# Help with aerodynamic shape considerations

## Main Question or Discussion Point

I have a flow acting perpendicular to a shape ie an airfoil however i dont think an airofoil is the best shape for the flow not to recirculate too much was wondering if anyone has any ideas? please view my attachment for basic drawing of the problem

thank you

engineering

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Whenever there is a flow obstruction perpendicular you will probably see separation/recirculation. May I ask what is the application, Reynolds number etc you are looking for? Your problem statement is rather vague.

Danger
Gold Member
I didn't want to be the first respondent here, since I don't really know anything about it, but I agree that the question is a bit vague. Are you looking to minimize the aerodynamic effects upon a necessary structure? Or are you trying to introduce a structure to alter airflow in some particular way?

I am trying to minimize turbulence so i would like the Reynold number to be lower than the turbulent value of reynold number.

Danger
Gold Member
Okay, two more questions, then. Is the airflow always going to be impinging upon this structure from the same direction? What about variations in speed?
My first thought is that some variation of a 'teardrop' cross-section would be best, but I'm no expert.

yes the shape is always going to be impinging the airflow the velocity of air varies from 100 meters per second up to 300 meters per second

Danger
Gold Member
Wow... that's a lot faster than I expected. There might be some trans-sonic flow problems that change things at the higher end of that range. Fred or Russ are probably the best guys to handle this.

At that speed I doubt your Reynolds number will be less then turbulent! Also is this in a duct, or open channel flow. In the first case the Reynolds number should be less then about 1200 for laminar flow.

First off, those are very high velocities. High enough that you cannot consider the flow incompressible. So that makes this more complicated already.

Second, if the impingement has to be perpendicular to the flow then what exactly are you trying to change?

My only suggestion would be to streamline the side opposite of the incoming flow. This will reduce drag and likely reduce (to some degree) some of the turbulence.

What are you looking to do with this device?
What is the height (into the flow) of the bump relative to its length (parallel to the flow)?

the device is use to introduce some form of liquid into the flow i haven't any specific specifications for the design just thinking about the shape trying to bea s aerodynamically sensible as possible.

russ_watters
Mentor
Second, if the impingement has to be perpendicular to the flow then what exactly are you trying to change?

My only suggestion would be to streamline the side opposite of the incoming flow. This will reduce drag and likely reduce (to some degree) some of the turbulence.
That's exactly what I was thinking. Just build a fairing.