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In this two-part paper results of the periodical unsteady flow field within the third rotor blade row of the four-stage Dresden low-speed research compressor are presented. The main part of the experimental investigations was performed using laser Doppler anemometry. Results of the flow field at several spanwise positions between midspan and rotor blade tip will be discussed. In addition, time-resolving pressure sensors at midspan of the rotor blades provide information about the unsteady profile pressure distribution. In Part II of the paper the flow field in the rotor blade tip region will be discussed. The experimental results reveal a strong periodical interaction of the incoming stator wakes and the rotor blade tip clearance vortices. Consequently, in the rotor frame of reference, the tip clearance vortices are periodical with the stator blade passing frequency. Due to the wakes, the tip clearance vortices are separated into different segments. Along the mean vortex trajectory, these parts can be characterized by alternating patches of higher and lower velocities and flow turning or subsequent counter-rotating vortex pairs. These flow patterns move downstream along the tip clearance vortex path in time. As a result of the wake influence, the orientation and extension of the tip clearance vortices as well as the flow blockage periodically vary in time. [ABSTRACT FROM AUTHOR]

In this two-part paper; results of the periodical unsteady flow field within the third rotor blade row of the four-stage Dresden low-speed research compressor are presented. The main part of the experimental investigations was performed using laser Doppler anemomeiry. Results of the flow field at several spanwise positions between midspan and rotor blade tip will be discussed. In addition, time-resolving pressure sensors at midspan of the rotor blades provide information about the unsteady profile pressure distribution. In Part I of the paper; the flow field at midspan of the rotor blade row will be discussed. Different aspects of the blade row interaction process are considered for the design point and an operating point near the stability limit. The periodical unsteady blade-to-blade velocity field is dominated by the incoming stator wakes, while the potential effect of the stator blades is of minor influence. The inherent vortex structures and the negative jet effect, which is coupled to, the wake appearance, are clearly resolved. Furthermore the time-resolved profile pressure distribution of the rotor blades is discussed. Although the negative jet effect within the rotor blade passage is very pronounced, the rotor blade pressure distribution is nearly independent of the convectively propagating chopped stator wakes. [ABSTRACT FROM AUTHOR]