Uneven Airflow of a Fan: Explained

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SUMMARY

The discussion focuses on the uneven airflow of a house fan, specifically noting that airflow measurements taken 6 inches away from the fan revealed significantly stronger airflow on the left side (A) compared to the right side (C). The fan's rotational symmetry contributes to this phenomenon, as the airflow creates a vortex that is not uniformly distributed. Measurement techniques, including the positioning of the airflow meter and the fan's distance from surfaces, are critical factors influencing the observed airflow discrepancies.

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  • Knowledge of fan design principles, including rotational symmetry
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Why is the airflow of a fan (a regular house fan for instance) stronger on one side than it is the other? I think it has something to do with the fact that the airflow is a vortex, but I don't understand how this creates uneven airflow.

Thanks
 
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I don't understand the question. How is it stronger on one side?
 
russ_watters said:
I don't understand the question. How is it stronger on one side?

Let's say you are looking at the fan. We initially tested the airflow meter about 6 inches away from the fan, and centered (B). Then we measured a 45 degree angle from the fan at the 6 inch distance again, and took measurements again, both to the right and to the left. This would put the air flow meter roughly perpendicular to the meat of the fan blades. The air flow readings indicated that there was significantly more airflow from the left side of the fan (A) than there was from the right side of the fan (C).

Fan
/ | \
/ | \
/ | \
A B C
 
More data. What direction is the fan rotating in? CW or CCW?

The fan is rotationally symmetrical, not reflection symmetrical, so its vortex will be too. Are your measurment points horizontally level with the centre of the fan? If you were measuring a little high, you'd get a different result for the 'up' side of the fan than the 'down' side.

Was the fan physically distant from whatever it was sitting on? I can imagine a loss in air flow on one side but not the other if you were using a small fan sitting on a desk.
 

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