FEM + CFD simulation: When there's a crash in the filter

Filter systems are often considered unspectacular. But when they are installed at a height of 14 meters, have to withstand seismic stress, or filter cakes weighing tons have to be ejected using compressed air, it quickly becomes clear how complex the physical relationships are. This is precisely where modern simulation technologies, which have become indispensable in mechanical engineering, come into play.

A project with BOKELA GmbH, a manufacturer of filter systems, illustrates how finite element methods (FEM) and computational fluid dynamics (CFD) interact. When using a disc filter in an earthquake-prone area in Greece, it was necessary to ensure the safety of the system. Using FEM analyses in accordance with Eurocode, Merkle CAE Solutions was able to prove that the filter remains stable even under horizontal accelerations of 2.84 m/s². All relevant components were below the permissible deformations, and the screw connections were loaded to a maximum of 89%. This confirmed the earthquake safety of the system beyond any doubt.

While FEM evaluates mechanical behavior, CFD focuses on flow processes. The decisive factor was whether all cells of a rotating unit were supplied with air evenly when the filter cake was removed by compressed air blasts. Using a high-resolution CFD model with 17 million volume elements, the CFD experts at Merkle CAE Solutions analyzed the flow distribution, backflows, and pressure conditions. The result: an even, stable supply, even at increased speeds; the cause of the irregularities observed was not due to aerodynamics.

In a further step, the multiphase flow of air and water was investigated. The aim was to determine the effects of residual liquid in the system. Although the simulations confirmed a slight influence – an approximately three percent higher air content in a cell – the effect proved to be moderate and operationally uncritical.

These projects exemplify the importance of simulation. It enables realistic risk assessment, performance optimization, and visualization of complex processes. What used to require costly prototype testing can now be simulated virtually—faster, more precisely, and more economically.

For companies like BOKELA, this means greater design reliability, shorter development times, and higher operational reliability. For Merkle CAE Solutions, it shows that the use of multiphysics, such as the combination of FEM and CFD, is an integral part of modern engineering work. Because when there is a crash in the filter, simulation determines whether a problem arises or is solved.