Hydrodynamics studies the movement of liquids.
Hydrodynamics is the area of physics that is dedicated to analyzing the movement of fluids . A fluid , meanwhile, is a substance whose particles are joined together by a force of attraction that is weak .
What hydrodynamics studies
Since liquids and gases are fluids, both subjects could be the subject of study by hydrodynamics. However, this scientific branch focuses on the investigation of the characteristics of the movement of incompressible fluids : that is, water and other liquids.
In this way, hydrodynamics takes incompressible liquids (whose density does not change with changes in pressure ) as a starting point. Furthermore, it considers that the flow of liquids occurs in a steady state (with a speed independent of time at any point) and with an energy loss due to viscosity that is negligible.
The origins
"Hydrodynamica" , a work published in 1738 by the Swiss physicist Daniel Bernoulli , is referred to as the pioneering work for the development of hydrodynamics. This scientist, in fact, gives the name to one of the fundamental laws of this field of knowledge.
Bernoulli's principle maintains that, in an ideal fluid flowing through a closed conduit, the energy remains constant throughout the entire journey. As it is an ideal fluid, friction and viscosity are not taken into account.
From this principle derives Torricelli's theorem , which postulates that the speed of a fluid in an open container is equal to that of any body that falls freely into the vacuum from the level of the fluid until it reaches the center of gravity of the opening.
Incompressible fluids are the object of interest of hydrodynamics.
Hydrodynamics and Reynolds number
Another important concept for hydrodynamics is the Reynolds number , a dimensionless number that relates the inertial forces and viscous forces acting in a fluid. Thus it links velocity, viscosity and density in one expression.
When we talk about a dimensionless number, it means that it is not linked to any physical unit that can define it, so it is a pure one. It is used as a quotient or product of quantities that do have units, so that they are simplified. The Reynolds number is a ratio between two terms: convective and viscous.
The notion of flow
Nor can we leave aside the flow , a concept that is used in fluid dynamics to define the amount of fluid that, for each unit of time, circulates in a part of the pipeline (which can be a river, an oil pipeline, a canal, a pipe or a pipe, among other possibilities). It is usually related to volumetric flow , the volume passing through a given surface in a given time.
The variable used in this context is G , since it is also known as expense . This is one of the most important magnitudes within the field of hydrodynamics. With respect to its equation, to solve the cost, the ratio must be carried out between the volume of liquid (which is expressed as ΔV, the first symbol being the Greek letter "delta", which refers to a change in the value over time) and the unit of time (Δt): G = ΔV / Δt .
According to the International System of Units , flow is expressed in cubic meters per second. This means that ΔV must be indicated in cubic meters, and Δt, in seconds. Depending on the values that we have at our disposal, after solving this equation we can obtain one of the following two possible data : how long it takes to pass a given volume of liquid; how much of said liquid can pass in a given interval.