CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Simulating aircraft at High Altitude

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   July 4, 2012, 10:55
Default Simulating aircraft at High Altitude
  #1
UAV
New Member
 
Join Date: Jun 2012
Posts: 3
Rep Power: 5
UAV is on a distinguished road
Hello everyone, this is my first post and is concerning a simulation on an airplane meshed in GAMBIT. I would really appreciate some feedback about my values and help me with my mistakes.

My parameters are these:

- 10.000 m altitude
- Pressure (10k m) = 26437 Pa
- Density (10k m) = 0.4161 kg/m3
- Velocity (velocity-inlet): variable
- Temperature (10k m)= 223.15 K
- Viscosity (10k m)= 1.3067e-05

I do not want to explain my mesh otherwise would take ages, just say it is formed by a large cube involving a cylinder and this involving the aircraft. The boundary conditions are velocity-inlet, interior (for the cylinder), wall (aircraft and cube's faces) and pressure-outlet.

Solver parameters:
- Node-gauss based
- Density-Based
- k-omega SST
- PRESTO
- Second-Order Upwind each parameter

I set Pressure to 0 Pa and when asked, Gauge Pressure to 26437, is it correct?
In Materials section, both density and viscosity are constant values.

Reference Values:
- Area: here is where I have more questions, so far I have been using the projected area (1,0,0) in X-axis, which is the frontal view of the aircraft, with 0.01m of error.
- Length: I have been using the longitudinal length of the aircraft, along the y-axis, but I'm not sure about this.

I think these are the main parameters of the simulation.
I would appreciate any help or feedback from anybody, just need to be sure that I am doing the right procedure, or at least close to it.


Many thanks in advance
UAV is offline   Reply With Quote

Old   July 4, 2012, 11:16
Default
  #2
Senior Member
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 1,098
Rep Power: 19
flotus1 will become famous soon enoughflotus1 will become famous soon enough
Why do you use a "wall" boundary condition on the faces of the cube?
A slip-wall (symmetry) would be better in my opinion.

Since your aircraft might travel at a high speed, effects of compressibility may be important. So you should not use constant values for your fluid properties.
flotus1 is offline   Reply With Quote

Old   July 4, 2012, 12:01
Default
  #3
UAV
New Member
 
Join Date: Jun 2012
Posts: 3
Rep Power: 5
UAV is on a distinguished road
When you say symmetry, you mean the four faces of the tunnel (cube), don't you? I will try this solution, thanks a lot!

On the other hand, the aircraft is not meant to fly at high velocities, just up to 200 Km/h or so. However, flying below 200 Km/h I struggle to balance the Weight with the net Lift force the aircraft generates.
UAV is offline   Reply With Quote

Old   July 5, 2012, 06:16
Default
  #4
UAV
New Member
 
Join Date: Jun 2012
Posts: 3
Rep Power: 5
UAV is on a distinguished road
In addition, when fluent starts iterating, it says Reversed flow in 1000 cells in pressure-outlet, and as iteration goes on it decreases until the warning does not appear anymore.

Plus, if I try Ideal-gas, hence Energy equation = On, Fluent shows another warning saying this settings are not appropriate for Velocity-inlet boundary conditions. Why is that happening?

Thanks in advance
UAV is offline   Reply With Quote

Old   July 5, 2012, 07:39
Default
  #5
Senior Member
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 1,098
Rep Power: 19
flotus1 will become famous soon enoughflotus1 will become famous soon enough
For the warnings indicating reversed flow at outlet cells:

Initialize the velocity field with the inlet velocity. Note that this will only speed up convergence. If the warnings disappear after a few iterations, the simulation is still valid.

For the ideal gas calculations, try using a mass-flow boundary condition instead of the velocity inlet.
flotus1 is offline   Reply With Quote

Reply

Tags
aircraft, density, projected areas, reference values, viscosity models

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Simulating a high pressure flow through a valve Kromagnsss FLUENT 8 July 2, 2010 05:20
simulating high Ra and Pr in pipe f_mahmood FLUENT 0 January 2, 2010 18:50
Simulating high pressure burst flow jakjak CFX 2 November 21, 2007 22:06
High Aspect Ratio elements Flavio CFX 2 November 24, 2006 13:01
Multicomponent fluid Andrea CFX 2 October 11, 2004 05:12


All times are GMT -4. The time now is 02:10.