Effect of the Uneven Circumferential Blade Space on the Performance of Small Axial Flow Fan

Effects of the uneven circumferential blade space on static characteristics and aerodynamic noise of a small axial flow fan are studied in this work. The blade angle modulation is adopted to design a series of unequally spaced fans, which have different maximum of modulation angular displacement. The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model, while the unsteady flow is computed with large eddy simulation. According to theoretical analysis, a fan with a maximum of modulation angular displacement of 6 is regarded as the optimal unequally spaced fan. The experiment of static characteristic is carried out in a standard wind tunnel and the aerodynamic noise of both fans is tested in a semi-anechoic room. Then, performances of the optimal unequally spaced fan are compared with those of the prototype fan. The results show that there is reasonable agreement between the simulation results and the experimental data. It is found that the discrete noise of the optimal unequally spaced fan is lower than that of the prototype fan at the near field monitoring point. This can be explained that the total pressure fluctuation of the optimal unequally spaced fan is much more regular than that of the prototype fan.