A study was made of the flow in radial nozzle cascades using an air test rig and a water test rig. In the air test rig, three cobra probes were used in circumferential and spanwise traverses to determine the total pressure variations in the flow field at three radii downstream of the nozzles at which static pressure was also measured. The tests were made on two sets of nozzle blades having heights of 0.148 in. (0.376 cm) and 0.200 in. (0.508 cm), at trailing edge angles (measured from circumferential direction) of 15, 20, and 25 deg, and at two flow Mach numbers of approximately 0.2 and 0.35. The test results presented in this paper, in the form of loss coefficients and flow angles, were flow-weighted and averaged. Flow visualization in the air test rig was made on the walls bounding the nozzle blades using the graphite power-oil mixture technique. Additional tests were made on the water test rig using dye injection technique. Photographs were obtained showing clearly formation of secondary flow around each nozzle blade in the form of the leading edge vortex. The test results confirm the existence of the leading edge vortices reported peviously, and extend their study to the radial nozzle cascades.
The paper describes application of the theory of wave reflection in turbomachines to rotor blade vibrations measured in an axial compressor stage. The blade vibrations analyzed could not be explained using various flutter prediction techniques. The wave reflection theory, first advanced in 1966, is expanded, and more general equations for the rotor blade excitation frequencies are derived. The results of the analysis indicate that all examined rotor blade vibrations can be explained by forced excitations caused by reflecting waves (pressure pulses). Wave reflections between the rotor blades and both the upstream and downstream stator vanes had to be considered.
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