Experimental and Numerical Investigation of a Gearless One-motor Contra-Rotating Fan

B2 - Theoretical & Numerical Methods for Axial Fans

Compared to single rotor fans with discharge guide vanes, contra-rotating fans reduce the swirl in the wake flow as well as achieve a higher power densities. In practice, this approach is already being used to expand the application range of axial fans due to the higher total pressure rise and increased efficiency.
Conventional contra-rotating fans utilize one motor for each rotor or a gear for power transmission. This installation is more complicated, expensive and requires more maintenance compared to single rotor fans. In order to overcome these disadvantages, a new gearless one-motor concept was developed for compact fans at the Institute of Air Handling and Refrigeration in Dresden, Germany. Its diameter is 200mm with an design point of 650 m³/h at 2100 rpm. Due to the innovative design, the torque is equally distributed between both rotors improving the flow field inside the fan.
Different setups were experimentally investigated. Firstly, the performance map of a single stage fan was measured with and without a discharge guide vane with 10 and 19 blades, respectively. The additional guide vanes improve the performance of the single rotor fan. Secondly, the newly developed contra-rotating fan was analysed. The results show an improved efficiency and performance compared to a single rotor fan. Finally, stereo particle image velocimetry was utilized to visualize the flow field and detect optimization potential.
In a second step, numerical computations are conducted to furthermore analyse the flow field of the single-rotor and contra-rotating fan. The incompressible flow is simulated using the open-source CFD library OpenFOAM. Steady-state simulations are performed using the multiple reference frame approach for modelling the movement of the rotors. The SST k-omega turbulence model is utilized.
The simulation of the performance map and the velocity profiles show a good agreement with the experimental data.