# CFD Car Body

**URL:** <https://www.simscale.com/forum/t/cfd-car-body/101442>\
**Category:** Project Support\
**Created:** [November 9, 2026, 5:20pm UTC](https://www.simscale.com/forum/t/cfd-car-body/101442 "2026-11-09T17:20:15Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![cdrt](https://www.simscale.com/forum/letter_avatar/cdrt/32/6_22734026db12803ebb3e059622ac3534.png) [@cdrt](https://www.simscale.com/forum/u/cdrt)\
**Post date:** [November 9, 2026, 5:20pm UTC](https://www.simscale.com/forum/t/cfd-car-body/101442/1 "2026-11-09T17:20:15Z")

</div>

Hello,

I’m trying to apply the simscale tutorial for aerodynamics on a car to a prototype car being designed by us, but the external flow body disappears after creating it. When I try to delete the car body from the volume, I cant see any visual change apart from the car disappearing. Does anyone have any ideas what the issue may be?

[GP Windtunnel | SimScale Workbench](https://www.simscale.com/workbench/?pid=330958438635324890&geo=b4881d11-ddcf-4579-a43c-bb4f660b469b)

 ![image](https://www.simscale.com/forum/uploads/default/original/3X/8/a/8a98fe5353c1e9505b138225a73e0d6732dd750a.png)

---

<div class="post-metadata">

**Author:** ![parm62](https://www.simscale.com/forum/letter_avatar/parm62/32/6_22734026db12803ebb3e059622ac3534.png) [@parm62](https://www.simscale.com/forum/u/parm62)\
**Post date:** [November 10, 2026, 2:00pm UTC](https://www.simscale.com/forum/t/cfd-car-body/101442/3 "2026-11-10T14:00:43Z")

</div>

Hi @cdrt,

This is a common point of confusion when setting up external aerodynamics. Your setup is actually completely correct so far; this is just a visibility and perspective issue in the CAD viewer.

When you use the External Flow Volume tool, it creates the air block and automatically subtracts the car geometry from it. However, because the resulting flow region is a solid, opaque block of air, you cannot see the car-shaped void trapped inside it from the outside.

Here is how to resolve the visibility and verify your geometry:

**1.Apply the Delete Operation:**

Click **Apply** on your current `Delete bodies` setup to remove `Part 1` and `Top Body Shell`. In CFD, you only mesh and simulate the fluid (air), so deleting the solid car bodies after the flow volume is created is the correct workflow.

**2.Unhide the Flow Region:**

If the viewer appears completely empty after deleting the car, go to the scene tree on the right side under `GEOMETRY`. Click the eye icon next to **Flow region** to toggle its visibility on. You will now see the large bounding box representing the wind tunnel air.

_Verification:_ A large bounding box appears in the center of the 3D viewer.

**3.Verify the Internal Void:**

To visually confirm the car was successfully subtracted from the air block, activate the **Cutting Plane** (Section View) tool from the top viewer toolbar. Drag the plane through the center of the box to look inside.

_Verification:_ The cross-section will show a solid area for the air, with a hollow, empty void in the exact shape of your prototype car.

---

<div class="post-metadata">

**Author:** ![cdrt](https://www.simscale.com/forum/letter_avatar/cdrt/32/6_22734026db12803ebb3e059622ac3534.png) [@cdrt](https://www.simscale.com/forum/u/cdrt)\
**Post date:** [November 10, 2026, 6:26pm UTC](https://www.simscale.com/forum/t/cfd-car-body/101442/4 "2026-11-10T18:26:43Z")

</div>

> [@cdrt](#):
>

Hi Parm,

I’ve done this, but the flow region is still not visible and the result doesn’t look the way I think it should.

With the visibility toggle on, all I can see is what I presume to be a random strip from the car body.

Are you able to open the file and see for yourself as I’m not able to post a screenshot in this reply.

Many thanks!