Research On Vibration Of Direct Air-cooling Fan Tray

In direct air-cooling system,The fan support system will be caused a greater fan tray vibration during fan and drive system in operation.which is related to operating frequency of fan system,the stiffness of the fan tray, vibration isolation measures of fan tray. Excessive vibration of fan tray will bring hidden dangers to the safe operation of the plant. In this paper, A systematic study is carried out on vibration performance fan tray in direct air-cooling fan system and on the basis of the direct air-cooling fan power plant in Shanxi Youyu,combining on-site measurement and analysis of finite element numerical simulation method. It is reported that the fan tray vibration is mainly from the blade vortex excitation force, and blade vortex excitation frequency is approximately equal to the basic fan blade rotation frequency multiplied by the number. A method of computing fan blade disturbance force is proposed. The main conclusions are as follows.(1) Main factors causing fan tray disturbance force are:centrifugal force arising by the initial eccentricity as forced vibration excitation force; moment and torque effects generated by aerodynamic lift and resistance to the blades of the fan shaft,which is also called bending-torsion coupling vibration;Vortex excitation effect on fan blades will be generated when fan system running speed is accelerating.the most important factor is Vortex excitation effect generated by the blades of the fan tray.(2) By on-site vibration test and FEA simulation on fan system and fan trays, it is further demonstrated that the source of vibration is mainly from the vibration source vortex excitation effect generated by the fan blades, the frequency of source equals to the fan rotation frequency multiplied by the blades number; Inertia force due to the eccentric rotor of the fan tray is also one of the reasons causing the vibration, which is relatively smaller than vortex excitation effect generated by the fan blades, which is not dominated factors in fan tray design, from design opinion the vibration of the fan tray should not only avoid self-resonant frequency excitation frequency eddy current generated by the fan blades, but also should avoid the rotational frequency of the fan.This is one of the most effective ways to reduce vibration on the fan tray.(3) When five-blades rotate at a frequency of50Hz-55Hz, the fan blade vortex excitation frequency is8.585Hz-9.44Hz, which is close to a first-order vibration frequency in fan tray horizontal or vertical direction.When six-blades rotate at a frequency of4.122Hz-12.462Hz, the fan blade vortex excitation frequency is8.238Hz-11.328Hz, which is close to a first-order vibration frequency in fan tray horizontal or vertical direction there may even cause "category resonance" phenomenon.(4) By motoring dynamic response on vibration resource of fan system the following rules can be followed: vibration source intensity changes significantly varied with the rotation frequency, the basic rule is:slow increasing of vibration source intensity is slow in the range of20Hz-30Hz,when frequency reaches30Hz vibration source intensity correspondingly reaches at maxima; vibration source intensity is relatively stable in the rang of30Hz-45Hz frequency, vibration source intensity changes little; within the range of45Hz-55Hz, the vibration source intensity increases with increasing rotation frequency, when arriving55Hz frequency, intensity reached another Extreme point which is also the maximum value of vibration source intensity to all the fan system under rotating frequency.(5) By on-site vibration test and FEA simulation on fan system and fan trays,we can do this ways to decrease the vibration of fan trays:adds the number of the blades;use lower motor; increase the stiffness of the rail;use prop up rod on the motor plate and so on. It's helpful to the design of fan trays.(6) The fan shaft axial strain peak value of the fan shaft axial spectral response curve in the vicinity of the excitation frequency eddy current.The maximum value of an shaft section moment is not increased with the fan rotating frequency increasing, the peak occurred in some frequency section. Dynamic response and vibration intensity of fan tray changes and on-site measured fan shaft section moment of rotating frequency peak with different change rule is consistent, further verify axial strain of the fan shaft test results is reasonable. According to on-site vibration test and FEA simulation results on and fan trays system, a design approximate calculation formula is proposed on fan shaft disturbing force computing (ie, the total moment of fan shaft section) which can be recommended for direct air-cooling fan tray design.