Numerical Investigation of the Influence of Different Work Distributions on the Performance of Axial Fans for Automotive Cooling Applications

Abstract

In this work the influence of different radial work distributions on the performance of low pressure axial fans for automotive cooling purposes was investigated. The general standard solution in the design of axial fans is to assume constant work distribution (free vortex design). This also leads to a constant meridional flow velocity and thus makes the calculations for the design rather simple. To fulfill the constant work assumption, however, a high swirl component of the absolute outlet flow velocity results near the hub. Assuming the incoming airflow to be swirl-free, this means that the flow near the hub must be strongly deflected, leading to a very high blade load in this area and to very long chords. Thus, the assumption of constant radial work distribution leads to a high risk of flow separation near the hub, especially for low pressure cooling fans, where a small hub to shroud diameter ratio is needed in order to achieve higher flow rates. Furthermore, in fan applications, often the total-to-static pressure and total-to-static efficiency are the relevant design parameters, and not the total-to-total pressure and the total-to-total efficiency. In order to address these issues, linear and parabolic non-constant work distributions were investigated. These distributions were parametrized and for each work distribution a series of designs was created with the airfoil theory method. These designs were computed with the commercial Navier-Stokes-Solver STAR CCM+ and the results were analyzed in detail. As an application example a series of fans for a Formula Student racing cars cooling applications was developed. With this method, it was possible to achieve smaller hub to shroud diameter ratios, higher flow rates and better total-to-static efficiencies. The result was a new series of fans with improved cooling properties for automotive applications. These new fans, the design method and the results are presented in detail in this work.