# RD-E: 0602 Fluid Flow

Fuel tank overturning with simulation of the fluid flow. The reversing tank is modeled using horizontally-applied gravity. The tank container is presumed without deformation and only the water and air inside the tank are taken into consideration using the ALE property formulation, Iale=1.

The fluid flow is studied during the fuel tank overturning. This example uses the ALE (Arbitrary Lagrangian Eulerian) formulation and the hydrodynamic bi-material law (/MAT/LAW37) to simulate interaction between water and air. The tank container is presumed to be without deformation and it will not be modeled.

## Options and Keywords Used

• Fluid flow simulation and ALE formulation
• Brick elements
• Hydrodynamic and bi-phase liquid gas (/MAT/LAW37 (BIPHAS))
• ALE boundary conditions (/ALE/BCS)
• Gravity (/GRAV)
• ALE property formulation with Iale=1
Regarding the ALE boundary conditions (/ALE/BCS), constraints are applied on:
• Material velocity
• Grid velocity

All nodes inside the border have grid and material velocities fixed in the Z direction; the nodes on the left and right sides have a material velocity fixed in the X and Z directions, while the nodes on the high and low sides have a material velocity fixed in the Y and Z directions. The grid velocity is fully fixed on the border, just as the material velocity is fixed on the corners.

A function defines gravity acceleration in the X direction compared with time to simulate the rotation effect. Gravity is activated by /GRAV. Two cases are studied depending on the acceleration function selected:

## Input Files

Before you begin, copy the file(s) used in this example to your working directory.

## Model Description

A rectangular tank is partially filled with water, the remainder being supplemented by air. The tank turns once around itself on the Y-axis. The overturning is achieved by defining a gravity field in the X direction, which is parallel to the liquid gas interface. All gravity is applied in other directions. The initial distribution pressure is already known and supposed homogeneous. The tank dimensions are 460 mm x 300 mm x 10 mm.

The example deals with two loading cases: an instantaneous rotation of the fuel tank by 90 degrees (gravity function 1) and a progressive rotation (gravity function 2).

The main material properties for the ALE bi-phase air-water are:
Material Properties
Values
Air density
1.22x10-6 $\left[\frac{g}{m{m}^{3}}\right]$
Water density
0.001 $\left[\frac{g}{m{m}^{3}}\right]$
Gas initial pressure
0.1 $\left[\mathrm{MPa}\right]$

### Model Method

The bi-material air-water is described in the hydrodynamic material law (/MAT/LAW37). See previous section for information about this law, including full input data.

This loading case does not require a tank container mesh and the model, air and water are only comprised of the brick element using an ALE formulation.

Using the ALE formulation, brick mesh is only deformed by the tank deformation, the water flowing through the mesh. The Lagrangian shell nodes still coincide with the material points, while the elements are deformed with the material: this is the Lagrangian mesh. For the ALE mesh, nodes on boundaries are fixed to remain on the border, while the interior nodes are moved.

## Results

### Conclusion

This example studied hydrodynamic bi-material using LAW37 in Radioss, using ALE formulation is used. The application of boundary conditions in ALE formations and handling the fluid-structure interaction were discussed. Furthermore, the results obtained correctly represent the physical problem.