We carried out investigations for the purpose of clarifying the rotor outlet flow fields with rotating stall cell in a diagonal-flow fan. The test fan was a high-specific-speed (n s = 1620) type of diagonal-flow fan that had 6 rotor blades and 11 stator blades. It has been shown that the number of the stall cell is 1, and its propagating speed is approximately 80% of its rotor speed, although little has been known about the behavior of the stall cell because a flow field with a rotating stall cell is essentially unsteady. In order to capture the behavior of the stall cell at the rotor outlet flow fields, hot-wire surveys were performed using a single-slant hotwire probe. The data obtained by these surveys were processed by means of a double phase-locked averaging technique, which enabled us to capture the flow field with the rotating stall cell in the reference coordinate system fixed to the rotor. As a result, time-dependent ensemble averages of the three-dimensional velocity components at the rotor outlet flow fields were obtained. The behavior of the stall cell was shown for each velocity component, and the flow patterns on the meridional planes were illustrated.Keywords Fan, Internal flow, Rotating stall, Stall cell, Unsteady flow A diagonal-flow fan has relatively high efficiency, a low noise level, and a wide operating range. However, when its specific speed becomes high, its pressure/flow-rate curve tends to indicate unstability by a positive gradient in the low flow range that is similar to that of an axial-flow fan. It is well known that the rotating stall is the main cause of this unstable characteristic, and a flow field with a rotating stall indicates remarkable un- , 1999;Moore and Greitzer, 1986;Poensgen and Gallus, 1996; SaxerFelice et al., 1998) have investigated the flow field with a rotating stall cell. However, there are very few studies of unsteady flow fields in diagonal-flow fans. Kaneko and colleagues (1993, 1995, 1997) tried to measure an unsteady flow field with a rotating stall in a high-specific-speed diagonal-flow fan using hot-wire and pressure probes. From that series of studies the unsteady flow characteristics of a rotating stall cell were clarified to some extent. Since then, Shiomi and colleagues (2000) have reported the behavior of a stall cell in a pressure field using a total pressure probe in a high-specific-speed diagonal-flow fan, but the detailed flow pattern has been unknown.Most surveys of the internal flow fields of turbomachines have been performed using a phase-locked averaging technique, because the flow field includes the periodical fluctuations caused by the rotor blades' passing. Under rotating stall conditions, however, another fluctuation caused by the stall cell's propagating at a speed different from that of the rotor is superimposed on the flow field. Therefore, it is impossible to analyze a flow field with a rotating stall cell by using the ordinary phase-locked averaging technique. In order to clarify a flow field with a rotating stall cell and the beh...
