Fluid Dynamic Design and Optimization of a Double Entry Fan Driven by Tractor Power Take Off for Mist Sprayer Application

A3 - Numerical Optimisation of Centrifugal Fan Performances

Mist sprayers are commonly used in conventional agriculture for the distribution of herbicides, pesticides and fertilizers. For this purpose in particular, truck-mounted mist sprayers are used to spray insecticides to trees, shrubs, and tall grass in rural areas and to road borders and courtyards in urban areas.
The coupling of a fan, used to supply air to a mist sprayer, and a IC engine is problematic since, in this case, for the correct design of the fan it is not possible to define a priori the operating point. In fact, the rotational speed is not fixed as in the case of an electric motor driven fan, but is determined as an equilibrium of the power supplied by the engine and the power absorbed by the fan to recover the pressure drops of the mist sprayer system.

In this paper, the fluid dynamic design of a double entry fan driven by tractor power take off for mist sprayer applications is presented. The design is carried out by means of an integrated 1D/3D numerical procedure based on the use of CFD simulations.

Moreover, an experimental campaign performed to characterize the existent fans is presented. The collected data are elaborated in order to fix a design starting point and to validate the CFD procedure.
The CFD simulations are then used either at the preliminary design stage to choose among competitive one- or two-dimensional geometries and then to test the generated three-dimensional geometries. The results show how the different design choices could impact on the performance parameters and, finally, how the analysis of the various alternatives allows the determination of the overall geometry of a complete and performing centrifugal fan.

Finally, the double entry fan has been prototyped and tested. The test confirmed that the designed fan met the manufacture requests in terms of efficiency, maximum flow rate, head and noise level.