Build my own virtual wind tunnel

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Discussion Overview

The discussion centers on the feasibility and methodology of building a computer-simulated wind tunnel for predicting the drag coefficients of rockets and bullets at both subsonic and supersonic speeds. Participants explore existing software options, computational limitations, and the complexities of simulating fluid dynamics for gaming applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses a desire to create a wind tunnel simulator capable of handling particle physics but questions the feasibility of simulating molecular interactions due to CPU strain.
  • Another participant warns that the computational requirements for accurate simulations may be prohibitively expensive.
  • Some participants suggest that simplifying the simulation could lead to results that lack real-world relevance, emphasizing the challenges of achieving meaningful accuracy without advanced computational resources.
  • There is a discussion about the difference between Computational Fluid Dynamics (CFD) and simplified models used in video games, with a participant questioning the original poster's goals.
  • One participant proposes a method of creating a simplified drag model based on shape and Mach number, suggesting that intuitive approximations could be sufficient for gaming purposes.
  • Several participants mention existing free online wind tunnel simulators and resources, indicating that these might be useful for the original poster's objectives.
  • The original poster shares their experience with integrating drag coefficient formulas into their software and references previous threads for additional context and validation of their simulator's outcomes.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of creating an accurate wind tunnel simulation on standard computers. While some suggest that simplifications can yield useful results for gaming, others argue that significant compromises would render the results unreliable. No consensus is reached regarding the best approach to take.

Contextual Notes

Participants note limitations related to computational power, the need for simplifications, and the potential disconnect between simulation results and real-world physics. The discussion highlights the complexity of accurately modeling fluid dynamics, particularly at varying speeds and with different geometries.

Who May Find This Useful

This discussion may be of interest to individuals involved in game development, physics simulation, or those exploring the principles of fluid dynamics and drag coefficients in various applications.

darkdave3000
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I want to build a computer simulated wind tunnel. I have experience building physics simulators. I undersand that there are already some existing free wind tunnel simulators out there, but do they work at supersonic speeds?
I want to predict the drag coefficient of various rockets and bullets at various speeds both sub and supersonic speeds.
Can I do that with free existing software? If not how should I go about to code my own wind tunnel?

I can create particle physics where each particle represents a mole or even a molecule. But I think molecules will be too many and a strain on the cpu. Would I need to give the particles an electrical charge so that they repel each other if too close due to electron - electron interaction?

I can give the particles (representing moles) mass , velocity and momentum. I can also feed similar properties into the object in question.

Once I work out the Drag coefficient for various bullets and rockets at various speeds I will add rockets and bullets into my "what if" simulator. I can then make a simple game out of it.
 
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You may find that the spec of a computer which can do this job turns out to make it too expensive for you.
 
sophiecentaur said:
You may find that the spec of a computer which can do this job turns out to make it too expensive for you.
I can decelerate time in the simulator and increase number of particles and leave the computer on over night for a more accurate solution.

Otherwise the solution doesn't need to be perfect.
 
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People get supercomputer awards in the millions of hours for this. "Overnight" might not cut it.
 
its not for the airforce
just for a simple gaming sim.
 
darkdave3000 said:
its not for the airforce
just for a simple gaming sim.

The does not matter. There are limits to how much you can simplify things and still get sensible answers; and the only way to to do these simulations on a normal computers would be to simplify things to the point where the the numbers you would get out would have no relation to reality whatsoever.; at least if you want your simulations to work with generic geometries. You would be better off just looking things up in a table or just guessing.
 
darkdave3000 said:
its not for the airforce
just for a simple gaming sim.
What you are describing vs what you are saying you want don't match. Solving for a flow condition from scratch in a long-running (hours/days) computation is called Computational Fluid Dynamics (CFD). It is a science/engineering tool that is highly specialized, difficult and expensive. Trying to design a piece of CFD software isn't something you are likely to be able to handle until you are working on your aerospace engineering phd.

Video games, on the other hand, use highly simplified models for aircraft performance in order to provide realtime (30 times a second) performance calculation.

Can you clarify what you are really after?
 
f95toli said:
The does not matter. There are limits to how much you can simplify things and still get sensible answers; and the only way to to do these simulations on a normal computers would be to simplify things to the point where the the numbers you would get out would have no relation to reality whatsoever.; at least if you want your simulations to work with generic geometries. You would be better off just looking things up in a table or just guessing.

