4.
Skin1ri句tionlo，， . This loss is from skin friction on the blade surfaces and on the annular walls.
5.
Clearan句elo，， . This loss is due to the clearance between the blade tips and the casing.
6.
Wakelo，， . This loss is from the wake produced at the exit of the rotary.
7. Stator ro1ile and，kin1ri句tionlo，， . This loss is from skin friction and
the attack angle of the flow entering the stator. ..Exitlo，， . This loss is due to the kinetic energy head leaving the stator.
Figure 7-33 shows the various losses as a function of flow. Note that the compressor is more efficient as the flow nears surge conditions. Figure 7-34 also shows a typical axial-flow compressor map. Note the steepness of the constant speed lines as compared with a centrifugal compressor. The axial-flow compressor has a much smaller operating range than its counterpart in the centrifugal compressor.
StallAnal叩sis of an Axial-Flow Compressor
A typical vibration analyis identified a surge condition in the fifth stage of an axial compressor. A pressure transducer with a voltage output was usedto obtain the frequency spectra. In the first four stages of the compressor， no outstanding vibration amplitudes were recorded. A signal was noted at 4 N (Nbeing the runningspeed)， but the amplitude was nothigh， and it did not fluctuate. A measurement at the low-pressure bleed chamber taken from the fourth stage showed similar characteristics. The compressor high-pressure bleed chamber occurs after the eighth stage. A measurement at this chambershowed a high， fluctuating 4 N signal. As there are 4 blades on the fifth-stage wheel， a problem in the fifth stage was suspected. However， above the fifth stage are blade rows of .6N (2 x 4 N)， so the analysis was not clearcut. It was found that the measurement at the high-pressure bleed chamber
.14 Gas Turbine Engineering Handbook
Figure 7-... Losses in an axial-flow compressor stage.
Figure 7-.4. .erformance map of an axial-flow compressor.
showed only a very small 6N amplitude compared to the high amplitude of the 4 N frequency. Since blade rows of 6 blades were closer to the high-pressurebleedchamber， the expected high signal should have been .6N compared to 4 N under normal operating conditions. This high amplitude of 4 Nindicated that it was the fifth stage that caused thehigh， fluctuatingsignal;thus， a stall condition in that section was probable. Figures7-35，7-36，7-37， and 7-3.show the spectrum at speeds of4100，5400，.000， and.400 rpm. At .400rpm， the second and third harmonics of 4 N were also very predominant.
Next， the fifth-stage pressure was measured. Onceagain， a high amplitude at 4 Nwas found. However， a predominant reading was also observed at 1200 Hz frequency. Figures 7-3. and 7-40 show the largest amplitudes atspeeds of 5.00 and 6.00rpm， respectively.
At the compressor exit， predominate frequencies of 4 N existed up to speeds of 6.00 rpm. At.400rpm， the 4 N and 6N frequencies were of about equal magnitudes.the only signal where the 4 N and .6N frequen-cies were the same. The pressure was measured from a static port in the
Figure 7-.5. High-pressure bleed chamber-..0. rpm.
Figure 7-.6. High-pressure bleed chamber-5.0. rpm. .16 Gas Turbine Engineering Handbook
Figure 7-.7. High-pressure bleed chamber-800. rpm.
Figure 7-.8. High-pressure bleed chamber-..0. rpm.
Figure 7-.9. Fifth-stage bleed pressure-580. rpm.
chamber. All other pressures were measured from the shroud， thus indicat-ing the phenomena occurred at the blade tip. Since the problem was isolatedto the fifth stage， the conclusion was that the stall occurred at the fifth-stage rotor tip. A subsequent inspection confirmed the suspicion when cracks at the blade hubs were noticed.
Bibliograph叩
Boyce， M.P.， ""Transonic Axial-Flow Compressor，"" ASME Paper No. 67-GT-47.
Boyce.M.P.，""Fluid Flow Phenomena in DustyAir，""(Thesis)， University ofOklahoma GraduateCollege，1.6.， p. 1..
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