Ansys Fan of Simulation

 

Fan of Simulation

Voith Turbo reduces costs while developing quiet fans by  simulating a complete railcar cooling system.

 

By Bernd Horlacher and Steffen K?mmerer, Development Engineers, Voith Turbo, Crailsheim, Germany

 

At certain operating conditions, the highest noise levels in rail vehicles come not from the engine but the cooling units, especially the fans. Increasingly stricter exhaust  regulations and growing output requirements call for higher and higher cooling performances, which could lead to greater noise pollution. 

 

Voith Turbo in Germany developed a plan to address these competing parameters in the rail industry.Voith Turbo is a leading company specializing in power transmission used in industry as well as on the road, rails and water. Equipment from Voith Turbo Cooling systems, a div-ision of Voith Turbo, operates safely and reliably in railcars and locomo-tives all over the world, including high-speed trains (diesel–hydraulic, diesel–electric and electric). These cooling systems, used to cool diesel engines, transmissions, transformers, inverters, throttles and drive motors, require an induced air mass flow that is created using high-capacity fans. 

 

One disadvantage of classic fan design is that excessive noise is  emitted at rotational speeds of  3,500 rpm and blade tip velocities up to 360 km/hr. To reduce the sound level, engineers from Voith Turbo Cooling systems and researchers at the University of siegen in Germany developed Voith silentVent? tech-nology. Applying this technology to railcars and locomotives alike was a  challenge: The cooling systems in railcars are installed on top of the roof or under the floor and, therefore, are quite compact when compared to  the cooling systems for locomotives. 

 

 

The inlet to the fan is often blocked, so the flow entering the blade  passages are often highly distorted. This can reduce efficiency and increase noise generated by the fan.

 

 The cooling system consists of four heat exchangers and three axial fans in which the fan inlets are  separated by metal partitions and blocked by tubes/pipes and holding plates. The scenario studied was  a railcar that had come to rest in a  railway station after traveling at high speed. Its fans are still rotating at  full speed to dissipate the heat, but, because there is no natural wind, the warm air can be drawn back into the heat exchangers. This recirculation flow could degrade the operation  of the entire cooling system. To accu-rately simulate these conditions,  a large domain outside the cooling system and railcar was taken into account. With nearly 50 million  elements, the mesh of the cooling  system was necessarily very large. The grid generated needed to strike a balance between attention to detail and available resources to ensure that the simulation time was reasonable, but parts such as the fan were finely discretized to predict areas of separation, critical in obtaining accurate solutions.

 

For this model, the heat exchangers were idealized and defined as a porous medium. Using the full porous model available in Ansys CFX software, which is based on Darcy's Law, the model of the heat exchanger was calibrated by adjusting the loss coefficient to emulate the characteristic curve (loss of pressure versus  volume flow).

 

Visualization of the flow using streamlines did not show any  recirculation flow through the heat exchangers for the cooling system model with either the Voith standard fan or silentVent technology. Each fan showed a clean outflow. By using fluid dynamics technology from Ansys, the engineers were able to determine the volume flow rate of each fan and distribution of flow from the heat exchangers to the fans. The team established fan design data such as torque, rated input, pressure increase and efficiency for the  complete cooling system — infor-mation that is not easy to obtain on a fan test under idealized conditions.The engineers also used the Ansys CFX Turbo noise macro....

 

 

 

Ansys Fan of Simulation.PDF