Reply to post: Re: It's science!

Flying Scotsman attacked by drone

Martin Gregorie Silver badge

Re: It's science!

Coanda effect applies only if water sticks to the rod.

Nope. Coanda applies wherever there's a shear in a moving, compressible fluid. The water column is dragging air, whose other side is sticking to the rod, past it. The shear occurring in that air layer as its dragged past the rod is what deflects the water. Air is a compressible fluid, so the combination of viscosity and shear reduces the pressure in the air mass as it passes the rod and, as a result, the water is deflected toward the low pressure region. If the water stream touches the rod then all the shear is in the water stream. Since water is more viscous than air, of course the deflection is much greater.

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