Presentation on theme: "LINFLOW 1.41 Ventilation Fan Aeroelastic Analysis n Rotating Fan Stability Analysis. (Courtesy of FläktWoods AB, Sweden)"— Presentation transcript:
LINFLOW 1.41 Ventilation Fan Aeroelastic Analysis n Rotating Fan Stability Analysis. (Courtesy of FläktWoods AB, Sweden)
LINFLOW 1.42 Ventilation Fan Modeling in LINFLOW n Rotating Fan Stability Analysis. Twin blade fan model: Rotating at 987 rpm Inner radius 0.68 m Outer radius 1.02 m
LINFLOW 1.43 Steady Flow Absolute Velocity Contours. Steady Flow Analysis of Rotating Fan
LINFLOW 1.44 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 Eigenmode table Structural model used
LINFLOW 1.45 Ventilation Fan Aeroelastic Stability Analysis Aeroelastic Eigenfrequency DiagramAeroelastic Damping Diagram One mode showed increasing damping requirements with increasing load, Which?
LINFLOW 1.46 LINFLOW predicted an unstable 3.rd mode with a frequency of 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
LINFLOW 1.47 Measurements at full load show that a maximum amplitude of vibration existed at 389 Hz Ventilation Fan Experimental Response Evaluation Measured frequency response diagram.
LINFLOW 1.48 Ventilation Fan Unstable Mode Animation (Click on Picture for Animation)
LINFLOW 1.49 Aeroelastic Instability Alleviation n Can aeroelastic instabilities be eliminated or is it possible to raise the critical velocity? Yes,… … eliminate the source of elastic, inertial, and/or aerodynamic coupling. n How? u Mass balance-- add or redistributed mass to move the c.g. forward. u Modify the vibration characteristics F Increase spread between frequencies F Avoid frequency rations of one or integer multiples F Increase structural damping n Eliminate sources of fluid-dynamic forcing such as vortex shedding or turbulence from wakes etc.
LINFLOW Aeroelastic improvements of the fan design New Improved Ventilation Fan Geometry Damping requirements for all aeroelastic modes now drop with increasing loading
LINFLOW 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 Measured frequency response diagram. (Return)