Masayuki Ogata

Flutter Limits and Behaviors of Flexible Webs Having a Simplified Basic Configuration in High-Speed Flow

Fluttering conditions were analyzed for webs with a simplified basic configuration with both leading and trailing edges fixed in a uniform flow. The predicted flutter limits are expressed in terms of a ratio of fluid force to tension (σ* ), a ratio of tension to bending stiffness (T*) and a reduced frequency f R . Three characteristic zones of the behavior are seen to appear depending on the magnitude of τ * For medium τ * of 1X10 3 to 1 X10 6 , flutter-limit values of σ * and f R remain nearly constant, respectively For low τ * ( 1 X 10 6 ) ripple-like modes tend to occur and σ * ,falls drastically and f R scatters much. Experimental flutter limits obtained in the wind tunnel were seen on the average to agree with the expected ones for the tested range of 9 X 10 2

Improvement of Stalling Characteristics of an Axial-Flow Fan by Radial-Vaned Air-Separators

An improved construction of air-separator device, which has radial-vanes embedded within its inlet circumferential opening with their leading-edges facing the moving tips of the fan rotor-blades so as to scoop the tip flow, was investigated with respect to the stall-prevention effect on a low-speed, single-stage, lightly loaded, axial-flow fan. Stall-prevention effects by the separator layout, relative location of the separator to the rotor-blades, and widths of the openings of the air-separator inlet and exit were parametrically surveyed. As far as the particular fan is concerned, the device together with the best relative location has proved to be able to eliminate effectively the stall zone having existed in the original solid-wall characteristics, which has confirmed the promising potential of the device. Guidelines were obtained from the data for optimizing relative locations of the device to the rotor-blades, maximizing the stall-prevention effect of the device, and minimizing the axial size of the device for a required stall-prevention effect, at least for the particular fan and possibly for fans of similar light-load fans. The data suggest the changing internal flow conditions affected by the device conditions.

Effects of Compact Radial-Vaned Air Separators on Stalling Characteristics of an Axial-Flow Fan

The stall-prevention effect of air separators incorporating radial vanes in place of the existing axial vanes was investigated on a low-speed, single-stage, lightly loaded axial-flow fan for effective and compact air separators of a simplified structure. From the survey, paying attention to several geometrical dimensions of the device, the following conclusions are obtained: (1) Simplified radial vanes made of flat plates could show strong stall-prevention effect comparable to those of the curved-vane type one. The most favorable ones showed no stall up to the fan shut-off conditions. (2) Radial heights of the recirculation passage within the air separator showed significant influences on the stall improvement. It should be larger than some critical size experimentally given in the study. (3) The axial length of the device should be larger than some critical size given experimentally in the study. Too much reduced axial length could give rise to an abrupt loss in the effect. (4) The optimum axial locations of the rotor-tip blade leading edge within the device inlet opening were found to lie near the center of the width of the inlet opening from both aspects of stall improvement and fan efficiency.

Experimental Study on the Characteristics of a Vibrating Elastic Plate Flow Generator

Flow characteristics by a Vibrating Elastic Plate Flow Generator (VEPFG) was investigated experimentally. The device was a plate made vibrated perpendicularly to itself at the leading edge. The flow was found to be generated for a narrow range of frequency around the resonance frequency, with its maximum at the resonance frequency. The induced flow rate and its efficiency were experimentally determined. The performances were relatively low compared with the analytically expected ones. The efficiency turned out to be of 10 per cent. On the basis of the visualized flow patterns, one of possible causes for the difference is attributed to the existence of unsteady large-scale discrete vortices at both the trailing edge and the side edges. The side-edge vortices are seen to reduce drastically the induced flow rate by the factor of more than two.

Effects of Blade Tip Clearances on the Suction-corner Performances of a High-load Axial Compressor Cascade

Strong adverse flows tend to occur in the suction surface/wall corner of high-load blade cascades of axial compressors. In a two-dimensional cascade wind tunnel test, effects of tip clearances on the cascade pressure coefficient Cp and flow structures in the corner were surveyed. Addition of a tip clearance was found to alter the flow conditions in the suction corner of axial compressor blade cascade. Tip clearance of 0.4 mm for the test blade of chord length of 100 mm in a typical high-load stator blade cascade increased the pressure coefficient Cp and lessened the corner loss coefficient compared with the cases with no clearance or with wider clearance. The issuing jet through the tip clearance of 0.4 mm was found to have eliminated strong vortices in the corner zone. It suggests a very useful means of improving the axial compressor performances.