Learning Forum

[MCFDHELP]

When i increase the angle of attack for an airfoil in fluent, the whole free stream increases in static pressure? Does anyone know why this happens?

Thanks

[RK]

Hello,
Can you please elaborate? Could you also insert images of pressure contour which will make us better understand your question.

[MCFDHELP]

Hi
Yes i have attached images. The only thing altered is the angle of attack and the free stream pressure increases massively

[MCFDHELP]

Ignore the attachments, have inserted the photos into the message

[Rob]

Please post images of the outer boundary condition and domain size for both cases.

[MCFDHELP]

The domain length is 320 m and the radius of the ciruclar section is 160m

[MCFDHELP]

I have set the ground as a moving wall, the inlet as the curved and upper section and the outlet as pressure outlet

[Rob]

Check it's the same in both cases.

[MCFDHELP]

yes i have checked it is the same for both cases

[Rob]

Can you probe the second case too? Looking at the scale carefully, you could be looking at the same value but the scale is very different.

[MCFDHELP]

you could be right, is there any way that i could verify this? as the scales are so different

[Rob]

Put a point into the domain and report the facet value. Display-Surface-Point, then use the Surface Report functions.

[MCFDHELP]

i have done what you say, and they all appear to be around -2 to -6 pascals for the static pressure. The angle of attack varies from 0-9 degrees

[Rob]

Which is near enough the same.

[MCFDHELP]

do you know why it is negative?

[MCFDHELP]

or how to change the colours so they all show the same colour for free stream?

[Rob]

It's probably about zero so might be convergence related. In the contour plot deselect the "auto range" and add values manually.

[MCFDHELP]

when i add my own range, it cuts out some parts in white

[Rob]

There's an option called "clip to range". Funnily enough if you have values outside of the manual range they disappear with that ticked.

[Mani kiran]

can anyone help me to write the user defined function for a airfoil as it is landing as similar to the real case secenario 

[Rob]

You will need to be a lot more specific: what are you trying to replicate?

[Mani kiran]

i just want to replicate the landing profile of the aircraft 

as similiar to the mission profile of this 

[Rob]

Do you need to solve the whole decent, or would several steady calculations be equally valid? The former will be a very long transient run, the latter some steady calculations. 

[Mani kiran]

as you can see sir that i wrote a UDF for airfoil which is moving in straight path

 

#include "udf.h"

 

DEFINE_CG_MOTION(airfoil,dt,vel,omega,time,dtime)

 

{

 

  real t=time;

  

 

  vel[1]= -0.025*t;

 

 

}

 

so can u help me to write UDF which is similair to real life 

[Rob]

I'm still trying to understand why. All I'm able to do re UDFs is point you at the documentation. 

[Mani kiran]

i think lets try with using the steady calculations , if its not efficient to what i want to figure out ,then we can proceed with the  long transient run .

[Rob]

Steady will probably be quicker. Use the various NACA airfoil examples (Learning and Fluent Help) for guidance.