Air Jet Fluid Mechanics Experiment

[Rawlins]

Hi all,

Recently did a lab experiment where we had a nozzle pointing vertically upwards at a flat plate normal to the direction of the flow of air.

The plate had a spring gauge on it so that the force of the air on the plate could be measured. The plate was moved to various distances above the air nozzle and it was found that the force remained constant with distance from the nozzle.

However, at very small distances, the force on the plate reduced dramatically.

My question is: Why would the force on the plate remain constant with distance from the nozzle apart from at very small distances?

Thanks.

 

[NTW]

It's just a hunch, but perhaps that's happening because, at very low distances nozzle-plate, there is an intensive radial flow of the air across the bottom of the plate, causing a local drop in air pressure. Hence, the plate is pushed downwards, that force countering the dynamic action of the jet impinging on the plate.

 

[NascentOxygen]

Hi Rawlins. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

If NTW has addressed the question you're asking, then for an everyday example try filling a plastic bucket using your garden hose. You'll find that if you push the nozzle close to the base of the bucket, the hose experiences an attraction towards the bucket, in contrast to what happens at other placements of the hose into the bucket as it fills.