Study on Design Optimisation of Centrifugal Fan of High Voltage Generator by Numerical Analysis
3.6 Case Studies: Aerodynamics
A generator is a device that converts the mechanical energy provided by an engine, a gas turbine, a steam turbine, etc. to electrical energy. Heat is generated during the energy conversion process and the internal temperature of the generator is increased. If the temperature rise exceeds the specification limit, the deterioration of the insulation is promoted or burned out. A cooling fan is applied for the purpose of suppressing the temperature characteristic of such a generator to within the numerical value in the standard. The cooling fan must maintain a constant temperature by equalizing the amount of heat and the amount of cooling by satisfying the required air flow rate and required static pressure. We have studied the optimal design of cooling fan to satisfy required air flow rate, static pressure and fan efficiency inside the generator. The generator to be developed for the cooling fan is a high-voltage generator of 5MW class maximum. Four kinds of centrifugal fans were designed by design variables according to blade type, blade length, blade angle, and number of blades. The cooling performance by flow rate and static pressure was compared through numerical analysis. For the numerical analysis, ANSYS ICEM-CFD grid generator program was used and about 4 million cubic lattices were generated. A simple algorithm was used to obtain the steady state flow field, and the flow field at 900 rpm was simulated using the moving wall condition on the blade surface and the MRF method for the air rotation field around the fan. The model of the fan duct according to the AMCA standard was modeled and the outlet pressure condition was changed and calculated. In addition, the turbulent flow was predicted and the Standard K-EPSILON turbulence model, one of the turbulence models in Fluent, was used.
Through the numerical analysis, we could analyze the cooling performance of cooling fan design according to the blade variable of Four kind of fans. In order to verify the numerical analysis of four fans, a fan performance device was designed according to the AMCA standard and the cooling performance according to the static pressure of the same RPM was compared. As a result of the verification, similar performance difference tendency was shown, and about 10% flow rate and static pressure were measured lower than the analytical result. In this study, the optimal fan design considering the system resistance is considered as a numerical analysis technique, and a method for reducing the development cost and time is provided.