# Effect of vent ratio on the drag coefficient of round parachutes

• I
• prithika
In summary: I don't know if there is a specific simulation that can achieve this purpose, but you might be able to use a code or a software that can approximate the drag.
prithika
TL;DR Summary
CFDs or pre-written codes that would help measure the effect of vent ratio on drag coefficient of parachutes.
For my 12th grade school project, I'm planning to research on the effect of vent ratio on the drag coefficient of round parachutes. My idea was to make small model parachutes and drop them from a height, and derive the drag coefficient after certain assumptions. But I also thought it'd be interesting to build a wind tunnel and compare the results from both experiments. However, I'm not sure how to collect drag values from a home made wind tunnel. I'd also like to use a virtual wind tunnel or CFDs to obtain more accurate results and compare my experimental data. Are there any easy CFDs using which I can model round parachutes or any pre existing code that could achieve the same purpose? I'm planning to focus on the effect of the round parachute while descending, not during inflation as it would complicate the process.

Welcome, @prithika !
Are you familiar with terminal velocity?

https://en.wikipedia.org/wiki/Terminal_velocity

A wind tunnel should no give you the results that you expect, because the airstream velocity naturally adjusts to the coefficient of drag (Cd) for each chute-vent configuration.

Lnewqban said:
Welcome, @prithika !
Are you familiar with terminal velocity?

https://en.wikipedia.org/wiki/Terminal_velocity

A wind tunnel should no give you the results that you expect, because the airstream velocity naturally adjusts to the coefficient of drag (Cd) for each chute-vent configuration.
Oh, so the drag coefficient stays constant in a wind tunnel while the terminal velocity is the one that differs? Is there any other method I can use to find out the effect on the drag coefficient without wind tunnels?

Yes, that is the way it works.
I don’t know other ways than experimenting and measuring terminal velocity for each case.
Let’s wait for members with experience in simulation.

You need only build one parachute with a too small vent hole. Measure the terminal velocity, enlarge the hole, measure again, repeat. Terminal velocity is easy to measure with a cell phone video camera, and software that allows you count the number of frames as it passes two marks a known distance apart. The marks can be as simple as the top and bottom of a window in the building where you drop it off an upper floor.

Note that you need the experimental results to calibrate and verify the simulation. And if you have the experimental results, do you still need the simulation?

Some good information on parachutes and vent areas: https://web.wpi.edu/Pubs/E-project/...ighenti_Duffen_Head_Vented_Parachutes_MQP.pdf. The book Fluid-Dynamic Drag, by Sighard F. Hoerner has a few pages on parachutes. Good search terms to find more good stuff are drag characteristics of parachutes.

Lnewqban
jrmichler said:
You need only build one parachute with a too small vent hole. Measure the terminal velocity, enlarge the hole, measure again, repeat. Terminal velocity is easy to measure with a cell phone video camera, and software that allows you count the number of frames as it passes two marks a known distance apart. The marks can be as simple as the top and bottom of a window in the building where you drop it off an upper floor.

Note that you need the experimental results to calibrate and verify the simulation. And if you have the experimental results, do you still need the simulation?

Some good information on parachutes and vent areas: https://web.wpi.edu/Pubs/E-project/...ighenti_Duffen_Head_Vented_Parachutes_MQP.pdf. The book Fluid-Dynamic Drag, by Sighard F. Hoerner has a few pages on parachutes. Good search terms to find more good stuff are drag characteristics of parachutes.
Thank you so much! I will look into these resources. I think I require the simulation to mainly compare both the experimental values and the expected values, so that I can write a reasonable analysis and evaluation. Is there any simulation that can achieve this purpose?

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