Asking simulation axial flow fan...

teguhtf · December 24, 2011, 18:28

Dear all,
I'm simulating axial flow fan in ventilation case (Exhaust) as my thesis project. I put axial in a duct which is connected to small room. I use 4 blades (type blade NACA 0015), blade angle 10 Deg, 1500 RPM, 4 Inlets (In the bottom of the room) and 1 outlet (In the edge of the duct) [each velocity inlet 1 cm/s and pressure outlet 20 Pa]. I'm using parallel process on Core i7 Memory 8Gbyte. I use MRF model. I have used some setting of turbulent model and solver method. But, my flow rate still in wrong direction. What's wrong with my simulation??

Any body help me please!!
Here i attach some result of my simulastion
Thank you so much
Teguh

PS. Here is my setting
Force Report
Force vector: (0 1 0)
pressure viscous total pressure viscous total
zone name force force force coefficient coefficient coefficient
n n n
------------------------- -------------- -------------- -------------- -------------- -------------- --------------
blade1 1.6001618 -0.020952276 1.5792095 2.6125091 -0.034207798 2.5783013
blade2 1.3231293 -0.021169876 1.3019594 2.1602111 -0.034563063 2.125648
blade3 1.8841036 -0.018701983 1.8654016 3.0760875 -0.03053385 3.0455537
blade4 1.3345512 -0.018644545 1.3159067 2.1788591 -0.030440073 2.148419
------------------------- -------------- -------------- -------------- -------------- -------------- --------------
net 6.1419459 -0.07946868 6.0624772 10.027667 -0.12974478 9.897922

FLUENT
Version: 3d, dp, pbns, rke (3d, double precision, pressure-based, realizable k-epsilon)
Release: 6.3.26
Title:

Models
------

Model Settings
------------------------------------------------------------------
Space 3D
Time Steady
Viscous Realizable k-epsilon turbulence model
Wall Treatment Enhanced Wall Treatment
Heat Transfer Disabled
Solidification and Melting Disabled
Species Transport Disabled
Coupled Dispersed Phase Disabled
Pollutants Disabled
Pollutants Disabled
Soot Disabled

Discretization Scheme

Variable Scheme
------------------------------------------------
Pressure Second Order
Momentum Second Order Upwind
Turbulent Kinetic Energy Second Order Upwind
Turbulent Dissipation Rate Second Order Upwind

duri · December 25, 2011, 13:42

Quote:

Originally Posted by teguhtf

Dear all,
my flow rate still in wrong direction. What's wrong with my simulation??

Can you make clear about what is going wrong?.

Do some general checks like mesh quality and its dimensions, units and after initialization check flow field. If mesh was not created in 'm' then double check the size and units of mesh.

teguhtf · January 3, 2012, 01:36

Thank's for replying
I'm sorry, i have checked it to the literature. My simulation is right.

. But now, my problem is on the blade. I have read that axial flow fan concept is the same as aircraft wing. Aircraft use lift of an airfoil. But, the axial flow fan use reaction force of lift to work (3rd newton law). Based on that, i can conclude that if direction of my flow rate is up, my blade lift must be on the opposite direction (down).
In my simulation, my lift is in up direction, so my flow rate must be in down direction.
I don't know how to fix that.
Thanks a lot.
Teguh

duri · January 3, 2012, 02:58

In axial fan work supplied should equal to the sum of components of drag and lift in theta direction. To know the lift direction, first construct velocity triangle for the fan blade. This gives the local angle of attack, based on this you can figure out the lift direction for the airfoil section. Mostly lift will on the upper surface (suction side). At negative angle of attacks below zero lift angle of attack it will switch direction.
Whether fan or turbine lift and rotation direction can be deduced from geometry itself.

sunflower · January 3, 2012, 05:15

Hi Teguhtf,

The first picture in your attachment looks very nice. Would you please tell me how to create such kind of picture? I mean how to show the pathline together with geometry frame with grey color.

Thanks.

[QUOTE=teguhtf;336943]Dear all,
I'm simulating axial flow fan in ventilation case (Exhaust) as my thesis project. I put axial in a duct which is connected to small room. I use 4

Far · January 3, 2012, 05:51

use mesh overlay

A) display----> scene -----> overlays (make sure it is selected)
B) display----> scene -----> display and then set transparency

Procedure.
1. display mesh (faces) and then set the transparency as required using step B
2. then apply step A
3. display path lines (make sure grid is not selected)

you are done

teguhtf · January 3, 2012, 05:56

Thank you duri
I have done some variation on my simulation i.e. Blade angle 5 deg and 10 deg, inlets and outlet value, and RPM of blades. But the lift is still in up direction. I'm still confused with my velocity triangle because my blades are symmetry. Do you have any reference about it??
Thanks for help
Teguh

D.B · January 3, 2012, 06:13

Hi,
you can check a few things, 1st from your geometry it seems the direction of rotation should be anti-clockwise when seen along -Y to +Y direction and the flow should be from +Y to -Y direction.
It seems from your figure that your blades are at a negative angle of attack, is it my error in seeing ? just check it might help you out.

