External Aerodynamics over Ahmed Body Benchmark with Ansys Discovery in Explore Mode

Hello, this is Ertan Taskin from Ozen Engineering, and in this external aerodynamics study, we will use the Ahmed body as a benchmark case. The geometry is over here, and this is a simplified car geometry with the tires and the front end.

In this application, we will use Ansys Discovery in Explore mode to perform the geometry, create the model, perform the simulations, and post-process the results. Let's review the model and the corresponding model settings.

As you see, we are using just half of the body and we are considering two different air volumes, air domains: the inner domain as well as the outer domain. The settings are: we use air, and we set different settings for the walls.

Before going to the walls, the inlet is provided from the left-hand side of the model as the velocity inlet, and the pressure outlet with zero pressure is provided on the far right side of it.

Symmetric condition is imposed on this particular wall, as you see, and the car and the floor are considered as non-slip. The top and the side of the bigger volume are considered as freezer wall conditions.

And so, for this particular study, we will utilize the advanced fidelity adjustments option, and that's actually shown on your screen here with different settings on different locations.

As you see, let me zoom in here, as you see the box, the inner box is set with 0.015 meters, and the surface of the body, as well as the corresponding ground portion, is set to an order of magnitude smaller value than that.

And those can be introduced into the model from here on the top manner, global or the local, and these are the local fidelity adjustments that we put here. The operating conditions, the velocity conditions, are provided as the parameters for the velocities varying from 20 m/s to 60 m/s.

And the calculations are performed considering all these four conditions. After setting these, in order to complete the calculations for all, we have to get here and update the defined variations.

As you see on your screen here, the simulation is completed with the calculated pressure drop, the maximum velocity, as well as the drag force on the body.

So, these calculated drag forces are converted into the drag coefficients, and these drag coefficients are compared to the reference values, and the percentage errors are shown here.

As you see, the errors vary from 1 to 10. This demonstrates that even with the Explore mode, the calculations are in significantly good agreement with the reference values.

One thing to remind is the system fidelity, the overall simulation fidelity, was actually about 15% of the entire full fidelity.

And due to using high fidelity in the local regions, we didn't need to bring this fidelity slider all the way to the right to increase the fidelity to increase the overall simulation fidelity. Even with these settings, the simulations agreed well with the reference values.

So, let's explore the post-processing after these. So, on the right side of the screen of Discovery, we have different options to use for visualization purposes. For example, we can use vectors, and we can choose where to start the vectors from. Let me zoom in to the main region.

Or we can take a look at the streamlines. I brought the streamline initial point all the way to the front of the device with a smaller size of the circular region where the streamlines are initiated from.

And the three-dimensional aspect of the flow features are pretty much captured as you see when I rotate the model. You can definitely feel that.

So, the wake region, which is shown here, is actually pretty much captured with two different distinct regions, and the better view of this can be with the monitors.

So, the X force on the body, which is kind of highlighted here for this 60 meter per second velocity condition, is calculated after the simulation. Once we change the flow velocity condition, it's going to update itself, and we're going to get the new value here.

Let's take a look at the simulation options, and let's take a look at the turbulence model. The K-Omega SST turbulence model was utilized for these calculations. And you can always check the units, and you can make modifications on the units in terms of even the significant digits.

So, this concludes the Ansys Discovery application for the external aerodynamics. Please contact us at https://ozeninc.com/contact for more information.