Factors Affecting Measured Axial Compressor Tip Clearance Vortex Circulation

Abstract

The relationship between turbomachinery blade circulation and tip clearance vortex circulation measured experimentally is examined using three-dimensional viscous flow computations. It is shown that the clearance vortex circulation one would measure is dependent on the placement of the fluid contour around which the circulation measurement is taken. Radial transport of vorticity results in the magnitude of the measured clearance vortex circulation generally being less than the blade circulation. For compressors, radial transport of vorticity shed from the blade tip in proximity to the endwall is the principal contributor to the discrepancy between the measured vortex circulation and blade circulation. Further, diffusion of vorticity shed at the blade tip toward the endwall makes it impossible in most practical cases to construct a fluid contour around the vortex that encloses all, and only, the vorticity shed from the blade tip. One should thus not expect agreement between measured tip clearance vortex circulation and circulation around the blade.

Comparative Study of the Performance Improvement of an Axial Compressor with a Micro-Vortex Generator and a Suction Slot

“…Each sub-domain corresponds to a type of loss mechanism according to the causes of the local blockage. The evaluation method of the cascade blockage proposed by Khalid (1995) is adopted to obtain the blockage distribution, which is calculated using the scalar ∇(ρvm).…”

A New Segmented Suction Slot Design Based on the Performance of Compressor Cascade

“…The blockage evaluation method proposed by Khalid [19] was used to obtain the blockage distribution in the Therefore, the gradient magnitude should be obtained from the gradient components of ∇ðρv m Þ on the axial plane in the span and circumferential directions. For a Cartesian coordinate system, this gradient can be expressed as j∇ðρvmÞj x,y .…”

Physical Explanations of Tip Leakage Flow Field in an Axial Compressor Rotor

“…The static pressure contour lines on the casing wall and on the blade tip surface are also shown by the black and blue lines. The streamwise vorticity of the tip leakage vortex core is high in the forward half of the blade passage and decreases in the downstream direction due to diffusion of vorticity, although the streamwise structure keeps in the downstream as shown by the high normalized helicity in Fig 3. However, according to the experimental study by Inoue et al (1986) and the numerical study by Khalid (1995), the total circulation of the tip leakage flow field at a trailing edge plane does not so decrease in the compressor rotor, because the vorticity diffused in the casing wall boundary layer has the same sense of rotation. This phenomenon will be interpreted in terms of vortex-lines in Section 3.3.…”

“…The vortex-lines in the suction surface and the casing wall boundary layer are linked together through the diffusion process of the tip leakage vortex core. The reduction rate of the tip leakage vortex circulation cannot be estimated at the trailing edge plane as it is difficult to distinguish the vortex core region from the casing wall boundary layer (Khalid, 1995). In the case of a compressor, the total circulation of the streamwise vorticity dose not decrease by this diffusion because the relative motion of the casing wall enhances the vorticity in the casing wall boundary layer.…”

“…However, it was confirmed by a numerical simulation for a linear cascade (Kang and Hirsch, 1996) that the relative motion of the endwall influences significantly a location of the tip leakage vortex and secondary flows near the trailing edge. The circulation of the tip leakage vortex at a trailing edge plane is also influenced by the relative motion (Khalid, 1995). How is the influence on the flow structure and loss production in a rotating blade row?…”