[saikrishna_a]

Hello CFD people,

I am working on some CFD validation project and have some basic doubts related to surface Cp distribution contour. I am a rookie in CFD and learning new things everyday.

1) Does surface Cp distribution plot helps you tp identify the flow separation point on the wing? If yes, can you explain how?

I assume that flow accelerates on the upper surface causing Cp to come down up to a limit and again Cp increases on the surface plot.

2) Why do we see an increase in Cp value downstream on the upper surface?
I attach a Cp contour from one of my results. Can anyone analyse the plot and explain me clearly what is happening to flow? Is it separated or attached until the trailing edge?

[agd]

Before you go much further in CFD, it sounds like you need to dig into basic fluid mechanics a little more. The pressure coefficient is simply a normalized pressure (or pressure difference relative to freestream). So the behavior of the pressure coefficient reflects how the pressure on the surface is varying. Some questions to consider - what drives the flow along the surface? When flow separates what does the pressure do? How is that reflected in the pressure gradient? I would encourage you to do some study in basic boundary layer theory, since most of your questions are basically answered in undergraduate textbooks on fluid mechanics. Here's a little hint - a favorable pressure gradient is defined as dp/dx < 0, where x is the coordinate along the wall. An unfavorable gradient (which helps drive separation) is defined as dp/dx > 0. That doesn't mean that the flow always separates in a region of an adverse gradient, but those are the places you start looking. There's more to look for, and a decent textbook on fluid mechanics will show you what you need to know.

[saikrishna_a]

Thanks agd. Do you intend to say that from a surface Cp contour, we cannot conclude whether the flow is separated?

[agd]

You cannot conclusively determine if flow separates, unless the pressure gradient is favorable over the entire surface. In that case you can say that there should be no separation. You can identify areas worthy of additional investigation. Such an investigation would be to look at the velocity profile and the shear stress distribution. Again, you should probably find a good textbook on fluid mechanics to study.

[FMDenaro]

Originally Posted by saikrishna_a

Thanks agd. Do you intend to say that from a surface Cp contour, we cannot conclude whether the flow is separated?

But why don't you first have a look directly to the velocity field to find separation? And then superimpose your Cp to check the answer?