difference between real-life result and CFD result

[Anonymous]

Hi,

I use CFD to predict the pressure drop of a device. However the difference between the real-life result and CFD result is around 1KPa, which is big.

My device has a capsule inside, and it's motion is driven by air.

I tried steady state analysis and transient analysis with free motion

my steady state analysis often underestimate the pressure drop, whereas my transisent analysis always overestimate it.

in transient analysis I have a time step size of 0.0001, and run for 200 iterations (it took 6 hours normally), and I use the static pressure at the inlet as my result (outlet=0Pa)

anyone know the possible cause of this?

Thanks,

Gubing

[Jon.Wilde]

What is your expected result?

Have you looked into mesh refinement?

What is your Mach number? I ask to be sure you are running the correct set up.

Thanks!

Jon

[Anonymous]

Thanks Jon, yes, for example I set up one of my models according to: http://help.autodesk.com/view/SCDSE/2016/ENU/?guid=GUID-FAF6581B-5FFB-4BAB-91DF-10BA8D35CC62

and this is the screenshot of my model with the settings. The pressure drop from CFD is -3.4KPa, but in real life is 11.2KPa.

I feel this is due to my settings not CFD software, if it is hard to figure out the cause from the support file, I am very happy to talk to you or one of your colleagues through phone 🙂 

CFD 2016 Analysis Setup
Length Units: meter
Coordinate System: XYZ

Geometry Operations:
---None---


Materials:
3 ***Fluid*** Air
Assigned to:
3 CFDCreatedVolume
Properties:
Reference Pressure: 101325 Pa
Reference Temperature: 19.85 Celsius
Gas Constant: 287.05 m2/s2-K
Density Equation of State
Viscosity Constant 1.817e-05 Pa-s
Conductivity Constant 0.02563 W/m-K
Compressibility Constant 1.4
Specific heat Constant 1004 J/kg-K
Emissivity Constant 1
Wall roughness Constant 0 meter


Motions:
---None---


Boundary Conditions:
Boundaries:
#165 Surface
Volume Flow Rate(60 l/min)
#166 Surface
Pressure(0 Pa Gage)
#167 Surface
Pressure(0 Pa Gage)
#168 Surface
Pressure(0 Pa Gage)
#169 Surface
Pressure(0 Pa Gage)
Regions:
---None---


Initial Conditions:
Boundaries:
---None---
Regions:
---None---


Mesh Sizes:
Automatic mesh sizing:
Global resolution: 1.000
Local stretching: 1.100
Minimum points/edge: 2
Points on longest edge: 10
Surface limiting aspect ratio: 20
Auto-mesh log file name: E:/Gubing Wang/cud_0002_fv11/CUD_0002_FV13/Scenario 1/Scenario 1.meshlog
Suppression set for parts:
1, 2

[Jon.Wilde]

Can you share a support file? (CFZ)

Thanks!

[Anonymous]

I tried, the support file is too large to upload, sorry


________________________________

This e-mail was sent by GlaxoSmithKline Services Unlimited
(registered in England and Wales No. 1047315), which is a
member of the GlaxoSmithKline group of companies. The
registered address of GlaxoSmithKline Services Unlimited
is 980 Great West Road, Brentford, Middlesex TW8 9GS.

[Jon.Wilde]

Autodesk 360/Dropbox/Wetransfer? Happy to help but I think I need to see what you're running 🙂

[Anonymous]

Thanks Jon, but our company don't use cloud system, I am going to create a case for it?



________________________________

This e-mail was sent by GlaxoSmithKline Services Unlimited
(registered in England and Wales No. 1047315), which is a
member of the GlaxoSmithKline group of companies. The
registered address of GlaxoSmithKline Services Unlimited
is 980 Great West Road, Brentford, Middlesex TW8 9GS.