Chapter 12 - Laser velocimeter measurements of the flow...

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Laser velocimeter measurements of the flow field in the rotor row of a low-speed research turbine. 1 Photograph courtesy of Dr. D. C. Wisler, Director, Aerodynamic Research Laboratory of GE Aircraft Engines. 2
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In previous chapters we often used generic “black boxes” to represent fluid machines such as pumps or turbines. The purpose of this chapter is to understand from a fluid mechanics standpoint how these devices work. Pumps and turbines 1 sometimes called fluid machines 2 occur in a wide variety of con- figurations. In general, pumps add energy to the fluid—they do work on the fluid; turbines extract energy from the fluid—the fluid does work on them. The term “pump” will be used to generically refer to all pumping machines, including pumps , fans , blowers , and compres- sors . Fluid machines can be divided into two main categories: positive displacement ma- chines 1 denoted as the static type 2 and turbomachines 1 denoted as the dynamic type 2 . The ma- jority of this chapter deals with turbomachines. Positive displacement machines force a fluid into or out of a chamber by changing the volume of the chamber. The pressures developed and the work done are a result of essen- tially static forces rather than dynamic effects. Typical examples shown in Fig. 12.1 include the common tire pump used to fill bicycle tires, the human heart, and the gear pump. In these cases the device does work on the fluid 1 the container wall moves against the fluid pressure force on the moving wall 2 . The internal combustion engine in your car is a positive- displacement machine in which the fluid does work on the machine, the opposite of what happens in a pump. In the car engine the piston moves in the direction of the fluid pressure force acting on the piston face during the power stroke. Turbomachines, on the other hand, involve a collection of blades, buckets, flow chan- nels, or passages arranged around an axis of rotation to form a rotor. Rotation of the rotor produces dynamic effects that either add energy to the fluid or remove energy from the fluid. Examples of turbomachine-type pumps include simple window fans, propellers on ships or airplanes, squirrel-cage fans on home furnaces, axial-flow water pumps used in deep wells, and compressors in automobile turbochargers. Examples of turbines include the turbine portion of gas turbine engines on aircraft, steam turbines used to drive generators at electri- cal generation stations, and the small, high-speed air turbines that power dentist drills. 759 12 T urbomachines Turbomachines are dynamic fluid ma- chines that add (for pumps) or extract (for turbines) flow energy. The complete material for Chapter 12 is contained in the E-book only.
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Turbomachines serve in an enormous array of applications in our daily lives and thus play an important role in modern society. These machines can have a high power density 1 large power output per size 2 , relatively few moving parts, and reasonable efficiency.
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This note was uploaded on 04/17/2008 for the course ME 111 taught by Professor Usaxena during the Spring '08 term at San Jose State University .

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Chapter 12 - Laser velocimeter measurements of the flow...

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