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Operating Wisely
Published in Carl Bozzuto, Boiler Operator's Handbook, 2021
The measurement of static pressure, velocity pressure, and total pressure is described using Figure 1-5. The static pressure is the pressure in the fluid measured in a way that is not affected by the flow. Note that the connection to the gauge is perpendicular to the flow. The gauge measuring total pressure is pointed into the flow stream so that the static pressure and the velocity pressure are measured on the gauge. What really happens at that nozzle pointed into the stream is that the moving liquid slams into the connection, converting the velocity to additional static pressure sensed by the gauge. There is no flow of fluid up the connecting tubing to the gauge. The measurement of velocity pressure requires a special gauge that measures the difference between static pressure and total pressure. With that measurement, one can determine the velocity of the fluid independent of the static pressure. A velocity reading in a pipe upstream of a pump, where the pressure is lower, would be the same as that in a pipe downstream of the pump (provided the pipe size is the same).
Natural Flight
Published in Malcolm S. Gordon, Reinhard Blickhan, John O. Dabiri, John J. Videler, Animal Locomotion, 2017
Under the wing, the flow velocity is reduced under the small angle of attack. The concave shape enhances the retardation of the flow because the passage widens beyond the leading edge. Unlike commercial aircraft, many bird wing cross sections have a concave lower profile, in some cases even extremely so. According to Bernoulli’s law the static pressure (perpendicular to the flow) is high underneath the wing where the velocity is low. The static pressure difference under and above the wing contributes to the lifting force. However, reaction forces on the wing caused by changes in flow direction also play a substantial role. The flow anticipates the presence of the wing by partly moving upward in front of the leading edge of the wing: the up-wash. The reaction force on the wing due to the oblique up-wash pushes downward and slightly backward. Above the wing, the flow returns to horizontal over the first half of the wing chord. This change of direction is caused by a downward-directed force; the equal and opposite force on the wing is upward and much bigger than the downward force on the wing due to the up-wash. Over the rear half of the chord the flow goes downward: the net down-wash. The reaction force to this change of direction on the wing provides lifting force on the wing. The boundary layer, close to the wing, is too thin to be visualized in this velocity vector diagram, but it plays an important role. Why is the fluid following the curved upper surface of the wing? The fluid in direct contact with the wing surface has zero velocity with respect to the wing, but the velocity increases away from the surface to reach the free stream velocity. The shear between the slow flowing water close to the surface and the faster flow at some distance away from the surface gives the flow the tendency to bend to the surface. This is known as the Coanda⌣ effect. The tendency to follow the shape of the surface causes the change in direction of the down-wash. The total lift force on the wing (and the accompanying drag force) is due to the combined effects of the shape of the wing in the horizontal flow. The rounded leading edge and the curved shape of the cross section, the angle of attack, the flow velocity, and viscous forces in the boundary layer all contribute to the flow pattern around the wing and hence to the forces generated. The net lifting result is shown by the downward flow directly behind the wing.
CFD simulation analysis of two-dimensional convergent-divergent nozzle
Published in International Journal of Ambient Energy, 2020
R. Ramesh Kumar, Yuvarajan Devarajan
We have calculated the fluid static pressure values are directly proportional to static temperature. The static pressure decreases while the static temperature also decreasing correspondingly. The static temperature increases while Mach number values are decreasing correspondingly. We have checked the static temperature; it could be higher in the throat and divergent.