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-   -   Axial fan Efficiency Goals calculation? (https://www.cfd-online.com/Forums/floefd-floworks-flotherm/111608-axial-fan-efficiency-goals-calculation.html)

 Sanghyun - PARK January 10, 2013 19:16

Axial fan Efficiency Goals calculation?

1 Attachment(s)
Hi~
I check the efficiency of the axial flow fan.

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Example Roating Impeller.

Goals -> Equation -> Pressure drop
={SG Av Static Pressure 1}-{SG Bulk Av Static Pressure 1}

Goals -> Equation -> Efficiency
={Pressure Drop}*{Environment Pressure 1:Volume flow rate normal to face:1.500e+000}/{Rotating Region 1:Angular velocity:3.665e+002}/{SG Torque (Z) 1}
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Copy Top Examples of axial fans.
However, efficiency is a mess.
How to Set Goals for efficiency axial flow fans need to see?

< Unit >
pressure - Pascal
Volume Flow rate - m³/s
Torque - N.m
Efficiency - % [no unit]

Please explain the situation in more detail goals.

http://www.cfd-online.com/Forums/att...1&d=1357858952

 Boris_M February 18, 2013 12:20

Hi Sanghyun,

the best way is to do it as it is done in the tutorial "Rotating Impeller" that comes with the software.
Please take care of your boundary condition, use volume or mass flow rate for the inlet and pressure for the outlet. And ideally naming the boundary conditions or goals correctly if you post here as I have no idea of where surface goals are put and surface goal static pressure 1 is not helping to identify your problem from the text. Also a boundary condition in your equation goal named "Environment pressure 1" but a flow rate beeing specified can confuse.

Also check for your angular velocity units. The whole equation goal only calculated with the values, not the units so the units should match already or you would have to include conversion factors in the equation.

In general rotating region calculations can fluctuate in the beginning for a while until they become stable. Check the inflow and outflow volume flows if the sign is correct. They can switch directions in the beginning and converge towards later iterations only.

Boris

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