Question
Question: What is the limit between a perfect fluid and a real fluid?...
What is the limit between a perfect fluid and a real fluid?
Solution
When subjected to shear forces, a fluid exhibits no resistance to shear deformation and will continue to distort. A fluid has no fixed shape and adapts to the form of the container in which it is confined. A shearing force on fluid will cause it to alter its shape. As a result, when shearing forces engage on a fluid, it flows.
Fluids classified into two types:
ideal (or perfect) fluids
real fluids.
Complete step-by-step solution:
The limitations between a perfect fluid and real fluid:
| Limitations | Perfect fluid (ideal fluid) | Real fluid |
|---|---|---|
| Compressible | They are incompressible | They are readily compressible |
| Specific mass | They have a high specific mass | They have a very low specific mass |
| Free surface | Ideal fluid can have a free surface. | The real fluid does not have a free surface |
| Viscosity | A given mass of perfect fluid occupies a definite volume of the container. | They fill the container fully regardless of their mass |
| Flow mode | Laminar mode. | Turbulent mode. |
| Friction | They do not have friction. | They are very flexible with friction. |
Additional information:
Properties of fluid:
Several fundamental features of fluids help us comprehend them better:
Viscosity:
In fluids, it is the ratio of applied shear stress to achieved shear strain rate. The viscosity of a fluid layer provides resistance to its movement.
Pressure:
It is the term used in fluids that correspond to the phrase stress in solids. Both are the ratio of applied force to surface area (on which the force is applied).
Specific gravity:
Fluid specific gravity is defined as the density of a given fluid divided by the density of a reference fluid (generally water).
Note: A perfect or ideal fluid is where only pressure forces exist whether the fluid is at rest or in motion; in an ideal fluid, forces applied on any internal section are perfectly typical to the part even when the fluid is in motion. A perfect fluid is entirely frictionless since there are no tangential forces. In actuality, such a fluid does not exist.