Compressors axial flow

Efficiencies are 8-10% higher than those of comparable centrifugal compressors. 

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Mechanical Impulse The principle of mechanical impulse when applied to fluids is usually combined with one of the other means of imparting motion. As mentioned earher, this is the case in axial-flow compressors and pumps. The turbine or regenerative-type pump is another device which functions partially oy mechanical impulse. 

To be able to decide which type of compressor would best fit the job, we should first divide the compressors into three main categories positive displacement, centrifugaf and axial flow In general terms, positive displacement compressors are used for high pressure and low flow characteristics centrifugal compressors are used for medium to high pressure dehvery and medium flow and axial flow compressors are low pressure and high flow... 

Continuous-flow compressors. a. Centrifugal compressors h. Axial flow compressors... 

Axial Flow Compressors Axial flow compressors are used mainly as compressors for gas turbines. They are also used in the steel industiy as blast furnace blowers and in the chemical industry for large nitric acid plants. Thev are mainly used for apphcations where the head required is low and the flow large. 

The axial flow compressors in aero gas turbines are heavily loaded. The aspecl ratio of the blades, especially the first few stages, can be as high as 4.0, and the effecl of streamhne curvature is substantial. The streamline configuration is a function of the annular passage area, the camber and thickness distribution of the blade, and the flow angles at the inlet and outlet of the blades. The shafts on these units are supported on antifriction bearings (roller or ball bearings). 

Axial-Flow Compressors. An axial-flow eompressor eompresses its working fluid by first aeeelerating the fluid and then diffusing it to obtain a pressure inerease. The fluid is aeeelerated by a row of rotating airfoils or blades (the rotor) and diffused by a row of stationary blades (the stator). The... 

Figure 3-10 shows a similar performance map for an axial-flow compressor. Note the smaller operational flow range for the axial-flow compressor as compared to the centrifugal compressor. Figure 3-11 shows a typical compressor map presented from a slightly different viewpoint. On this map. 

Figure 3-10. Typical flow map for an axial-flow compressor.

The turboprop engine has a power turbine instead of the nozzle as seen in Figure 4-2. The power turbine drives the propeller. The unit shown schematically is a two-shaft unit, this enables the speed of the propeller to be better controlled, as the gasifier turbine can then operate at a nearly constant speed. Similar engines are used in helicopter drive applications and many have axial flow compressors with a last stage as a centrifugal compressor as shown in Figure 1-14. 

Medium-sized gas turbines between 5-50 MW are a combination of aero-derivative and frame type turbines. These gas turbines have axial flow compressors and axial flow turbines. 

As with other types of rotating machinery, an axial compressor can be described by a cylindrical coordinate system. The Z axis is taken as running the length of the compressor shaft, the radius r is measured outward from the shaft, and the angle of rotation 6 is the angle turned by the blades in Figure 7-2. This coordinate system will be used throughout this discussion of axial-flow compressors. 

Figure 7-3. Variation of enthalpy, velocity, and pressure through an axial-flow compressor.

The original work by NACA and NASA is the basis on which most modern axial-flow compressors are designed. Under NACA, a large number of blade profiles were tested. The test data on these blade profiles is published. The cascade data conducted by NACA is the most extensive work of its kind. In most commercial axial-flow compressors NACA 65 series blades are used. These blades are usually specified by notation similar to the following 65-(18) 10. This notation means that the blade has a lift coefficient of 1.8, a profile shape 65, and a thickness/chord ratio of 10%. The lift coefficient can be directly related to the blade camber angle by the following relationship for 65 series blades ... 

Axial-Flow Compressors 283 Laminar-Flow Airfoils... 

The same water tunnel was used for tests to study the effect of casing treatment in axial-flow compressors. In this study, the same Reynolds number and specific speeds were maintained as those experienced in an actual axial-flow compressor. 

The degree of reaction in an axial-flow compressor is defined as the ratio of the change of static head in the rotor to the head generated in the stage... 

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