Darcy's law is similar to Ohm's law for the current in a conducting medium  is confirmed by experiments in the electrolytic bath Taylor. Lines of equal potential in a conducting fluid can be traced using a probe with an insulated conductor. Consequently, the potential flow around the obstacles can be studied by placing their models, made of an insulator between the plates in a bath of conductive material, to which a certain potential difference. Taylor originally intended to study the flow of air over the surface roughness, manufacturing paraffin terrain model. However, in this case, the analogy is not complete, since it is usually the height of the wind increases and can not be considered for irrotational.
On the rigid boundary of a viscous fluid is placed the condition that the velocity to zero. We can assume that for about small air bubbles in water is irrotational, as the shear stress in the liquid at the interface of the gas is negligible and there is quite applicable boundary condition for inviscid fluid. However, while the surface tension tends to make the surface of the bubble is strictly spherical, impurities present in water creates resistance to movement on its surface. Since, according to the equation the maximum pressure developed ahead.
There is another factor that makes for a viscous fluid near the free surface of a great movement of inviscid fluid, although at this boundary shear stress and no restrictions on the tangential velocity component. That factor is the deformation elements irrotational fluid in movement through curves. In a viscous fluid while there are shear stresses, and the flow on the free surface is different. For example, the flow near the surface of the crater formed LIS flow of a viscous fluid through a hole can not be irrotational and have a speed proportional to k / r, since this would require the shear stresses. Therefore, by reducing the speed of the surface of a secondary currents. In addition, there is a trend, downward on the surface of the funnel in the hole runoff is the same for there near the bottom of the vessel.
Energy dissipation as a result of viscous forces in an incompressible fluid can be seen from the following equation, the mechanisms of the process: Capacity of the surface forces.
