Mixture Multiphase with Large Scale Interfaces: Gear Lubrication

The Mixture Multiphase (MMP) model is suitable for modeling dispersed multiphase mixtures, where the mixture of phases is represented by weighted physical properties. A single set of conservation equations for mass, momentum, and energy is solved for the mixture together with transport equations for phase volume fractions.

The Large Scale Interface Detection (LSI) model detects groups of cells that contain large interfaces between phases. By the use of the Large Scale Interface Detection (LSI) model, the capability of MMP is extended to model not only mixtures, but also stratified flow. The combination of both models, also known as MMP-LSI, can capture different co-existing flow regimes such as free surface flow, dispersed droplets, and dispersed bubbles. MMP phase interactions do not require fixed dispersed and continuous phases. In some parts of the computational domain, the primary phase can be dispersed, and in another part, the secondary phase can be dispersed.

MMP-LSI lets you simulate multiphase applications such as evaporators, oil pipelines, or nuclear applications at higher CFL numbers, that is, allows a larger time-step and a coarser mesh near the phase interface, without compromising the accuracy of the results with respect to engineering quantities, for example, torque.

This tutorial demonstrates the workflow for setting up an MMP-LSI simulation by using a case of gear lubrication. The following schematic diagram shows the configuration:

Two interlocking gears sit in an oil bath and counter-rotate at high speed. At the beginning of the simulation, the oil phase fills the bottom half of the domain and the air phase fills the upper half. The two phases are separated. The fast rotation of the gears generates oil droplets and air bubbles--a mixture.

The domain is a closed system containing no flow boundaries. The motion of the gears is accounted for by using overset meshes. The gears are interfaced with the overset background mesh boundary. Oil and air are modeled as incompressible liquid and gas. The multiphase mixture is modeled using MMP-LSI with the ADIS scheme for sharp interfaces.

As a result, the volume fraction of oil is animated to illustrate the transient evolution of the oil-air interface. The results highlight the flow regimes of the phases within the domain: stratified and dispersed flow, forming under the influence of the body forces of the rotating gears.