Angled Vents

[MAHLY361]

When inputting a volume flow rate and then adding horizontal or vertical components to the louver option, does the volume flow rate have to change?

For instance, if with no louver a 3m3/s gives you a certain thrust based on the area. If you use the same flow rate but add a directional component, would the thrust change and therefore you have to change the volume flow rate value to maintain the same thrust or it’s unaffected as it’s not a velocity component?

[drjfloyd]

I don't think that the tangential will effect the thrust. You may want to make a simple test case where you have a fan with varied angle and see if you feel the thrust is impacted.

[Er9y714]

I do not agree. With tangential component the velocity changes while the volume flow rate remains the same. Since the velocity changes, the thrust changes.

The case below has two fans, each same outlet flow rate. It does not prove the thrust difference as it is but the velocity difference is evident.

 
&MESH ID='Mesh01-01', IJK=20,21,14, XB=-1.8,2.2,-1.6,2.6,-0.8,2.0/
&MESH ID='Mesh01-02', IJK=20,21,14, XB=-1.8,2.2,2.6,6.8,-0.8,2.0/
&MESH ID='Mesh01-03', IJK=20,21,14, XB=2.2,6.2,-1.6,2.6,-0.8,2.0/
&MESH ID='Mesh01-04', IJK=20,21,14, XB=2.2,6.2,2.6,6.8,-0.8,2.0/
&MESH ID='Mesh01-05', IJK=20,21,14, XB=8.2,12.2,-1.6,2.6,-0.8,2.0/
&MESH ID='Mesh01-06', IJK=20,21,14, XB=8.2,12.2,2.6,6.8,-0.8,2.0/
&MESH ID='Mesh01-07', IJK=20,21,14, XB=12.2,16.2,-1.6,2.6,-0.8,2.0/
&MESH ID='Mesh01-08', IJK=20,21,14, XB=12.2,16.2,2.6,6.8,-0.8,2.0/

&DEVC ID='VolFlow', QUANTITY='NORMAL VELOCITY', SPATIAL_STATISTIC='SURFACE INTEGRAL', XB=0.0,0.8,1.0,1.0,1.0,1.6/
&DEVC ID='VolFlow_tangent', QUANTITY='NORMAL VELOCITY', SPATIAL_STATISTIC='SURFACE INTEGRAL', XB=10.0,10.8,1.0,1.0,1.0,1.6/
 
 

&OBST ID='Obstruction', XB=0.0,0.8,0.0,1.0,1.0,1.6, / 
&OBST ID='Obstruction', XB=10.0,10.8,0.0,1.0,1.0,1.6, / 

&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=6.2,6.2,-1.6,6.8,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=-1.8,-1.8,-1.6,6.8,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=-1.8,6.2,6.8,6.8,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=-1.8,6.2,-1.6,-1.6,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [ZMAX]', SURF_ID='OPEN', XB=-1.8,6.2,-1.6,6.8,2.0,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [ZMIN]', SURF_ID='OPEN', XB=-1.8,6.2,-1.6,6.8,-0.8,-0.8/ 
&VENT ID='Jet Fan Inlet', SURF_ID='HVAC', XB=0.0,0.8,0.0,0.6,1.0,1.0/ 
&VENT ID='Jet Fan Outlet', SURF_ID='HVAC', XB=0.0,0.8,1.0,1.0,1.0,1.6/ 
&VENT ID='Mesh Vent: Mesh01 [XMAX]01', SURF_ID='OPEN', XB=16.2,16.2,-1.6,6.8,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [XMIN]01', SURF_ID='OPEN', XB=8.2,8.2,-1.6,6.8,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [YMAX]01', SURF_ID='OPEN', XB=8.2,16.2,6.8,6.8,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [YMIN]01', SURF_ID='OPEN', XB=8.2,16.2,-1.6,-1.6,-0.8,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [ZMAX]01', SURF_ID='OPEN', XB=8.2,16.2,-1.6,6.8,2.0,2.0/ 
&VENT ID='Mesh Vent: Mesh01 [ZMIN]01', SURF_ID='OPEN', XB=8.2,16.2,-1.6,6.8,-0.8,-0.8/ 
&VENT ID='Jet Fan Inlet01', SURF_ID='HVAC', XB=10.0,10.8,0.0,0.6,1.0,1.0/ 
&VENT ID='Jet Fan Outlet01', SURF_ID='HVAC', XB=10.0,10.8,1.0,1.0,1.0,1.6, UVW=1.0,1.0,0.0/ 

&HVAC ID='Jet Fan Outlet', TYPE_ID='NODE', DUCT_ID='Jet Fan Duct', VENT_ID='Jet Fan Outlet'/
&HVAC ID='Jet Fan Inlet', TYPE_ID='NODE', DUCT_ID='Jet Fan Duct', VENT_ID='Jet Fan Inlet'/
&HVAC ID='Jet Fan Duct', TYPE_ID='DUCT', AREA=0.25, PERIMETER=2.0, FAN_ID='Jet Fan 1', NODE_ID='Jet Fan Inlet','Jet Fan Outlet', ROUGHNESS=1.0E-3, LENGTH=0.8/
&HVAC ID='Jet Fan Outlet01', TYPE_ID='NODE', DUCT_ID='Jet Fan Duct01', VENT_ID='Jet Fan Outlet01'/
&HVAC ID='Jet Fan Inlet01', TYPE_ID='NODE', DUCT_ID='Jet Fan Duct01', VENT_ID='Jet Fan Inlet01'/
&HVAC ID='Jet Fan Duct01', TYPE_ID='DUCT', AREA=0.25, PERIMETER=2.0, FAN_ID='Jet Fan 1', NODE_ID='Jet Fan Inlet01','Jet Fan Outlet01', ROUGHNESS=1.0E-3, LENGTH=0.8/
&HVAC ID='Jet Fan 1', TYPE_ID='FAN', TAU_FAN=-0.1, VOLUME_FLOW=3.0/

&SLCF QUANTITY='VELOCITY', ID='Slice', PBZ=1.384782/


&TAIL /

[elangsz]

Any update on this issue? I was modeling a jet fan and by adding a louver with a certain direction, the thrust n speed profile changes

[Er9y714]

I do not agree that this is an issue on input side but rather is confusing in practice. If we breakdown the setup:

Thrust of a fan = mass * velocity. When a louvre angle is set for the VENT, the mass flow and volume flow rate remains the same but the velocity increases at the outlet. Since the velocity increases, the thrust increases.

Therefore to get the same thrust, volume flow rate setting (e.g. VOLUME_FLOW) should be decreased.

[drjfloyd]

We recently added the ability to specify HVAC for GEOM. This may be a route to addressing this. If you install the latest test release there is an HVAC_geom.fds in Verification/HVAC that is representative of a simple jet fan like setup.