This paper describes the results on an experimental investigation of rotating stall flow inside a single stage axial flow compressor. Tests were carried out in two steps. First, measurements were taken to investigate the transition process into rotating stall. The compressor starts into rotating stall via the “modal route” with a single rotating stall cell. Further throttling yields to a two-cell shape followed by a significant outlet pressure drop. Both transition processes are discussed in detail. Results from the Moore-Greitzer theory are compared with measured data.
In a second step measurements were taken to determine the three-dimensional unsteady structure of a full developed rotating-stall cell. Based on unsteady total pressure and threedimensional hot-wire data, the structure of a rotating stall cell could be resolved in detail upstream and downstream the rotor. A typical part-span stall was found. By inserting the measured data into the Euler-equations convective and unsteady effects on the pressure fluctuations can be isolated. A dependence between the radial flow inside the stall cell and the unsteady flow accelerations was found.
A measuring technique based on multisensor hot-wire anemometry has been developed to determine the unsteady three-dimensional velocity vector and the structure of turbulent flows. It then has been applied to the passage and the exit flow of an annular compressor cascade, which is periodically disturbed by the wakes of a cylinder rotor, located about 50 percent of blade chord upstream. In Part I of this paper the decay of the rotor wakes has been described first without stator and secondly through a stator passage. The time-dependent turbulent flow field downstream of this stator is discussed in Part II of this paper. The rotor wakes have a major influence on the development of three-dimensional separated regions inside the compressor cascade, and this interaction will be addressed in both parts of the paper.
This paper describes the results on an experimental investigation of rotating stall flow inside a single-stage axial flow compressor. Tests were carried out in two steps. First, measurements were taken to investigate the transition process into rotating stall. The compressor starts into rotating stall via the “modal route” with a single rotating stall cell. Further throttling yields to a two-cell shape followed by a significant outlet pressure drop. Both transition processes are discussed in detail. Results from the Moore–Greitzer theory are compared with measured data. In a second step, measurements were taken to determine the three-dimensional unsteady structure of a fully developed rotating-stall cell. Based on unsteady total pressure and three-dimensional hot-wire data, the structure of a rotating stall cell could be resolved in detail upstream and downstream of the rotor. A typical part-span stall was found. By inserting the measured data into the Euler equations, convective and unsteady effects on the pressure fluctuations can be isolated. A dependence between the radial flow inside the stall cell and the unsteady flow accelerations was found.
A measuring technique based on multisensor hot-wire anemometry has been developed to determine the unsteady three-dimensional velocity vector and the structure of turbulent flows. It then has been applied to the passage and the exit flow of an annular compressor cascade, which is periodically disturbed by the wakes of a cylinder rotor, located about 50 percent of blade chord upstream. In part I of this paper the decay of the rotor wakes will be described first without stator and secondly through a stator passage. The time-dependent turbulent flow field downstream of this stator is discussed in Part II. The rotor wakes have a major influence on the development of three-dimensional separated regions inside the compressor cascade, and this interaction will be addressed in both parts of this paper. NOMENCLATURE a coefficients for sensor calibration c velocity i incidence angle to the stator I mixing length h calibration coefficient for the hot -wire sensor k calibration coefficient for the hot -wire sensor L dimension of polynomial fit M number of points per time window dimension of polynomial fit N number of time window dimension of polynomial fit p pressure t time u reference inlet velocity to the stator at midspan w relative velocity Of yaw angle / flow angle in the absolute frame of referrence 0 pitch angle / flow angle in the relative frame of referrence p density w total pressure loss
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