**1. Introduction**

**Fluid Mechanics** is a branch of mechanics, mainly studies the static state and motion state of fluid itself and the interaction and flow rules when the fluid and solid wall have relative motion under the action of various forces.

**2. Basic Assumptions**

1) Continuum hypothesis

2) Mass conservation

3) Momentum theorem

4) Stress tensor

5) Viscosity hypothesis

6) Energy conservation

**3. Branches**

1) Earth fluid mechanics

2) Hydrodynamics

3) Aerodynamics

4) Seepage mechanics

5) Physical - chemical fluid dynamics

6) Multiphase fluid mechanics

7) Plasma dynamics and electromagnetic fluid mechanics

8) Environmental fluid mechanics

9) Biological rheology

In addition, such as from the angle of the fluid force, fluid mechanics can be divided into fluid statics, fluid kinematics, and fluid dynamics; from the different mechanics model of points, fluid mechanics can be divided into ideal fluid dynamics, viscous fluid dynamics, non compressing fluid dynamics, compressible fluid dynamics and non Newtonian fluid mechanics, etc.

**4. Research methods**

1) On site observation

2) Laboratory simulation

3) Theoretical analysis

Establishing "mechanical model", establishing control equations, solving equations, analyze and explain the solution

4) Numerical calculation

The relationship between the four research methods:

When solving the problem of fluid mechanics, the field observation, the laboratory simulation, the theoretical analysis and the numerical calculation are mutually reinforcing. Experiments need theoretical guidance, in order to obtain a regular conclusion from the phenomenon of dispersion, surface and experimental data. On the contrary, theoretical analysis and numerical calculation to rely on field observation and laboratory simulations are given physical pattern or data to establish the flow mechanics model and the mathematical model. Finally, it must depend on the test of these models and models of the degree of perfection. In addition, the actual flow is often complicated (such as turbulence, theoretical analysis and numerical calculation will encounter great mathematical and computational difficulties, not the specific results, only through the field observation and laboratory simulation study.

**5. Research Areas**

Theoretical fluid mechanics, hydrodynamics, gas dynamics, aerodynamics, suspension mechanics, theory of turbulence, viscous fluid mechanics, multiphase fluid mechanics, fluid mechanics, physical chemical fluid mechanics, plasma dynamics, electromagnetic fluid mechanics, non Newtonian fluid force, fluid mechanics of fluid mechanical, rotating and stratified fluid mechanics, radiation fluid mechanics, computational fluid mechanics, experimental fluid mechanics, environmental fluid mechanics, micro fluid mechanics, bio fluid mechanics etc.