The concept of vortex interactions came from Prandtl's lifting line theory. His student, Albert Betz, adapted lifting line theory to propellers. However, vortex interactions were never in a working propeller code, until much later. Barnes McCormick was the first to start working on it. A long time ago, I talked to him about his work and he said it wasn't in a working code. The author of PROPSY was the first person to have them in a working code, that I'm aware of. Unfortunately, there were a lot of bugs in that code. I've spent a lot of time fixing those bugs.

I have numerous issues with the concept of vortex interactions:

• They are very difficult to code, which makes them very difficult to debug
• The concept requires time travel (which is a huge red flag)
• They miss situations that have strong blade to blade interactions. For instance, a constant chord turbofan blade will have no bound vortex interactions
• In the case of PROPSY, and earlier works, they included interactions that can never happen. Moreover, vectors that pass through solid objects or the wake of other blades. I've greatly reduced this problem, in PROP_DESIGN. However, I didn't completely remove it
• They do not apply to turbulent flow
• They do not apply to ducted propeller/fans with sweep (airfoil and/or blade). This is because the vectors would ricochet off of the duct walls and come back across the wake (causing turbulence)
• They do not capture pressure effects, which is the biggest thing that you want to capture. So things such as shock waves or the fact that airfoils close together perform differently than when far apart
• The trailing vortex interactions slow the code way down
• Lastly, in my testing, the effect is usually small

For all of these reasons, I removed vortex interactions from the main codes. Because I've spent so much time bug fixing this aspect of PROPSY, I left the feature in three test codes. I think they are useful for educational purposes. I also think that all the time I spent on them could save others a lot of time. In the past, these three codes were in the 'Undocumented Programs' folder of the primary download. Recently, I moved them to their own download. This download is completely optional. The codes are still undocumented. However, if you know how to use PROP_DESIGN, you will have no trouble figuring out how to use these codes.

The topic of vortex interactions is extremely unfortunate. Because Prandtl is so highly regarded, this topic persists. It would have been better if the concept of vortex interactions had never been created in the first place. In my opinion, it's a major waste of time.

Release 06/22/24 Update 1:

Vortex Interactions.zip (links to my 'Proton Drive' account)

Notes:

PROP_DESIGN utilizes a new type of propeller theory that I created in January of 2020. PROP_DESIGN is unproven. It is up to the user to verify his or her designs. To do this, I recommend comparing the results you obtain with PROP_DESIGN against test data that you collect.

After 16 years of continuous improvement, there are no major updates planned. If any at all, future updates will be minor.

I've noticed that other people have posted old versions of my codes. I strongly recommend that you don't use them. There have been thousands of improvements and bug fixes, over the years. The codes from day one are nothing like today.

For information on recent changes, see the 'News' page.