Hello:(adsbygoogle = window.adsbygoogle || []).push({});

Need some help here.

I am trying to Calculate the viscous drag for a body traveling through water at given velocity and wetted surface area. At this time I am not trying to calculate the pressure drag or wave drag.

Basically what I want to know is how many newtons of force are absorbed by the viscous drag only.

I know the basic equation is

Rf = 0.5v^2s , where Rf is the viscous drag, v is velocity and s is the wetted surface area.

What I don't understand is how much force does Rf represent? Is it in Newtons?

Also, is the Rf related to the Coefficient of drag (Cf)? I know the Cf is pressure drag related to the shape of the object, for example about 0.295 for a bullet shaped object. Can you use the Rf in equations that call for the Cf?

Is the Rf related to the Re (Reynolds number)? How do you use the Reynolds number to help calculate the viscous drag losses on a surface area?

I am also confused because the equation Rf = 0.5v^2s does not take into account the temperature of the water. Viscosity varies alot with temperature.

Any help appreciated. To make the math simpler, assume fresh water with a density of 1.0.

Dan

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# Calculating viscous drag in water

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