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The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise
of a Forward-Curved Blade Radial Fan
Manoochehr Darvish Bastian Tietjen Stefan Frank
Contents
2 The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
Flow inside radial fans with forward-curved blades
Simulation setup (CFD/CAA)
Turbulence model & mesh configurations
Experimental measurements
Noise generation in forward-curved blades fans
The importance of the cut-off geometry
Methods to reduce the tonal noise of forward-curved
blades fans
3
Radial fans with forward-curved (FC) blades have some
unavoidable flow-separation zones even at the Best Efficiency
Point (BEP)
active
inactive
Inactive zone in the rotor can grow up to one third of the
rotor width
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
STAR-CCM+ Simulation
STAR-CCM+ Version 7.04
Simulations start from converged steady solutions
RANS (SST k-omega), DES (SST k-omega), LES
Non-reflecting inlet/outlet boundaries (Free-Stream)
Segregated solver
Compressible flow
2nd order temporal discretization
Rotational speed:1000 rpm
Number of blades:38
Time Step becomes gradually smaller : 1°,0.75°,0.5°,0.25°
rotation of the fan-wheel
4
BPF = 16.667 * 38 ~ 633 Hz
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
STAR-CCM+ CFD/CAA Simulation
• Monitoring the maximum pressure in the fan discharge
• Ffowcs Williams-Hawkings (FW-H) receiver is placed near the
outlet
• The whole geometry is assigned to FW-H surface (noise source)
5 The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
6
Different Turbulence Models (Methods) Different Flow Features
URANS
DES
LES Iso-surface v=20 m/s
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
7
16.5M Cells 7 days/rev
26.5M Cells 10 days/rev
12.5M Cells 5 days/rev
Detached Eddy Simulation
102 M Cells 35 days/rev
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
12.5 million cells
Accurate prediction of the tonal and broadband noise (up to 1200 Hz)
Computational power: 64 core server with 256 GB RAM
8
Experimental Noise Measurement According to DIN/ISO 5136
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
9
F (Hz)
Tonal Noise: Interaction between the impeller blades and the cut-off
Broadband Noise: Vortex shedding at the trailing edges & turbulent flow acting on solid surfaces
Blade Passing Frequency (BPF)
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
The Source of Noise in FC Fans
10
Static Efficiency= 35%
Static Efficiency= 46%
Tongueless Design vs. Optimum Design
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
11
Optimum Design Tongueless Design
Tongueless design: No tonal noise component but louder broadband noise
BPF: 633 Hz
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
12 The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
How to Reduce the Tonal Noise of FC Fans
Unsteady flow leaving the impeller
Strong pressure fluctuations at the
cut-off
Tonal noise generation
Reducing the Tonal Noise :
Impeller Making the velocity profile more uniform
Number of blades
blade outlet angle
Volute
Local noise cancellation at the cut-off
Employing phase-shift tongues
Increasing impeller-tongue clearance
Negative effect on the fan performance
13
0°
90°
270°
180°
The velocity profiles become more uniform by increasing the number of blades
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
14
30 Blades
38 Blades
48 Blades
Different Blade Outlet Angles
160° 165° 170°
Different Number of Blades
38 Blades
38 Blades
38 Blades
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
15 The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
Changing the Blade Outlet Angle
Increasing the outlet angle : Better performance especially in the overload range Slight reduction of the tonal noise
16 The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
Changing the Number of Blades
Increasing the number of blades: Better performance especially in the overload range Effective reduction of the tonal noise
17
Pressure side
Suction side
30 Blades (BPF=500 Hz)
38 Blades (BPF=633 Hz)
48 Blades (BPF=800 Hz)
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
18
Designing Phase-Shift Volute Tongues
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
Stepped tongue geometries with 0.5 and 1 Blade-to-Blade (BtB) height difference
0.5 BtB
1 BtB
633 Hz (BPF)
19
Designing Phase-Shift Volute Tongues
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
0.5 BtB
1 BtB
Pressure monitors: Phase-shift only in the 0.5 BtB model
20
Tonal noise at BPF (633 Hz) Reference 0.5 BtB 1 BtB
Experiment (dB) 62 57 62
Pressure-Monitor (dB) 64 62 64
FW-H (dB) 59 55 59
The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
Designing Phase-Shift Volute Tongues
Conclusions
Tonal noise of the radial fans with forward-curved blades can be reduced by making some geometrical modifications.
The geometrical changes which uniformize the velocity profile of the flow leaving the blades have the potential to reduce the tonal noise.
Increasing the number of blades not only reduced the tonal noise component but also improved the performance of the fan.
Increasing the blade outlet angle can also reduce the tonal noise, yet not as effective as increasing the number of blades.
CFD simulations helped to design new volute tongue geometries which generate phase-shift effects and locally cancel the noise at the cut-off.
Efficiency of the fan should always remain in focus, since even a simple change in the design of the fan can affect its performance.
21 The Role of Computational Fluid Dynamic and Aeroacoustic Simulations in Reducing the Noise of a Forward-Curved Blade Radial Fan
Thank you for your attention!