The new release of TwinMesh, version 2024 coming in November 2023, allows the CFD simulation of more complex applications:
Reed valves
Reed valves are part of different positive displacement machines, e.g. scroll compressors or rolling piston compressors. Their inclusion in the CFD simulation via a coupled fluid-structure co-simulation, e.g. with Ansys Mechanical, is quite complex and increases the numerical effort substantially.
We succeeded with a simplified approach by pre-simulating the reed valve dynamics in Ansys Mechanical to get tabulated return forces and oscillation frequencies over reed valve opening amplitude. These tables are used in a pure CFD simulation to account for the reed valve motion without the need for co-simulation. The geometry of the reed valve and its true bending are part of the CFD simulation. Furthermore with the new release, the calculation of the reed valve motion is included into User Fortran routines to get a simple but stable and efficient simulation setup, allowing several reed valves with different properties in one simulation. A new tutorial describes the steps towards running a compressor with reed valves.
Oil or water injection
Dry-running compressors could already be simulated with TwinMesh and Ansys CFX in the recent years. But often a liquid is used for sealing, cooling, and lubrication. Unfortunately, compressors with oil or water injection are numerically very demanding: Multi-phase simulations have to solve the phase distribution (via an additional transport equation for the volume fraction), and the local properties of the two-phase mixture like density or viscosity may change spatially and temporally by some orders of magnitude. Therefore multi-phase CFD simulations are less stable, more difficult to converge, and the requirements concerning the mesh quality are higher. We succeeded to fulfil these requirements with TwinMesh. A new tutorial describes how to mesh and setup a multi-phase compressor simulation for Ansys CFX with the free surface model.
Twin-screw vacuum pumps
Twin-screw vacuum pumps consist of rotors with very sharp edges and a high wrap angle that often increases towards the pressure side. Both aspects make the meshing of the fluid regions around the rotors very demanding. In the TwinMesh 2024 release, some new features simplify this meshing process and allow the generation of high-quality meshes for twin-screw vacuum pumps. Furthermore, slip models for velocity and temperature allow the extension of the continuum approach towards higher Knudsen numbers into the slip flow regime, i.e. to lower vacuum pressures.
