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windywires May 5, 2016 11:09

Interesting pressure and velocity contours
 
I've been analysing the 2D flow over a not-quite-circular cylinder in ANSYS Fluent. The analysis has been transient and run long enough to produce this lift coefficient plot. It oscillates at the vortex shedding frequency as would be expected and its time-average gives a lift coefficient of -0.307.

With this downwards lift in mind, I don't understand these total pressure and velocity magnitude plots. There seems to be higher pressure AND higher velocity on the underside of the shape, which would be impossible according to Bernoulli. Also, wouldn't the higher pressure underneath suggest upwards lift and give a positive lift coefficient? And what can can we interpret from the fact that the shed vortexes take a path at an angle to the flow?

I'd really appreciate your thoughts

davidwilcox May 5, 2016 12:37

Let's have a look at your dynamic and static pressure distribution *wink*

windywires May 5, 2016 13:06

Thanks very much for the reply, David. I don't actually have access to the data right now (it's saved on a lab computer) but I'm assuming you mean that you'd expect there to be an area of high dynamic pressure and low static pressure on the underside of the shape? That makes sense!

Any ideas why the vortices move upwards? Is this because the shape is being 'lifted' downwards?

FMDenaro May 5, 2016 14:02

Quote:

Originally Posted by windywires (Post 598831)
I've been analysing the 2D flow over a not-quite-circular cylinder in ANSYS Fluent. The analysis has been transient and run long enough to produce this lift coefficient plot. It oscillates at the vortex shedding frequency as would be expected and its time-average gives a lift coefficient of -0.307.

With this downwards lift in mind, I don't understand these total pressure and velocity magnitude plots. There seems to be higher pressure AND higher velocity on the underside of the shape, which would be impossible according to Bernoulli. Also, wouldn't the higher pressure underneath suggest upwards lift and give a positive lift coefficient? And what can can we interpret from the fact that the shed vortexes take a path at an angle to the flow?

I'd really appreciate your thoughts

could you better define "non-quite-circular"?

windywires May 5, 2016 14:10

It's got two notches in it - the cross-section can be found here

windywires May 5, 2016 14:20

Filoppo, it's a circle with notches along both sides on the upper half, as shown here. I hope that helps :)


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