Simulating Ballistics - Computing Coefficient of Drag

[SergejVictorov]

Hello everyone. I'm new to this forum and very impressed so far.

I'm making a program which simulates the flight of an object. In order to do that, I have to compute the coefficient of drag. This is the first problem. From what I know, it should be possible to determine this number (at least approximately) by examining a 3d model of the object.

Second: I'm looking for the function which describes how the coefficient of drag changes with the Mach and the Reynolds number (Cd[Ma,Re]).

I have seen it has been done (http://home.snafu.de/l.moeller/Ballistik/Airdrag.html), but I wasn't able to extract the formulas from the source code.

Has anyone got a suggestion to these questions? Thank you in advance.

 

[eljose79]

Hello and welcome to the forum! It sounds like you are working on a very interesting project. I am a scientist with expertise in fluid mechanics and I would be happy to offer some suggestions for your questions.

To determine the coefficient of drag for your object, you can use a combination of experimental data and computational simulations. You can start by conducting wind tunnel experiments with a scaled model of your object to measure the drag force at different velocities. This will give you an experimental value for the coefficient of drag. Then, using computational fluid dynamics (CFD) software, you can simulate the flow around your object and calculate the drag force. By comparing the results from the experiments and simulations, you can refine the coefficient of drag value for your object.

As for the function that describes how the coefficient of drag changes with the Mach and Reynolds number, there are various empirical relations that have been developed for different shapes and objects. One commonly used relation is the Prandtl-Glauert rule, which approximates the change in coefficient of drag with Mach number for subsonic flows. For the Reynolds number, there are different relations for different types of flow, such as laminar or turbulent. You can find these relations in textbooks or research papers on fluid mechanics.

I would also recommend reaching out to experts in the field of aerodynamics or fluid mechanics for further assistance. They may be able to provide more specific information and guidance for your project. Good luck with your program!