pulsation in external gear pumps.
External gear pumps are used in the production of rubber tyres. The external gear pump pressurizes the rubber before it is extruded into a long strip. The target is to produce a strip with consistent dimensions. However, the external gear pump introduces a pulsation in the pressure and mass flow that translates to a pulsation in the width and thickness of the extruded rubber strip. A simulation is set up, which could be used to predict the behaviour of the pulsation, and thus give an indication of the quality of the extruded rubber strip before any experiments need to be performed.
CFD and experiments
The CFD simulation is performed in 2D, to keep simulation times low. A porous domain with a high resistance is added to the end of the domain to simulate the resistance caused by the extrusion head of the machine. One of the main challenges of the CFD simulation was the mesh. Normally a stationary and rotating mesh combination is used for rotating geometries, but this approach is not possible as the two gears mesh together. Remeshing the geometry for each timestep proved to be very time consuming in both mesh time and simulation time. Additionally the quality of the mesh was not good enough to resolve the high gradients of pressure and velocity between the teeth. To solve this, the meshing software TwinMesh was used.
Using TwinMesh we were able to create a structured mesh for each gear, that is ‘compressed’ between the teeth. The structure and element numbering is kept exactly the same between timesteps, only the rotation and compression is changed. The results of the CFD simulation are shown on the right and predicts the pulsation caused by the external gear pump.
The experimental set-up is similar to the machine from the CFD simulation and was used to validate the simulation results. More information can be found in the elaborate PDF below.
Understanding the internal dynamics of a system can be a complex task, especially when only the output, such as the extruded rubber strip and a pressure sensor in this case, is available. However, the use of computational fluid dynamics (CFD) simulations proved to be invaluable in tackling this challenge. The CFD simulations of the pump provided a clear visualization of the internal fluid dynamics of the rubber, allowing for a deeper understanding of the pulsation behavior. Furthermore, the simulations facilitated the testing of a novel approach to modify the pulsation behavior, which would have been expensive to achieve through experimental testing alone. Remarkably, the simulation results were in excellent agreement with the experimental data obtained subsequently, underscoring the effectiveness of CFD simulations in addressing engineering challenges. This showcases the power of utilizing CFD simulations as a valuable tool in gaining insights and optimizing system performance in complex situations.
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