Optimal Fan Design with 3D Inverse Design

The direct approach for designing a new impeller requires a lot of geometrical parameters. In addition, the correlation between geometrical parameters and aerodynamics is unknown in most cases. Therefore, a lot of CFD calculations or measurements have to be done until the best configuration is reached.

Searching for new tools to make the design process faster and more efficient, an extensive benchmark of available design tools was carried out at ebm-papst. TURBOdesign1 shaped out to be the most suitable tool for developing new fan blades, promising gain of time and a better understanding of the aerodynamics.

With TURBOdesign1, only a few geometrical parameters are needed. The main input is the blade loading, which directly controls the aerodynamic flow field. In particular, TURBOdesign1’s prediction results are very accurate as well as controlling the potential flow field. Figure 2 shows the comparison of the shroud pressure distribution, predicted by TURBOdesign1 and verified with CFD, for a backward curved radial impeller with a diameter of 450 mm. In order to have a fair comparison, CFD analyses were carried out with a simplified meridional channel (see Fig. 1), which is identical to the one used in the design with TURBOdesign1 (no gap between stationary and rotating parts).

Even when considering the actual meridional channel in CFD analyses, as the one reported in Fig. 3, the TURBOdesign1 prediction of the potential flow field is in good agreement with CFD results, as shown in Fig. 4.

The direct control of the potential flow field allows designers to control all the main sources of losses, like the secondary flows and the tip clearance flow, that affect axial and centrifugal fans.

Hence many different designs can be analysed and evaluated without time-consuming CFD calculation. Additionally, the results of a new design can give useful indications as to which parameters are important for the aerodynamics and if the desired pressure rise can be realised. Through easy and fast variation of input parameters, an optimal configuration can be found within minutes.

Conclusion

TURBOdesign1 can be a valuable tool in designing fans. It’s geometrical parameters are reasonable in realising the usual design specifications, with blade loading being an important parameter for aerodynamic and aeroacoustic optimisation.