I am trying to conduct a wind tunnel test with the Mercedes Bionic Car to determine the drag coefficient, but I'm encountering issues with the simulation setup

Project Support
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thats the url: https://www.simscale.com/workbench/?pid=5471294124236112237&mi=spec%3A584a5f88-1976-4343-9559-952abb21aeba%2Cservice%3ASIMULATION%2Cstrategy%3A7&ps=analysis%2FsimulationControl

I am trying to conduct a wind tunnel test with the Mercedes Bionic Car to determine the drag coefficient (Cd), but I am encountering various issues during the simulation setup. The idea is to create a box around the vehicle, where the box is defined as air, and the walls of the box are assigned different boundary conditions (Inlet, Outlet, Wall).

Steps so far:

  1. Modeling and Setup:
  • The Mercedes Bionic Car was imported as solid2 into SimScale, and the surrounding box was defined as solid1, with the box assigned the material “Air.”
  • The walls of the box were assigned as “Wall” boundary conditions, except for the Inlet and Outlet sides, which were assigned the respective boundary conditions.
  • The vehicle itself was assigned as “Wall” without a material, as it is not the medium (air), but just the boundary for the flow.
  1. Problem Statement:
  • An error occurs when the vehicle is assigned as “Wall” without a material. SimScale requires a material for each object, which leads to a conflict, as only the box has been assigned the air material.
  • If the vehicle is assigned material (air), another error occurs, as only one material is allowed in a region, violating the rules for defining a simulation domain.

Summary of Current Challenges:

  • The issue lies in the assignment of the correct boundary conditions and materials, as SimScale requires each body or surface element to have a material assigned.
  • It is very important to receive a response as soon as possible to resolve these issues and successfully run the wind tunnel test.

thanks for every help

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Hi @jmaurer, thanks for posting on the forum and welcome to the SimScale Community :handshake:

Since you’re doing an Incompressible analysis, you should only insert the fluid part of the domain as this solver does not take into account any sort of fluid-solid interaction. We have this tutorial on our website which has proven useful to many users with a similar application:

Could you try replicating the steps there and let us know if the issue persists?

Cheers
Igor

3

Hi Igor,

Thank you for your quick response and the link to the tutorial. Unfortunately, it didn’t help as I don’t need to set up the simulation as precisely as described in the tutorial, and despite following the steps, the errors are still occurring.

I have defined the fluid region correctly and set the vehicle as a “Wall” with no material assigned, but the simulation still shows issues with the assignment of boundary conditions and materials. Could you please take another look at this and help me out?

This is the link: https://www.simscale.com/workbench/?pid=1585676123629770&mi=spec%3A0951ab23-76b7-4912-a345-f6ef892da0b3%2Cservice%3AMESHING%2Cstrategy%3A8&sh=7

I would really appreciate any further assistance!

Best regards
Jonas

4

Hi @jmaurer,

Thanks for the follow-up! Here’s a quick recording with some comments:

Let me know if this helps!

Cheers

5

Hi Igor,

Thank you very much for your detailed help and suggestions! I’ve been working on the setup, but I encountered a couple of points I wanted to clarify:

  1. When I select the body (the car) and choose “Delete,” the car disappears completely from the simulation. I’m not sure if this is expected or if I might be doing something wrong.
  2. I’ve also adjusted the flow volume to be larger, but I didn’t use precise values like three times the car’s width or similar proportions. Would this still be acceptable for the simulation?

Here’s the link to my project for reference: https://www.simscale.com/workbench/?pid=6954858054197385877&geo=ec946d9c-720b-4a13-af8b-3c00ab7fc67d

I’d appreciate it if you could take another look and let me know if everything seems fine.

Best regards,
Jonas

6

Hi @jmaurer,

The car doesn’t “disappear”, it’s walls are still present which can be seen if you set the surfaces to translucent:

image
image1920×945 57.4 KB

Keep in mind that the flow region is simply an imaginary volume where the fluid would be contained - so it would be a box including the negative of the car.

Well, there is no need to follow the exact value provided in the tutorial - it’s just a general suggestion so that the boundaries don’t influence the flow near the region of interest (which may very on a case-by-case basis).

Cheers
Igor

7

Hello Igor,

Thanks for your help. I ran the test and now its finished but i dont know what to do next. I only need the drag coefficent.
Can you please help me.

Here is the link: https://www.simscale.com/workbench/?pid=6954858054197385877&mi=run%3A8%2Csimulation%3A5&mt=SIMULATION_RUN

best regards
Jonas

8

Hi, make sure to have a look at existing documentation pages: How To Analyze the Pitch, Lift, and Drag Coefficients | SimScale

Cheers