What is Inviscid and Viscous Flows in Fluid Mechanics?

Fluids constitute a very important aspect of most engineering systems. Hydraulic machines, airplanes, the casting of metals… Engineers and designers must deal with fluid flow in every aspect of engineering. Especially in mechanical engineering, there is a wide variety of applications of fluid flow and fluids. For example in turbomachinery, the distinction between inviscid flow and viscous flow is very clear. 

In this article, you can find brief information about inviscid flow and viscous flow in fluid mechanics.

What is the Viscous Flow?

First of all, we need to understand the viscosity term of fluids. Think about a flowing fluid. In theory, fluids are flowing in a layered fashion. And there is clear friction between these layers which makes the slower layer slow down the faster layer. This internal frictional behavior of fluid flow is called viscosity. So, flow phenomenons that exhibit this kind of behavior are called viscous flow. 

What is the Inviscid Flow?

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We stated that all the fluids have a viscosity to a certain extent. To illustrate and understand the inviscid flow, we need to make imaginary experimentation. 

Think about there are two plates, one plate is stationary and the other one is moving. And there is fluid between these two plates. Because of the no-slip condition, there will be a layer of fluid which stationary on the stationary plate. When we go away from this stationary plate, the fluid layers will move more quickly from the bottom layers. At the moving layer, there is a boundary layer of fluid that moves at the same speed as the plate. We can call this layer an inviscid flow in which viscous effects are negligible. 

These two terms are the approximations in fluid mechanics engineering. As a good engineer, you must have the ability to make approximations and assumptions in the light of this informations. 


To the most basic extent, the general definitions of inviscid and viscous flows can be made like above. 

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