CFD Analysis of lattice fins

[deleted-669563]

Hi,

I am doing a CFD (Computational Fluid Dynamics) study of SpaceX's grid fins design for my science fair this year. This year is my second year doing a study on said fins but this time I'd like to do better than last year.
Just to bring you up to speed I've included a short description of my projects:

Year 1: A study on the design of the interior lattice of the fin. Square lattice vs triangular lattice. I looked for the fin design that had the highest drag at various mach profiles.

Year 2: A study on the cost/weight efficiency of the grid fins. 3 fin vs 4 fin configurations. I am looking to see if 3 grid fins can produce almost the same amount of drag as the 4 fins at various mach profiles while being cheaper/lighter. So far, it seems that the 3 fin configuration can work.

(I am ignoring whether or not the actuator can take the new load since I don't know anything about it).

I am wondering a few things:

1) I am comparing drag so graphs such as Drag vs Cd, Mach vs Cd, are necessary. What other graphs could I make to make my argument better? I am thinking of adding graphs related to the cost/weight of the materials for the fins but I can't think of what to include on a graph (I already have a rough cost estimate of the material per pound).

2) Somewhat similar to question 1 but what other data values besides drag/cost/weight can I look at to verify my conclusion?

3) When I explained my project to the judges last year, about 90% had no idea what I was talking about. How can I impress the judges with my speech? The outline for my speech somewhat goes like this:

Introduction to SpaceX's goals and the history/usage of grid fins >> Provide a detailed explanation of last year's project (Discuss problems with the CAD, software and meshing errors), and then talk about how said problems were resolved this year (i.e no problems with CAD, finer mesh was achieved, no major errors) for my continuation project >> Discuss Year 2's project, while at the same time discussing major concepts related to my project (bernoulli's principle, meshing, types of drag, etc).

Thanks

[norman40]

Hi AielloTim,

It sounds like you've got some very interesting projects going on. Nice work!

I'm not sure that you need any graphs related to drag other than the ones you noted. But you should include some information about the cost and weight of the fins. What would you put into a graph about the weight of the fins? Do you have information that shows how the weight varies with lattice design or some other aspect of the fin configuration? If so, this kind of graph might be good to include. If you have a small amount of information about weight and cost you might consider putting the data into tables.

When I judge science fairs I'm very impressed when a student conveys a good command of the subject and provides a clear and concise summary of the project. Usually we have about 6 or 7 minutes to talk with each student. So it really is important to get across the main points about your project during your presentation. An effective summary should include a description of what you did, what you observed and what you concluded.

Outlining your speech as you've done is a great idea. That should help you refine your speech to fit within the time requirements. It seems that your outline has a lot of information about last year's project. It's fine to mention your previous project but your current work should be the clear focus.

I hope this helps. Please ask again if you have more questions.

A. Norman

[deleted-669563]

Hi,

So far, increasing the dimensions of the fin (thus increasing material/cost) for the 3 fin configuration increases the drag to the point where its "cheaper" than the 4 fin configuration (aka achieves drag values that are within a 10-15% error range of the 4 fin configuration drag values).

Column (first iteration)
https://imgur.com/a/woFHqrq

Quick table (to be further edited)
https://imgur.com/a/5hJerYl

Perhaps these two would be sufficient to put on the project board just in regards to the cost analysis?

Last year, a couple of judges asked specific questions on fluid dynamic concepts I have never heard of. If this happens again, is it acceptable to plain out say "I dont know"? What would you advise to do afterwards?

How important is it to explain concepts into my explanation? For example, is it completely necessary to explain the different types of drag, what type of drag primarily affects the fin, and then explain bernoulli's principle's relation to said drag?

Thanks again.

[norman40]

Hi AielloTim,

I think the table and bar chart could describe the cost analysis very well. You might try constructing the table so that the 3 and 4 fin configurations are in different rows of the same table. This may make it easier for readers to compare the data.

If you're asked a question and don't know the answer, I think its OK to say so. You may want to research the question later if you want to expand your understanding of the topic. And if your project advances to the another level you'll be ready with an answer.

Including comments on concepts in your speech would show your command of the topic. You may not need to explain all the different types of drag in detail. But you might indicate the type of drag affecting the fin, and mention the other types. Don't be surprised if you get questions about how the types of drag differ.

I hope this helps. Please ask again if you have more questions.

A. Norman