In honor of America’s Independence Day, we decided to simulate an aerial fireworks display in SOLIDWORKS Flow Simulation.  We wondered just how closely we could recreate the effect, and we also had a few specific questions to answer; such as how much the wind will move the shell off course, and what impact the angle of the tube will have on the final trajectory.  We’ll use this information to plan a big fireworks display in SOLIDWORKS and in the back yard.

Let’s run through the setup of the first study.  We need a simple model of a tube to start; even a simple representation will work because the real activity is taking place in the air above.  Before we can launch the shell and see how it is affected by wind, we need to setup the environment with an external flow study.  Using the study wizard, we’ll specify an external study with gravity, air, and a slight breeze to simulate our launch zone.

After the wizard is completed and the environment is set, the only additional step is to define the Computational Domain to be large enough to encompass the shell.  This can be done graphically on screen, by dragging the arrow handles or by editing the definition of the domain; just make sure it is big enough for the blast diameter.  Once the domain is set, simply run the study.

Flow Simulation can inject spherical particles into a completed flow result using a Particle Study.  We more commonly use this tool for dust, mist, or sediment in engineering flows, to see how it will be distributed or where it might settle and create a residual deposit.  Here we’ll use it to simulate a single shell being launched up into the air, and then again to see where the various particles go after they are ejected from the shell.  The Particle Study setup is easy, with another simple wizard prompting the user for required inputs.

Since the particle is being injected into a flow environment that is already solved, it calculates very quickly.  The shell position is shown graphically in SOLIDWORKS, or can be exported to data curves in Excel for further analysis.  Knowing the time delay of the fuse, we can quickly find the shell coordinates when it explodes.  To simulate the burst, we’ll create a spherical model of the shell at the shell burst coordinates and use it to generate a new study.  Since the burst happens inside the original domain, but is limited to a much smaller area, we’ll use a sub-study to calculate the burst more quickly and with more detail.  In Flow Simulation, this is called a Transferred Boundary Condition. It sets the ambient environment to be identical to the result of a previous calculation.

The burst is a very sudden event that creates a violent flow and shock wave. Just because we can simulate the explosion accurately, doesn’t mean it is going to be the best way to approach our current challenge.  Add an outward velocity from the shell of nearly the speed of sound, to simulate the conditions the particles are likely to see.  This saves on computation time and still gives an accurate initial particle velocity. The burst itself has minimal effect on the particle once it is ejected. Run one more particle study to calculate the location of the stars.

Watch the entire video here to see the rest of the process along with the result.  Contact us if you want a copy of the finished assembly so you can run your own fireworks display using SOLIDWORKS Flow Simulation.

MLC CAD Systems

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