Body force models are a valuable tool for inexpensively numerically simulating the performance of turbomachinery such as  
axial fans. The approach involves replacing the blades with body forces in the form of momentum and (for compressible flow) energy source terms. Such models do not resolve the detailed flow over the blades but instead capture a “smeared out” version of the blades’ effect on the flow. This reduces grid requirements and, more importantly, allows the use of steady computations even in cases of non-uniform flow. The body force model used in this paper has been widely used in aircraft engine applications. The implementation of the approach for low speed, low solidity (few blades) turbomachines, such as automotive cooling fans, enables predictions of cooling flows and component temperatures predictions from numerical  simulations without calibrated fan curves; only the blade geometry is needed. Automotive cooling fans tend to have a relatively small number of blades, typically less than 10, which is approximately 50% of the blade counts for modern jet engine fans. The effect this has on the body force model predictions is unknown and the objective of this paper is to quantify  
how varying blade count affects the accuracy of the predictions for both uniform and non-uniform inflow. We present the results of computations carried out in OpenFOAM using both body force and bladed approaches in low-speed incompressible flow.  
The key findings indicate that significant reduction of blade metal blockage effects combined with the effects of spanwise flow redistribution drives the body force model to predict more accurate values of the fan work coefficient as the blade count decreases, and that the reduction in the number of blades is found to have negligible impacts on upstream influence and distortion transfer in non-uniform inflow until extremely low blade counts (such as 2) are applied, at which point the upstream flow becomes more uniform and the distortion is transferred almost unaltered through the fan.


The Effect of Blade Count on Body Force Model Performance for Axial Fans

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

Turbo Expo - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.