Sim can be left running for several days, weeks, months there's no limit. The progress can even be saved and resumed to match the performance of a super computer running at proportionally shorter time frames while maintaining as many variables/particles needed to get practically useful and accurate values.

Also there are already free online virtual wind tunnels some of which were mentioned in this forum:

https://www.physicsforums.com/threads/drag-calculation-in-3d-virtual-wind-tunnel.133939/ Are you saying they have no use either?

Purpose: I want the Drag coefficients of rockets and bullets at various speeds from 0 to mach 5 for several gaming sim projects. Also for mortars and artillery shells and grenades from grenade launchers. With a virtual wind tunnel I can work them out instead of being at the mercy of the internet for available info.
 
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So... yeah I would just make it up. You can design a fake wind tunnel which might give realistic/intuitive results. Take these simple drags and when the mach number increases, increase the drag. So if you put 1 shape in, the game just increases the drag a set amount. If you have a weirdly shaped object, just count the number of squares and points for example. If it is a rough surface, make it turbulent flow. If it goes very high mach number, increase the drag a lot due to chemically reacting flow.
I think its your best bet.
 

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fahraynk said:
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So... yeah I would just make it up. You can design a fake wind tunnel which might give realistic/intuitive results. Take these simple drags and when the mach number increases, increase the drag. So if you put 1 shape in, the game just increases the drag a set amount. If you have a weirdly shaped object, just count the number of squares and points for example. If it is a rough surface, make it turbulent flow. If it goes very high mach number, increase the drag a lot due to chemically reacting flow.
I think its your best bet.

I don't think it will come to reading that many pages, but I would prefer to do the research, I think I have gathered enough keywords from this thread and another:

https://www.physicsforums.com/threads/drag-calculation-in-3d-virtual-wind-tunnel.133939/

already to get started reading on wikipedia on the related topics:

1. Reynolds Number
2. Computational Fluid Dynamics
3. Drag Coefficient
4. Stokes Formula (need elaboration on this) "Diff Eq form of the Navier-Stokes fluid flow equations,"
5. Any further suggestions from this community will be appreciated

The thread also gave me a few leads with existing software simulated wind tunnels:

"There seems to be several (free) 3D Navier-Stokes solvers in the net, e.g.

http://fun3d.larc.nasa.gov/chapter-1.html
http://wissrech.iam.uni-bonn.de/research/projects/NaSt3DGP/index.htm
http://www.fenics.org/
http://www.opencfd.co.uk/openfoam/index.html#openfoam
"
I am yet to check them out to either use them for calculating Drag Coefficients at various speeds(subspnic and supersonic) of rockets and bullets and/or use them as a base to create my own simulated wind tunnel.

Usually with programming in scientific behaviours into simulators I skim through the materials and look for one or two formulas that will be programmed into the software as a key algorithm. I would also need to know how to use the formula correctly so once I find what I am looking for I do more reading and research surrounding the formula so I can put it into context. In my other thread:

https://www.physicsforums.com/threa...t-ball-shot-bullet.910655/page-2#post-5753842

I was trying to find the formula for predicting changes in the Drag Coefficient for a sphere at various speeds and successfully integrated this into my software, the screenshots of which are available on yet another thread

https://www.physicsforums.com/threa...sing-at-supersonic-speed.913205/#post-5753621

I created to try and get confirmation of certain interesting outcomes of my simulator on the Hiroshima Mushroom cloud which appeared to be rising at Mach 1 in my simulator and at times slightly beyond Mach 1. Turns out there is some evidence that my simulator was correct in predicting a supersonic mushroom cloud that broke the sound barrier and thus created secondary shock-wave independent of the blast.

The supersonic ball of hot gas rising in the mushroom cloud was assumed to be a sphere so the drag formula as well as buoyancy related formulas simulated a supersonic "ballistic" mushroom cloud which another community member verified has been observed in reality by citing a scientific article.

Now I want to do the same for non spherical shaped objects, should I use the same formula I used to adjust the Drag Coefficient for the sphere for non spherical shapes as a rough approximation to save my self the trouble of building a simulated wind tunnel?
http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2059.pdf

David Ong
Portfolio/CV
Http://Simulti.Tech
 
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