teguhtf · January 3, 2012, 06:53

Hi sunflower
I'm using FLUENT 6.3. Here is the setting
->To show the geometry frame
Display>pathline>enable draw grid option>grid option> disable edges option and enable faces option>colors>choose wall on type table and choose light gray on colors table>close>click display on Grid display
->To see interior
Display>options>enable all option in Rendering section and enable light on on lighting attribute>apply

If two steps have been done, back to pathline option
then click display
Hope it helps
Teguh

Quote:

Originally Posted by sunflower

Hi Teguhtf,

The first picture in your attachment looks very nice. Would you please tell me how to create such kind of picture? I mean how to show the pathline together with geometry frame with grey color.

Thanks.

teguhtf · January 3, 2012, 06:54

Thank you for your suggestion

I'll check it.
teguh

Quote:

Originally Posted by D.B

Hi,
you can check a few things, 1st from your geometry it seems the direction of rotation should be anti-clockwise when seen along -Y to +Y direction and the flow should be from +Y to -Y direction.
It seems from your figure that your blades are at a negative angle of attack, is it my error in seeing ? just check it might help you out.

duri · January 4, 2012, 15:38

From pictures i see that blade is horizontal. This kind of blade will produce lift in opposite direction i.e., along the direction of flow. What ever be the rotational direction lift direction will not change.
Draw a simple velocity diagram flow is from down to up and blade velocity is horizontal, flow is at positive angle of attack. If blade twisted down beyond this angle it would produce the expected lift. But blade is horizontal for this case.
Results seems to be correct.

January 3, 2012, 01:36		#3
teguhtf Senior Member teguh hady Join Date: Aug 2009 Location: Saga, Japan Posts: 222 Rep Power: 18	Thank's for replying I'm sorry, i have checked it to the literature. My simulation is right. . But now, my problem is on the blade. I have read that axial flow fan concept is the same as aircraft wing. Aircraft use lift of an airfoil. But, the axial flow fan use reaction force of lift to work (3rd newton law). Based on that, i can conclude that if direction of my flow rate is up, my blade lift must be on the opposite direction (down). In my simulation, my lift is in up direction, so my flow rate must be in down direction. I don't know how to fix that. Thanks a lot. Teguh __________________ Now Or Never!!!

January 3, 2012, 05:56		#7
teguhtf Senior Member teguh hady Join Date: Aug 2009 Location: Saga, Japan Posts: 222 Rep Power: 18	Thank you duri I have done some variation on my simulation i.e. Blade angle 5 deg and 10 deg, inlets and outlet value, and RPM of blades. But the lift is still in up direction. I'm still confused with my velocity triangle because my blades are symmetry. Do you have any reference about it?? Thanks for help Teguh __________________ Now Or Never!!!

January 3, 2012, 06:13		#8
D.B Member DB Join Date: Apr 2011 Posts: 87 Rep Power: 15	Hi, you can check a few things, 1st from your geometry it seems the direction of rotation should be anti-clockwise when seen along -Y to +Y direction and the flow should be from +Y to -Y direction. It seems from your figure that your blades are at a negative angle of attack, is it my error in seeing ? just check it might help you out. __________________ -D.B

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January 3, 2012, 02:58		#4
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 17	In axial fan work supplied should equal to the sum of components of drag and lift in theta direction. To know the lift direction, first construct velocity triangle for the fan blade. This gives the local angle of attack, based on this you can figure out the lift direction for the airfoil section. Mostly lift will on the upper surface (suction side). At negative angle of attacks below zero lift angle of attack it will switch direction. Whether fan or turbine lift and rotation direction can be deduced from geometry itself.

January 3, 2012, 05:15		#5
sunflower New Member Join Date: Oct 2010 Posts: 25 Rep Power: 16	Hi Teguhtf, The first picture in your attachment looks very nice. Would you please tell me how to create such kind of picture? I mean how to show the pathline together with geometry frame with grey color. Thanks. [QUOTE=teguhtf;336943]Dear all, I'm simulating axial flow fan in ventilation case (Exhaust) as my thesis project. I put axial in a duct which is connected to small room. I use 4

January 3, 2012, 05:51		#6
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	use mesh overlay A) display----> scene -----> overlays (make sure it is selected) B) display----> scene -----> display and then set transparency Procedure. 1. display mesh (faces) and then set the transparency as required using step B 2. then apply step A 3. display path lines (make sure grid is not selected) you are done

January 4, 2012, 15:38		#11
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 17	From pictures i see that blade is horizontal. This kind of blade will produce lift in opposite direction i.e., along the direction of flow. What ever be the rotational direction lift direction will not change. Draw a simple velocity diagram flow is from down to up and blade velocity is horizontal, flow is at positive angle of attack. If blade twisted down beyond this angle it would produce the expected lift. But blade is horizontal for this case. Results seems to be correct.