9.6 PRESSURE MEASUREMENTS IN MOVING FLUIDS
Pressure measurements in moving fluids warrant special consideration. Consider the flow over the bluff body shown in Figure 9.17. Assume that the upstream flow is uniform and steady with negligible losses. Along streamline A, the upstream flow moves with a velocity U1, such as at point 1. As the flow approaches point 2, it must slow down and finally stop at the front end of the body. Above streamline A, flow moves over the top of the bluff body, and below streamline A, flow moves under the body. Point 2 is known as the stagnation point and streamline A the stagnation streamline for this flow. Along streamline B, the velocity at point 3 is U3 and because the upstream flow is considered to be uniform it follows that U1=U3. As the flow along B approaches the body, it is deflected around the body. From the conservation of mass principles, U4 > U3. Application of conservation of energy between points 1 and 2 and between 3 and 4 yields