Experimental Study of Boundary Layer Control Through Tip Injection on Straight and Swept Compressor Blades

2005 ◽  
Author(s):  
Bhaskar Roy ◽  
Manish Chouhan ◽  
Kota Venkata Kaudinya
Keyword(s):  
Boundary Layer ◽  
Practical Importance ◽  
Rotor Blades ◽  
Boundary Layer Control ◽  
Additional Parameter ◽  
Stall Margin ◽  
Injection Angle ◽  
Operating Range ◽  
Tip Injection ◽  
Layer Control

Recent research on the use of three dimensional blade designs incorporating sweep and casing boundary layer control through tip injection have shown improved efficiency, stage loading and stable operating range Both methods are known to stabilize the flow at the tip trailing edge (Stall Inception Point) of the compressor blade under lower than design mass flow conditions and improve the compressor performance. This study, performed on a low speed axial flow fan, is aimed to improve the understanding and to assess the improved stall margin due to tip injection on swept and straight blades. Injection through flush mounted nozzles on the casing before the rotor blades is of practical importance because of the non-interference of the nozzles with the main flow. Benefits in terms of efficiency and operating range have already been established and swept blades were found to perform better than the baseline straight blades. The injection mechanism involves 12 symmetrically located flush mounted nozzles before the rotor blades in the casing. The number of injection nozzles used is an additional parameter of the study. Although there are manufacturing limitations in the air injection angle, two injection angles (10° and 30°) have been tried. The improvement in stall margin is more pronounced in the straight blades than in the swept blades and the 10° injection angle with 6 active injection holes gives the best performance in comparison to other combinations.

Active Flow Control in a Single-Stage Axial Compressor Using Tip Injection and Endwall Boundary Layer Removal

2008 ◽  
Author(s):  
B. Dobrzynski ◽  
H. Saathoff ◽  
G. Kosyna ◽  
C. Clemen ◽  
V. Gu¨mmer
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Active Flow Control ◽  
Stall Margin ◽  
Operating Range ◽  
Oil Flow ◽  
Tip Injection ◽  
Active Flow ◽  
The Impact ◽  
Stage Efficiency

Different active flow control techniques have been investigated in a 1.5-stage axial-flow compressor. Looking at a low-speed single-stage environment, many researchers have shown that highly loaded compressors are tip critical, showing stall inception caused by short length scale disturbances (spikes). It has been shown by several authors that these disturbances are related to the spillage of endwall flow ahead of the blading (spill forward). For the present work, different tip injection configurations were investigated in order to stabilize the near casing flow, increasing the operating range of the compressor. Stall margin improvement and the impact on stage efficiency are compared and discussed. Oil flow pictures of the casing wall above the rotor and of the stator blades as well as traverse data from pneumatic 5-hole probes show the impact of flow control on rotor and stator performance. Another method of energizing the casing wall boundary layer is the removal of low energy fluid by a circumferential slot above the rotor, which was also studied experimentally. Again, the impact on compressor operating range and efficiency, as well as flow field information collected by oil flow visualization and traverse data are discussed. Comparing the different flow control techniques, it is shown that increasing stall margin is not directly linked to stage efficiency. As described in various publications, discrete tip injection is a very powerful technique as far as range extension is concerned, but it also has substantial drawbacks such as the circumferential inhomogeneity of the rotor exit flow. These inhomogeneities may result in poor stator performance, overall resulting in a drop of stage efficiency. This problem does not occur if circumferential boundary layer removal above the rotor is used. This method however shows much less potential for increasing the operating range.

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