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Numerical Investigation of Reynolds
Number and Pitch Ratio Effect on
Lock-in Ability
of an Aeroacoustic Field in Ducted
Fl...
Aeroacoustic Resonance of Bluff Bodies in Ducted Flows
 Noise intensification
 It can occur when a Gas Flow in a duct/ca...
Aeroacoustic Resonance Behaviour of Tube Array
10 15 20 25 30
0
500
1000
1500
2000
V
(m/s)
Pa(Pa)
10 15 20 25 30
0
100
20...
Conditions for Resonance
(Hall, Ziada, Weaver data -2003)
Lock-in map (EXPERIMENTAL DATA)
Conditionsforresonance
Amplitude...
Research Motivations and Objectives
• Mechanism of lock in is not yet clear
• Effect of turbulence increasing and
variatio...
CFD Simulation of Aeroacoustic Resonance
ACOUSTICS
IS
“ COMPRESSIBLE”
INCOMPRESSIBLE
FLOW
(uRANS, SST) += OSCILLATING VELO...
Application
Two cylinders in tandem
Four cylinders in square
In line multiple cylinder array
Vortexsheddingfrequency
Flow ...
Pressure,PascalsPressure,Pascals
PreCoincidence 𝑓𝑎 /𝑓𝑣 =1.2
Coincidence 𝑓𝑎 /𝑓𝑣 =0.85
Two Cylinder Resonance- Reynolds numb...
LOCK-IN and Velocity contours
% V inlet
Normalized velocity
WITHOUT EXCITATION
% V inlet
Normalized velocity
case NOT LOCK...
EXPERIMENTAL ACOUSTIC POWER
Acoustic Power
NUMERICAL ACOUSTIC POWER
(Finnegan, Meskell and Ziada data-2010)
PreCoincidence...
Four Cylinder Resonance - Summary of Results
Coincidence 𝑓𝑎 /𝑓𝑣 =0.85
PICTH 2.5
• Lock in only occurring at
Coincidence an...
Multiple Cylinder Array Resonance - Summary of Results
Coincidence 𝑓𝑎 /𝑓𝑣 =0.85 –Pitch L/D 2.5 PICTH 2.5
• Lock in only oc...
Conclusions
 The cylinder configurations analysed have
shown a different resonance response to
the similar lock in excita...
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Numerical Investigation of the Reynolds Number and Pitch Ratio Effect on the Lock-In Ability of an Aero-Acoustic Field in Ducted flows".

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Numerical Investigation of the Reynolds Number and Pitch Ratio Effect on the Lock-In Ability of an Aero-Acoustic Field in Ducted flows".

