Bullet (HPBT) movement CFD Simulation by Dynamic Mesh

Bullet (HPBT) movement CFD Simulation by Dynamic Mesh, ANSYS Fluent Training

Description

The hollow point boat tail bullet is primarily a rifle used for hunting big game at long range. In ANSYS Fluent Software, there are different ways to model moving objects. The dynamic mesh is a model in which the elements of the domain reform perish and get generated over time. This model is more tangible than stationary models in which the objects are fixed, and the flow moves.

In this project, a 2D HPBT  ammo in a rectangular domain is designed while the bullet’s velocity is 2850 ft/s. The Dynamic Mesh model simulates the movement of the bullet in which the elements are meshing every time step. The compressibility of the air over the bullet is modeled using the Density-Based option which uses ideal gas material to define the air properties.

There is a bullet with a length of 21mm and a height of 7.92mm in positive X and Y directions. Design Modeler software is used to create the geometry of the solution. ANSYS Meshing software is used for generating meshes, and the elements are all triangles (unstructured) due to the ability of this model to remesh triangle elements. Plus, The number of elements is 13,040.

This CFD project is the 11th episode of the ANSYS Fluent General Training Course.

Methodology: HPBT Bullet (Dynamic Mesh)

The simulation is Transient (unsteady) in order to capture the behavior of fluid over time. The Density-based solver type is used due to the compressibility of the working flow. The speed of the bullet is 2850ft/sec which is exactly equal to the Mach number of 2.531.

That’s a good reason for us to select the ideal gas option for the density of the air to model its compressibility. The gravitational acceleration effects are ignored. Furthermore, The Dynamic Mesh module is employed.

Conclusion

At the end of the solution process, two-dimensional contours of pressure, temperature, and velocity are obtained. Also, the elements are visible at every five time-steps, deforming at the start of each time step.

unlike other models available in ANSYS Fluent software, the bullet is moving, and the air is stationary. The motion of the air pressure and velocity behind the bullet which is formed due to the shock wave, as a result of breaking the sound barrier is considerable. Related animation to the bullet’s movement with the change of velocity in the domain is exhibited.