FAQ About Fluid Mechanics

Fluids are substances that can flow and take the shape of the container in which they are placed. Fluids cannot resist tangential or shear forces in equilibrium. All fluids have some compressibility and show little resistance to deformation.

• Viscous and Inviscous Flows
• Internal and External Flows
• Compressible and Incompressible Streams
• Laminar and Turbulent Flows
• Natural and Forced Flows
• Steady and Unsteady Flows

A frictional force occurs between two fluid layers moving at different speeds. The slow moving flow layer tries to slow down the faster moving flow layer. This internal resistance to flow is called viscosity. Viscosity occurs in liquids due to the intermolecular force of attraction, while in gases it occurs due to the collisions of molecules.

Flows in which friction effects are significant are called viscous flows. In flow regions, the greatest viscosity occurs at or near the surface of the solid. Far from the surface, the viscosity is negligibly small. Flows where the viscosity is so low that it is negligible are called inviscous flows.

Internal flows occur in an area completely delimited by solid surfaces. If a fluid flows over a plate, around a ball or a wire, with no boundaries, it is external flow.

Compressibility is an important parameter for the classification of flows. If, during flow, the density of the fluid remains constant in all regions, the flow is classified as incompressible. If a large change in the density of the fluid occurs during flow, the flow is considered compressible.

Flows are sometimes turbulent, irregular, or regular, depending on the geometry and type of flow.

If the flow is regular without any turbulence, it is called laminar flow.

Turbulent flow is also called turbulent flow, which is often seen in high velocity flows. For example, high velocity flow of low viscosity fluids such as air is called turbulent flow.

Flows that occur naturally, such as the rise of the heated fluid and the descent of the cold fluid, are called natural flows. If there is an unnatural effect that initiates the flow movement, this flow is called forced flow.

Steady flow types mean that there is no change in the characteristics of the flow in a given area over a period of time. If the properties of the flow change over a period of time, this flow is called unsteady flow.

Fluid mechanics is divided into three parts.

1. Hydrostatic: Examines the state of stationary fluids
2. Kinematics: It deals only with the velocity and streamlines of the fluid in motion.
3. Hydrodynamics: It examines the relations between the velocity and acceleration of the fluid in motion and the forces acting on the fluid.

Fluids are divided into Newtonian and non-Newtonian fluids. A Newtonian fluid is a fluid in which the relationship between the applied shear stress and the resulting deformation rate (shear rate) is linear. So they have constant viscosities at a given temperature.

A term with multiple uses in fluid mechanics and thermodynamics. The first and most well known is the concept of specific heat under constant pressure, and its unit is joule/kg*kelvin. For calorically ideal gases, the enthalpy is equal to the temperature times cp.

Usually centipoise (cP) is used in a hundredth. For example, the viscosity of water is 1.0020 cP at 20°C. 1 poise = 100 centipoise = 1 g cm−1 s−1 = 0.1 Pa·s. 1 centipoise = 0.001 Pa·s.

To summarize briefly, the application areas of fluid mechanics are as follows;

• Natural Flows and Meteorological Events
• Ships
• Air and Space Vehicles
• Power Plants
• Human body
• automobiles
• Wind Turbines
• Pipelines and Plumbing

Although each fluid differs from the others in composition and specific properties, each fluid has some characteristics it shares.

These features can be broadly categorized as follows:

Kinematic properties such as velocity and acceleration.

Thermodynamic properties of fluids such as density, temperature, internal energy, pressure, specific volume and specific gravity.

Physical properties of fluids such as appearance, color and smell.

Intensity

The density of a fluid is its mass per unit volume.

Heat

Temperature or coldness determines the physical state of the fluid.

Pressure

The pressure of a fluid is the force applied per unit area.

Specific Volume

In fluid mechanics, specific volume is the reciprocal of density.

The boundary layer is the thin layer in which the interaction between the solid and the fluid occurs due to fluid viscosity. The reason why it is important in fluid mechanics is that the boundary layer determines the lift and drag in the fin and the flow loss in the in-pipe flow.

The flow regime significantly affects the power required to pump the fluid. The flow of a fluid in a pipe can be laminar or turbulent. The transition from laminar to turbulent flow depends on geometry, surface roughness, flow velocity, surface temperature, and fluid type, among other factors.

The volume of liquid per unit time passing through the selected section of the body through which a liquid flows is called the flow rate. It is abbreviated with the letter Q in physics subjects and is a concept in many formulas.

Flow rate can be defined as the velocity of liquids passing through objects, since it is a kind of velocity calculation.

The connection between the percentage of movement of the valve plug and the percentage of fluid passing through the valve is the valve flow characteristic.

Flow Indicator is an element used to monitor the flow in closed pipe circuits from different directions. Flow indicators can be connected before and after steam traps, monitoring steam leakage, food, medicine, etc. They are used in industries to provide visual control of the fluid.

Continuous losses depend on fluid density and viscosity, pipe diameter and length, pipe inner surface roughness and flow velocity.

The p (kg/m³) in the equation represents the specific gravity of the water. Here m (kg/s), G mass flux (kg/s.m²) G=p v, Q volumetric flow rate (m³/s) Q v A.