Where is the air flow?

[LDB]

Our ceiling fan will be doing a great job with significant air flow and then it's as if a giant invisible baffle was put in place and zero air flows. It's at random intervals and lasts for random variable amounts of time. Then all of a sudden it's like the invisible baffle retracts and the full flow of the air hits you again. I think it's the aliens messing with it. I can't figure out anything to re-position in the room to eliminate it. Anyone experience this with your own fan? What's the solution?

[Matt715]

Mine does the same thing. I just ignore it.

[R.I.D.E.]

Is it reversed blowing towards the ceiling?

[ChewChewTrain]

Is this happening in a room with ALL the windows and doors closed?

And, to cover all possibilities, how often do you ingest psychedelics.

[LDB]

It is not reversed. It is randomly intermittent. The fan will blow a great stream of air on you for a while and then suddenly absolutely zero air flow for a random length of time that's usually in the 1 to 4 minutes range. Then full air flow again.

Yes, it's in the living room which is open to the dining and kitchen as well. The fan is almost above the sofa. The tip of the blade might brush against the front edge if they were on the same plane or you might be able to hold 3 sheets of paper in the gap.

[SteveMak]

I'll offer my SWAG (Scientific Wild-Assed Guess): Airflow is a matter of air density -- higher pressures in one place and lower in other. Airflow also performs like waterflow, in some ways, in that moving air has its own inertia. That's why you can feel air pressure in a breeze, or when you stick your hand out in a car at 60 MPH.

So in your closed room, the airflow from your ceiling fan forms "flows" or currents of air, which have their own inertia, and which also collide with other objects (such as walls, furniture, floor, etc.), lose some of their kinetic energy (motion), and continue to travel... until they run out of meaningful kinetic energy. Envision this as "waves" emanating from your fan, and being projected outwards.

This is where things get interesting. When waves interact, they can create constructive and destructive interference. Constructive interference amplifies the wave (like sound amplitude, or pressure), while destructive interference attenuates or diminishes the wave. If you were thinking purely in terms of sound, there would be louder spots and "dead" spots in your room, depending on the placement of your subwoofer and the nature of your room.

Bringing this back to air flow, air moves MUCH slower than sound. As your fan pushes air, that airflow hits walls and the floor and bounces on an altered trajectory... colliding with air flow moving in a different direction. Due to your room (basically a box with a fan at a specific point), that means the air streams (and/or their turbulence) periodically nullify each other to produce what appears to be no airflow from the fan. Like a car crash, these conflicting airstreams eventually lose the kinetic energy (momentum) and become still again. That's when the fan can finally bite into still air, and start up the airflow motion again.

The cycle starts again: air pressure fronts move around the room, bounce off walls and the floor, collide with each other, all until... destructive interference occurs and builds between conflicting airstreams and the flows slow down to a (near) halt again.

You can test this SWAG by doing any of the following:

• Move the ceiling fan to another position
• Move one of the walls (not likely)
• Place a large inclined surface, such as 4'x8' plywood or drywall sheet, directly beneath the fan. This will cause a HUGE air deflection that will significantly change the airflow pattern.

Any of these items should give you very different results, possibly eliminating the "periodic still air" issue, or altering the period and/or duration in which you experience still air. If they do, then they would suggest that my SWAG is correct.


My idea sounds correct (to me), but who knows if it actually is? :-)

[LDB]

I suspect that is correct. It's just challenging to accept since we sit almost directly beneath the fan. While it obviously isn't, it would seem the shortest and most direct path for the air so that it should always hit us. I think I'll go to Lowe's and buy a small fan, 10" or so, and put on the table beside me. I presume with only about 18-22 inches separation it's airflow will be stronger than any of the interferences and reach me uninterrupted.

[ChewChewTrain]

Air AND water flow behave according to fluid dynamics. Water is just 800x more dense.

I agree with Steve that the flow of air is finding a way to cancel itself.

METHOD ONE
1) Establish baseline by timing how long it takes between incidents.

2) Open ALL the windows in the vicinity.

3) Does that affect the baseline timing? If the problem abates, close one window.

4) After closing one window, if the problem STILL abates, close another window and so on.

METHOD TWO
1) Throw a party and have your guests stand in various areas of the room.

2) Sit directly under the fan. When the air begins to reflow, FART.

3) At 5 second intervals, ask your party guests, "Can you smell that?"

This will help you map the flow of air under the fan.

I just realized it may be unreasonable to ask you to fart on command. In this case, eat a bunch of asparagus before hand, and simply wet your pants when the air flow begins.

[rfruth]

Is it a variable speed fan on some kind of timer ?

[LDB]

It is a 3 speed ceiling fan not on any kind of timer.