Toward the CFD Simulation of Sirocco Fans: from Selecting a Turburlence Model to the Role of Celle Shapes

E3 - Flow Characteristic of Centrifugal Fans

Unstructured grid generators are becoming more popular among engineers, due to the significant amount of time that can be saved by using them. They provide a great flexibility in the treatment of any kind of geometry with minimum user interaction. Selecting an appropriate cell shape from the list of available cell shapes supported by the CFD tool, can have a major influence on the accuracy of the solution and reliability of the results. This should be done considering the physics of the flow, available computational recourses and the complexity of the geometry. Applying a proper mesh configuration to CFD simulations leads to better numerical stability and faster convergence of the solution.
In addition to mesh configurations, selecting a proper turbulence model is another factor which improves the accuracy of a simulation. Turbulence models should be selected according to the computational effort, required accuracy, physics of the flow, etc.

In this study performance curves of Radial fans with forward curved blades, which are also called Sirocco fans are obtained by performing CFD simulations. Sirocco fans are capable of delivering considerably more air volume and also produce higher static pressure than many other centrifugal fan types of the same size and speed(but at the expense of lower efficiencies). Sirocco fans are often used in small furnaces, electronic equipment, ventilation, and air conditioning (HVAC) applications. The lower efficiencies of sirocco fans are due to the inevitable formation of recirculation zones which form between the blade channels of the fan.

In this study, simulation results are presented in two parts, the first includes results of the simulations performed using different turbulence models. These simulations are carried out by using three of the most popular turbulence models i.e. two-equation Realizable k-ε model, two-equation SST k-ω and the one-equation model of Spalart-Allmaras.

Second part includes results of the simulations performed by applying different mesh configurations. Simulations are performed by using four mesh configurations which consist of three unstructured grids that are generated using the same mesh properties by means of different cell shapes i.e. polyhedral cells, trimmed cells and the combination of polyhedral cells (for Rotor) and trimmed cells (for Stator), and a structured grid which is generated by means of ANSYS ICEM mesher.