II.Measuring fluid pressure Fig 2 shows the schematic of measuring pressure of flowing fluid.Measured pressure p in Fig 2-(1)and 2-(2)is called static pressure,while p in Fig 2-(3)is called total pressure which follows p'=p+(1/2)pv Usually the pressure Ap measured in Fig 2-(4)is called dynamical pressure,which follows Ap=p-p=(1/2)pv. Derived from Bernoulli equation,speed of fluid can be written as: Ap (4) Experimental instrument will be put in wind tunnel.Thus pin equations refers to air density inside tunnel.Under standard air status,the density of dry air is p=1.293 kg/m.In equations,p is the dynamical pressure measured by pressure sensor,while v is wind speed at the position where the sensor is. 而行司 3 4) Figure 2 III.Some knowledges of aerophysics Fig 3 shows the cross section of wing of an air plane and the air flow line around it.As you can see on figure,a region of air with high fluid flow and low pressure will be formed above the wing,while air below wing remains the same status as surrounding atomsphere.So wings not only get resistent force Fw,which holds opposite direction as air plane motion,during a flight,but also get Figure 3 an upward force Fa which is perpendicular to motion.With fixed speed of plane, magnitudes of these two forces depend on a(angle of flying direction over horizontal line). 1414 II. Measuring fluid pressure Fig 2 shows the schematic of measuring pressure of flowing fluid. Measured pressure p in Fig 2-(1) and 2-(2) is called static pressure, while p’ in Fig 2-(3) is called total pressure which follows p’=p+(1/2)  . Usually the pressure p measured in Fig 2-(4) is called dynamical pressure, which follows p=p’ -p=(1/2). Derived from Bernoulli equation, speed of fluid can be written as:  p v = （4） Experimental instrument will be put in wind tunnel. Thus  in equations refers to air density inside tunnel. Under standard air status, the density of dry air is = kg/m3 . In equations, p is the dynamical pressure measured by pressure sensor, while  is wind speed at the position where the sensor is. III. Some knowledges of aerophysics Fig 3 shows the cross section of wing of an air plane and the air flow line around it. As you can see on figure, a region of air with high fluid flow and low pressure will be formed above the wing, while air below wing remains the same status as surrounding atomsphere. So wings not only get resistent force FW, which holds opposite direction as air plane motion, during a flight, but also get an upward force Fa which is perpendicular to motion. With fixed speed of plane, magnitudes of these two forces depend on (angle of flying direction over horizontal line). p p P' （1） (2) (3) (4) Figure 2 a Fa Fw Figure 3