Principles of Fluid Mechanics Missouri ST（流体力学原理密苏里州科技）.pdfVIP

Min-218 Lecture Notes Principles of Fluid Mechanics 1. BASIC PRINCIPLES OF FLUID MECHANICS Ventilation is the application of the principles of fluid dynamics to the flow of air in underground openings. Airflow is induced from the atmosphere, through the intake opening, underground air- ways, return opening, and back to the atmosphere again by a differential pressure between intake and return openings of the mine. This pressure differential is usually very small, in the order of 2 to 3% in most cases, when compared to the absolute pressure of the system. Therefore, volume and density changes are neglected without serious loss of accuracy or validity. Airflow in mines is also generally treated as steady state, turbulent, and incompressible. However, in situations where the pressure, temperatures, and humidity changes are large and air conditioning processes are in- volved, calculations must incorporate compressibility effect of air. 1.1 Definition of A Fluid A fluid may be defined broadly as a substance which deforms continuously when subjected to shear stress . This fluid can be made to flow if it is acted upon by a source of energy. This can be made clear by assuming the fluid being consisted of layers parallel to each other and letting a force act upon one of the layers in a direction parallel to its plane. This force divided by the area of the layer is called shear stress. As long as this shear stress is applied the layer will continue to move relative to its neighboring layers. If the neighboring layers offer no resistance to the movement of fluid, this fluid is said to be frictionless fluid or ideal fluid. (Practically speaking, ideal fluids do not exist in nature, but in many practical problems the resistance is either small or is not important, therefore can be ignored.) A fluid is always a continuous medium