LINFLOW 1.4 1

Ventilation Fan Aeroelastic Analysis

Rotating Fan Stability Analysis.

(Courtesy of FläktWoods AB, Sweden)

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Ventilation Fan Modeling in LINFLOW

Rotating Fan Stability Analysis.

Twin blade fan model:Rotating at 987 rpmInner radius 0.68 mOuter radius 1.02 m

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Steady Flow

Absolute Velocity Contours.

Steady Flow Analysis of Rotating Fan

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Structural model included fan blades + hub.

Stability analysis was performed using the 8-10 first structural modes with the lowest natural frequencies.

Structural Dynamic Analysis Rotating Fan

Egenmod nummer Frekvens(Hz )

1 126.02 332.43 382.74 438.55 554.36 608.97 736.18 804.29 849.310 891.3

Tabell 1b

Eigenmode table

Structural model used

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Ventilation Fan Aeroelastic Stability Analysis

Aeroelastic Eigenfrequency Diagram Aeroelastic Damping Diagram

One mode showed increasing damping requirements with increasing load, Which?

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LINFLOW predicted an unstable 3.rd mode with a frequency of 382.6 Hz

Measurements at full load later show that a maximum amplitude of vibration existed at 389 Hz

Ventilation Fan Stability Analysis Evaluation

Unstable Mode Shape

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Measurements at full load show that a maximum amplitude of vibration existed at 389 Hz

Ventilation Fan Experimental Response Evaluation

Givare 1

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300 350 400 450 500

f(Hz)

2

1

8

32

1

Measured frequency response diagram.

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Ventilation Fan Unstable Mode Animation

(Click on Picture for Animation)

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Aeroelastic improvements of the fan design

New Improved Ventilation Fan Geometry

Damping requirements for all aeroelastic modesnow drop with increasing loading

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Measurements at full load on the aeroelasticly improved design show more then one order of magnitude lower stress levels on the fan surface.

New Ventilation Fan, Experimental Evaluation

Givare 1:1

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350 400 450 500

f(Hz)

Skovelvinkel 40° Skovelvinkel 35° Multiplar

Measured frequency response diagram.(Return)