Patterns in change and balancing of aerodynamic imbalance of the low­pressure axial fan impeller

Abstract

We have studied patterns in the change and balancing of aerodynamic imbalance of the impeller for the axial fan of type VO-06-300 (Ukraine). We have found the aerodynamic imbalance of the impeller caused by mounting one blade: – at a different angle of attack; – with a violation in the step uniformity; – not perpendicularly to the longitudinal axis of the impeller; – with all three of the above-mentioned errors present at once. We have estimated a change in the aerodynamic imbalance due to change in air density. We estimated the influence of air temperature, altitude above sea level, atmospheric pressure, on air density and aerodynamic imbalance. It was established that a different angle of attack and a violation of the perpendicularity give rise to the dynamic imbalance in which the moment component is an order of magnitude larger than the static component. A violation of the step uniformity gives rise only to the static component, which is in the plane of the impeller. Among the errors considered, the most undesirable one relates to mounting a blade at a different angle of attack. At such an error, aerodynamic imbalance is 6‒8 times larger than that due to other errors. A ±4-degree change in the angle of attack of a single blade in the impeller can degrade the accuracy of balancing of the impeller to the accuracy class G 6.3 at a frequency of 1,500 rpm, or G 16 ‒ at 3,000 rpm. It was established that the ordinary and aerodynamic imbalances can be balanced at the same time. It is appropriate to carry out dynamic balancing in two correction planes. It is possible to conduct balancing by rotor mass correction or using passive auto-balancers. A specific example is used to demonstrate the procedure for taking into consideration the aerodynamic imbalance in differential equations of motion of the axial fan. In accordance with the procedure, the aerodynamic imbalance components are added to the respective components of the ordinary imbalance. The results obtained are applicable when designing and manufacturing low-pressure axial fans. Employing them would improve vibration characteristics of the specified fans.