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Flow structure of the tip clearance vortex in an axial compressors blade row

Flow structure of the tip clearance vortex in an axial compressors blade row

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Article
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The understanding of the tip clearance flow in axial compressors is a key issue for developing new compressors with enhanced efficiency and reduced noise for instance. However, necessary flow measurements in the blade tip region and within the tip clearance are challenging due to the small gap width. The application of a novel optical measurement t...

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Context 1
... flow field in the tip region of cantilevered stator vane rows and rotor blade rows is dominated by the tip clearance vortex (TCV), which is illustrated in Fig. 1. The pressure difference of the blade drives a balancing out clearance flow through this gap from the pressure side (PS) toward the suction side (SS). When the jetlike tip leakage flow enters the next blade passage, it inter- acts with the main flow and other secondary flow phenomena such as the passage vortex and rolls up into a ...
Context 2
... Steady State Profile Pressure Distribution. The conven- tional measuring techniques data is completed by the profile pres- sure distributions shown in Fig. 10. Here the vanes surface pressure is referred to the inlet plane measurements. The typical characteristic for highly loaded profiles due to high incidences was found at midspan. The highest loaded blade area is the first 10% of chord. From there, the decreasing pressure gradient along the SS indicates separated flow caused by the large ...
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... toward midspan at 0.94h does not show this clearly altered distribution compared to that at mid- span. From these data, the estimated radial dimension of the TCV interaction up to 0.9h from the wake measurements behind the cascade cannot be verified inside the passage. The merged velocity mean values after a coordinate transform are shown in Fig. 11. The velocity z-component c z is color coded. It clearly indicates that c z is directed upward into the gap at the PS and downward to the passage at the SS. Due to the uprolling TCV, the flow is also turned upward at the rear part of the SS. De- spite the high incidence of the inflow, the cascade flow continues along the passage formed ...
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... This applies notably at the PS while the forming TCV deviates the SS flow. The measured outflow angle a; 2 is approximately 75 deg at the PS and decreases to minimum 35 deg at the SS. This is in very good agreement with the results of the 5HP measurements presented in Sec. 3.1 (see Fig. 6). With assistance of the FM-DGV measurements (see Fig. 11) the dimensions of the TCV inside the clearance can be estimated by negative values of c z . The spanwise massflow at SS is caused by the uprolling leakage jet. In axial directions the origin seems to be at 0.05l-0.1l and the end of the vortex core at 0.9l. Despite of the high incidence, the pitchwise position is near the SS with the ...
Context 5
... to Eq. (3), the measurement uncertainty is estimated to 0.6 m/s. Comparing with the results in Fig. 11, the estimated value is smaller than the measured velocity standard deviation, which is due to the flow ...
Context 6
... an example, the PSD of the velocity from two positions of the first velocity component are presented in Fig. 13. The first position at x ¼ 0.56l x , y ¼ 0.526t is located in the center of the tip clearance, whereas the second position at x ¼ 0.56l x , y ¼ 0.738t is at the tail of the TCV. From Eq. (3), the noise power spectral Fig. 13(b) faster flow oscillations up to about 500 Hz occur. Generally, a low-pass char- acteristic is apparent in the ...
Context 7
... an example, the PSD of the velocity from two positions of the first velocity component are presented in Fig. 13. The first position at x ¼ 0.56l x , y ¼ 0.526t is located in the center of the tip clearance, whereas the second position at x ¼ 0.56l x , y ¼ 0.738t is at the tail of the TCV. From Eq. (3), the noise power spectral Fig. 13(b) faster flow oscillations up to about 500 Hz occur. Generally, a low-pass char- acteristic is apparent in the spectra near the TCV, which means the oscillation amplitude is decreasing with increasing frequency. A dominating mode occurring permanently in subsequent spectra could not be ...

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Citations

... Regarding planar methods, in particular particle image velocimetry (PIV) was successfully applied in numerous studies, ranging from the characterization of stator passages and wakes (Bryanston-Cross et al. 1992;Woisetschläger et al. 2003) to applications in rotating machinery (Wernet 2000;Voges et al. 2012). As an alternative approach to PIV, Doppler global velocimetry with frequency modulation (FM-DGV) was applied on a transonic cascade (Fischer et al. 2012) as well as a rotating turbine stage (Fischer et al. 2013). ...
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... Regarding planar laser-optical techniques, in particular PIV and, to a lesser extent, DGV were successfully applied to turbomachinery flows [4][5][6][7][8][9]. Despite their general ability to deliver timeresolved three-component velocity fields in turbomachinery environments, both PIV and DGV suffer from their susceptibility to laser scattering from surfaces, so that affected image areas have to be masked and thus cannot provide data in these areas [6,7,9]. ...
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