Aiming at the contradiction between low air pressure and large air volume and low noise in the performance of air conditioner fans, this study selected an axial flow fan prototype with excellent performance for air conditioners as a comparative research model for curved swept design. The basic structure of the prototype is: impeller outer diameter 409mm, impeller diameter 120mm, impeller ratio 0.29, number of blades 4, flow rate 2220m3/h, static pressure 20Pa, speed 880r/min. The design of the new fan is based on the premise of ensuring the flow rate, focusing on improving the internal flow distribution of the fan to reduce noise.

        The design of the new fan is based on previous fluid dynamics research and existing quasi-3D design methods, using leading edge sweep technology and CFD/CAD coupling. CAD estimation is performed on the structural characteristics of a typical prototype wind wheel, and full 3D CFD calculations are performed using the commercial software FLUENT to examine its external and internal flow characteristics, which are then compared and analyzed with experimental results. Conventional methods are used to make a preliminary quasi-3D impeller design, and CFD calculations are performed to examine its external and internal flow characteristics. The CAD/CFD results of the prototype fan and the new fan are compared and analyzed, and the relevant parameters of the initial design are adjusted to achieve a better aerodynamic layout plan. CFD is used to predict the performance of the fan after adjustment, and the relevant parameters are further adjusted based on the calculation results to further optimize the fan.

       In addition, the design also needs to consider parameters such as blade chord length, blade installation angle, blade camber angle, airfoil mid-arc line, etc. These parameters should be optimized and reasonably matched with each other to improve the aerodynamic-acoustic performance of the fan.

Taking all the above factors into consideration, the basic structure of the new fan is designed: fan outer diameter 408 mm, hub diameter 100 mm, hub ratio 0.245, number of blades 4, blade tip/blade root chord length 276/80 mm, forward bend angle 44°, and forward sweep angle 20°.

       In the same outdoor unit, numerical simulations were performed on the prototype fan and the new fan respectively. The actual machine was appropriately simplified during the calculation, without considering the influence of the heat exchanger, outlet grille, motor and its bracket, but taking side air intake into account.

       The finite volume method is used to discretize the control equations and solve the three-dimensional steady flow field of the entire outdoor unit in a separated implicit manner. The Spalart-Alm arcs turbulence model is used for the calculation, the second-order upwind difference format is used for the convection term, and the pressure-degree coupling is solved using the standard SIM PLE algorithm.

Due to the complexity of the fan system, the entire computational domain uses unstructured grids with a total grid number of 110 x 104. The area where the impeller is located is defined as the rotating area and has a larger number of grids. Pressure boundary conditions are used at the inlet and outlet, with atmospheric conditions at the inlet and different back pressures at the outlet. When the residual value of each calculation is less than 1 x 10-3, the calculation is considered to have converged.