What is the meaning of various terms for pressure like: static, dynamic, total, operating, absolute, gauge, etc. in the context of fluid dynamics?
Static pressure is the pressure at any point in the fluid. This pressure is a function of the state of the fluid, which for an ideal gas, is related to the density/volume of the fluid through the ideal gas law. It can be measured using an aneroid, mercury column etc.
The concepts of dynamic and total pressure arise from Bernoulli's equation for incompressible flows. Dynamic pressure is the pressure associated with the motion of the fluid and is directly proportional to density and square of velocity of the fluid. Total or stagnation pressure is defined as the sum of static and dynamic pressure.
Pressure is an absolutely measurable quantity and therefore may be referred to as 'absolute pressure' when the reference point of measurement is equal to zero.
In Fluent, for problems where the variation in pressure is small compared to the mean value of absolute pressure, it is advisable to choose the reference point to be equal to the mean absolute pressure to minimize numerical errors. This reference point is referred as the 'operating pressure' and may be specified in Fluent in the Operating Conditions panel accessed from Define->Operating Conditions.
The difference between absolute pressure and operating pressure is referred to as the 'gauge pressure'. All pressure values reported in Fluent are gauge pressures.