tailieunhanh - GasTurbine Engineering HandbookSecond Edition phần 5

là tối thiểu bán kính cảm ứng đầu vào tấm vải liệm. Vì vậy, nó không phải là hiệu quả trong việc giảm số Mach tương đối theo cách này. Prewhirl cưỡng bức xoáy. Loại này được thể hiện như V 1 = r1 Â liên tục. Phân phối prewhirl này cũng được hiển thị trong hình 6-14. V 1 là tối đa ở bán kính cảm ứng đầu vào tấm vải liệm, góp phần giảm số lượng đầu vào Mach tương đối. | Axial-Flow Compressors 313 The losses as mentioned earlier can be further described 1. Disc friction loss. This loss is from skin friction on the discs that house the blades of the compressors. This loss varies with different types of discs. 2. Incidence loss. This loss is caused by the angle of the air and the blade angle not being coincident. The loss is minimum to about an angle of 4 after which the loss increases rapidly. 3. Blade loading and profile loss. This loss is due to the negative velocity gradients in the boundary layer which gives rise to flow separation. 4. Skin friction loss. This loss is from skin friction on the blade surfaces and on the annular walls. 5. Clearance loss. This loss is due to the clearance between the blade tips and the casing. 6. Wake loss. This loss is from the wake produced at the exit of the rotary. 7. Stator profile and skin friction loss. This loss is from skin friction and the attack angle of the flow entering the stator. 8. Exit loss. 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. Stall Analysis 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 used to obtain the frequency spectra. In the first four stages of the compressor no outstanding vibration amplitudes were recorded. A signal was noted at 48A A being the running speed but the amplitude was not high and it did not fluctuate. A measurement at the low-pressure bleed chamber taken from the fourth stage showed similar characteristics. The