At the International Conference on Screw Machines 2026, held from 8 to 10 September at TU Dortmund University, Jan Hesse from CFX Berlin Software GmbH presented insights into multiphase CFD simulation of positive displacement machines using Simcenter STAR-CCM+.
The presentation provides an overview of multiphase simulations in positive-displacement machines using Simcenter STAR-CCM+. It outlines which relevant flow phenomena and phase interactions occur in these machines and to what extent they can be represented with the available numerical models. In addition, it demonstrates how the choice of modeling approaches and the mesh resolution influence the quality of the results and the overall explanatory power of the simulation. The time-varying numerical mesh for the working-chamber flow domain, which changes over time due to the rotor motion, is generated using the software TwinMesh.
Using an liquid-injected screw compressor as an example, the complexity of the underlying flow physics is highlighted: in addition to the compressible gas, incompressible liquid is injected into the working chamber for cooling and sealing purposes. The interaction of liquid, gas, and rotor motion results in a highly dynamic multiphase process. While the liquid initially enters the injection region as a continuous liquid phase with a free surface towards the gas, it can break up due to shear and unsteady interactions, forming droplets. These droplets impact the rotor and casing walls and generate a strongly time-dependent wall film, whose distribution and film thickness affect the sealing behavior and, consequently, machine performance. In local clearance regions, low-pressure zones may also occur, promoting cavitation. The prevailing flow regime (continuous phase, dispersed droplet phase, wall film) has a significant influence on heat transfer, sealing, and loss mechanisms.
Simcenter STAR-CCM+ provides various modeling approaches to account for these effects. The presentation shows how these models are applied in practice, which phenomena can be captured, and where limitations and modeling assumptions arise. The range of presented results spans from studies on simplified geometries to the simulation of a fully complex liquid-injected screw compressor.
