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Extending GMO in FLOW-3D

This article highlights fluid structure interaction modeling extensions being developed for the next release of FLOW-3D.

Every day, we naturally select our environment as our reference system. Since our world is rotating on its axis, revolving around the sun and moving with the galaxy through the universe, it is a non-inertial reference system in the language of dynamics. Although we hardly feel these non-inertial effects, they do affect us. Similarly in CFD applications, for convenience of flow analysis, engineers may need to set up a reference frame such as a sloshing tank, a moving boat, an accelerating rocket, or an orbiting satellite. If the reference frame possesses absolute acceleration, it is non-inertial, and the non-inertial effects on fluid and object motions usually cannot be ignored.

FLOW-3D CFD simulation of sticky particles using fluid structure interaction
This series of images shows "sticky"
particles adhering to moving sphere


FLOW-3D CFD simulation showing boiling colored by fluid fraction
Fluid fraction shows boiling


Flow simulation showing temperature distribution inside a brick using FLOW-3D CFD software
The temperature distribution
inside the brick is shown

For the next release of FLOW-3D, the development team at Flow Science has improved the General Moving Object (GMO) model to allow object motion in any non-inertial reference system. In addition to gravitational, hydraulic and other physical forces, all non-inertial forces are considered to account for the non-inertial effects, including forces due to translational and angular accelerations of the reference frame, centrifugal force due to reference frame rotation, and Coriolis forces due to both object motion and reference frame rotation. This allows users to set a reference system on any moving container or equipment to study object motion and its coupling with fluid flow. As with the scheme for defining the motion of a general moving object, the motion of the container itself can be either prescribed or be coupled with fluid flow.

Another extension for the GMO model that our developers have been pursuing is the addition of heat transfer. In the intial version of the GMO model, all objects were assumed to be adiabatic. With the modifications prepared for the next release, heat conduction inside moving objects and heat transfer with fluid and other objects can be calculated. A thermal energy convection term due to object motion has been added to the classic conduction equation. It is discretized by a second-order monotonicity preserving method. Test results show that this methodpossesses much lower numerical diffusion of thermal energy than a first order upstream method thus can maintain temperature profile inside moving objects with quite good accuracy. Two series of images are given from a simulation of a steel brick at temperature 2100 K (1827 C) dropping into water at 90 C. The physical time is 1.5 sec.

Interactions between particles and moving objects have also been improved. Now, when particles collide with a moving object, they are allowed to be stuck on the moving object surface. Existing options for particles bouncing off the object surface can still be used with the user's selection.

Yet another extension of FLOW-3D's GMO model, which will be finished soon, is mass sources and sinks fixed on moving object surfaces. This feature will allow users to simulate fluid emerging from or entering a moving object.