ - Characteristics Stall region Rotating Instabilities (Schematical Sketch) Rotating Stall (Schematical Sketch)

© Frank Kameier - Fluid Mechanics and Acoustics 47 Flow Field with RI Flow visualization - Single stage compressor along throttling procedure Tip Clearance Flow Quelle: Kameier Small GapLarge Gap  Rotorblade Starting Hypothesis Small GapLarge Gap Small GapLarge Gap No secondary flow region, no separated boundary layer Secondary flow region Point of separation

© Frank Kameier - Fluid Mechanics and Acoustics 48 Low Flow Rate Separated Flow Region High Flow Rate

© Frank Kameier - Fluid Mechanics and Acoustics 49 High Flow Rate Low Flow Rate Separated Flow Region

© Frank Kameier - Fluid Mechanics and Acoustics 50 Tip Clearance s*= 0%, Low Flow Rate Tip Clearance Variation Tip Clearance s*= 2%, Low Flow Rate

© Frank Kameier - Fluid Mechanics and Acoustics 51 Summary Stufe 1 RS RS+RI RI

© Frank Kameier - Fluid Mechanics and Acoustics 52 Rotating Instabilities  Rotating instabilities occur in radial and axial flow machines.  RI is explained as a pulsating separated flow region which is rotating relative to the rotor in rotor direction (slip condition).  It is impossible to predict a rotating instability.  A numerical model is not known yet.

© Frank Kameier - Fluid Mechanics and Acoustics 53 Fluid Mechanics and Acoustics at FH Düsseldorf Institute of Sound and Vibration Engineering (in the course of formation) CAE of centrifugal flow machines (funded by BMBF) Low noise design (Outflow Valve Boeing 787) Flow induced vibrations (funded by BMW AG) Steady state CFD for localising unsteady mechanisms (funded by BMW AG) Combustor resonances (funded by Weishaupt GmbH) Noise reduction of roots compressors (funded by Lufttechnik KG) Optimisation of vacuum cleaner (Aeroacoustics) (funded by Miele) Current Research and Development