Ducted fan intake

**JD88** · Nov15-09, 11:44 PM

Would the performance of a ducted fan be negatively affected by the presence of a surface flush with the intake of the fan?

**russ_watters** · Nov16-09, 12:49 AM

Um...it sounds like you are asking if the performance of a ducted fan would be negatively affected by blocking the inlet. How could it not be?

**minger** · Nov16-09, 08:07 AM

Sure any discontinuities or irregularities will negatively affect the performance. What do you mean exactly be surface flush? Like two surfaces not sharing the same centerline?

**JD88** · Nov16-09, 08:14 AM

I have a surface with a hole cut in it that is the diameter of the fan. The fan is then placed in this hole so that the surface and the inlet of the fan are in the same plane.

**Q_Goest** · Nov16-09, 11:54 AM

Yes, the performance (flow and/or pressure) will be negatively affected. A well rounded entrance is best to provide a smooth flow of air into a fan. A quantitative difference would need to look at the fan's actual operating point. Do you need to actually determine the operating point of the fan or are you just asking qualitatively if the fan's performance will be adversely affected?

**JD88** · Nov16-09, 05:26 PM

Just qualitatively.

My fan is currently hooked up to a force balance to measure thrust, and I was concerned that this situation may not accurately reflect how the fan will perform.

**FredGarvin** · Nov16-09, 08:54 PM

It will allow it to perform just not as well as it could. This is why there is a lot of design and analysis work that goes into things like nacelles and inlets on aircraft.