  1. 1. Numerical Investigation of Reynolds Number and Pitch Ratio Effect on Lock-in Ability of an Aeroacoustic Field in Ducted Flows Dept. of Mechanical and Manufacturing Engineering Trinity College Dublin Cristina Paduano
  2. 2. Aeroacoustic Resonance of Bluff Bodies in Ducted Flows  Noise intensification  It can occur when a Gas Flow in a duct/cavity exhibits Periodic Vortices Vortex shedding Duct acoustic mode 𝒇 𝒗 𝒇 𝒂 HYDRODYNAMIC Vortex shedding at acoustic frequency 𝒇 𝒗 = 𝒇 𝒂 Tonal noise is emitted Vortexsheddingfrequency LOCK-IN Flow velocity flow 𝒇 𝒂 𝒅𝒖𝒄𝒕 Off resonance Off resonance NOISE SELF-SUSTAINS and ENHANCES
  3. 3. Aeroacoustic Resonance Behaviour of Tube Array 10 15 20 25 30 0 500 1000 1500 2000 V (m/s) Pa(Pa) 10 15 20 25 30 0 100 200 300 400 500 V (m/s) Frequency(Hz) Pressure measurements (heat exchanger) UNPREDICTABLE VELOCITY EXTENTS OF LOCK IN RANGE UNKNOWN Velocity measurements (heat exchanger) 140 dB (images from Finnegan -2011) “Tube array resonance occurs when the energy available in the flow(dynamic head) overcomes the acoustic damping of the system” - (Feenstra et al.- 2006)
  4. 4. Conditions for Resonance (Hall, Ziada, Weaver data -2003) Lock-in map (EXPERIMENTAL DATA) Conditionsforresonance Amplitude of the acoustic wave Frequency ratio This research: Reynolds number and Pitch ratio • To understand aeroacoustic resonance in tube array it is necessary to understand the strength of the sound sources formed around the tubes. • Numerous experimental study for reduced array configuration (single -2- 4 cylinders) used a fixed width test section ( 1 fa) and varied fv.
  5. 5. Research Motivations and Objectives • Mechanism of lock in is not yet clear • Effect of turbulence increasing and variation of the vortices patterns were indicated as possible parameters contributing to resonance of tube array (Fitzpatrick -1980, Ziada-1989). However many experiments focused more on variation of frequency ratio.  Is there a flow characteristic which causes Lock in to occur ?  Does the aeroacoustic resonance of 2 and 4 cylinders configuration represent the aeroacustic resonance of tube array ? Vortexsheddingfrequency Flow velocity 𝒇 𝒂 𝒇 𝒗 =1 Vortices incoherent structure Coherent acoustic sources Vortices incoherent structure LOCK IN FLOW STRUCTURE
  6. 6. CFD Simulation of Aeroacoustic Resonance ACOUSTICS IS “ COMPRESSIBLE” INCOMPRESSIBLE FLOW (uRANS, SST) += OSCILLATING VELOCITY (BOUNDARY CONDITION) Hydrodynamic Analogy (Tan ,Thompson, Hourigan-2003) TRASVERSAL ACOUSTIC WAVE replaced by the Flow OSCILLATION which it causes RESONANCE: 𝑓𝑎 chosen to be in LOCK-IN ratio with 𝑓𝑣 𝑼 𝒂𝒄𝒔=Asin(2 𝑓𝑎t)
  7. 7. Application Two cylinders in tandem Four cylinders in square In line multiple cylinder array Vortexsheddingfrequency Flow velocity 𝒇 𝒂 𝒇 𝒗 =1 Pre-coinc. resonance Coinc. resonance IMPOSED LOCK IN CONDITION FLOWSTRUCTUREVARIATION TURBULENCE EFFECT Mean flow velocity variation applied (i.e. RE variation 10000-36000) VORTICES CONVECTIVE VEL. VARIATION Variation of vortices convective velocity is obtained by varying the pitch ratio L/D 2.5-3. (Configuration analysed – Re and pitch as Finnegan-2011)
  8. 8. Pressure,PascalsPressure,Pascals PreCoincidence 𝑓𝑎 /𝑓𝑣 =1.2 Coincidence 𝑓𝑎 /𝑓𝑣 =0.85 Two Cylinder Resonance- Reynolds number dependency  Lock in only occurring above Re 27000 –Reynolds number dependency
  9. 9. LOCK-IN and Velocity contours % V inlet Normalized velocity WITHOUT EXCITATION % V inlet Normalized velocity case NOT LOCKED IN (Re=10000) Normalized velocity case LOCKED IN (Re=36000) Normalized velocity WITHOUT EXCITATION % V inlet% V inlet
  10. 10. EXPERIMENTAL ACOUSTIC POWER Acoustic Power NUMERICAL ACOUSTIC POWER (Finnegan, Meskell and Ziada data-2010) PreCoincidence 𝑓𝑣 < 𝑓𝑎 Coincidence 𝑓𝑣 > 𝑓𝑎 Sinks (Flow takes energy from acoustics) Sources (Flow puts energy into acoustics) PreCoincidence 𝑓𝑣 < 𝑓𝑎 Coincidence 𝑓𝑣 > 𝑓𝑎
  11. 11. Four Cylinder Resonance - Summary of Results Coincidence 𝑓𝑎 /𝑓𝑣 =0.85 PICTH 2.5 • Lock in only occurring at Coincidence and for all Reynolds numbers PICTH 3 • Lock in only occurring at Coincidence ONLY at the higher Reynolds number Pressure,Pascals Coincidence 𝑅𝑒 36000 (𝑃𝑖𝑐𝑡ℎ 2.5) (Finnegan, Meskell and Ziada data-2010)
  12. 12. Multiple Cylinder Array Resonance - Summary of Results Coincidence 𝑓𝑎 /𝑓𝑣 =0.85 –Pitch L/D 2.5 PICTH 2.5 • Lock in only occurring at Coincidence and for all Reynolds numbers PICTH 3 • Lock in NEVER OCCURRING (Finnegan, Meskell and Ziada data-2010) Coincidence 𝑅𝑒 36000 (𝑃𝑖𝑐𝑡ℎ 2.5)
  13. 13. Conclusions  The cylinder configurations analysed have shown a different resonance response to the similar lock in excitation;  The onset of resonance appeared to be influenced by the Reynolds number (Two cylinders case) and influenced by the variation of the cylinders Pitch ratio (Four cylinders case); The frequency ratio could not be the only parameter instigating acoustic resonance, the flow condition (i.e. Turbulence and Vortices Convective Velocity) should be considered as well. RE Pre-Coinc. Coinc. Two Cylinders (L/D 2.5) 12000 36000 No resonance Resonance No resonance Resonance Four Cylinders (L/D 2.5) 12000 36000 No resonance No resonance Resonance Resonance Four Cylinders (L/D 3) 12000 36000 No resonance No resonance No resonance Resonance Array (L/D 2.5) 12000 36000 No resonance No resonance Resonance Resonance Array (L/D 3) 12000 36000 No resonance No resonance No resonance No resonance

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