Question

What do you mean by viscous drag?

Answer 1

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluidresistance, another type of friction or fluidfriction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid.

It is the total drag which is caused by viscous effects

D=Df+DpD=Df+Dp

and

DD= Total drag due to viscous effect

DfDf= Drag due to skin friction

DpDp= Drag due to seperation (pressure drag)