Two new measuring techniques are discussed. They give, respectively, the distributions of the arc current in the directions parallel and transverse to the arc motion. They are applied to measurements on an arc, 1.6 mm in length, burning at up to 700 A, in air at atmospheric pressure, between 2 parallel copper electrodes and driven, at up to 200 ms" 1 , by a transverse magnetic field. The measured distribution profiles are nonsymmetrical in both directions. The current density at the arc foot is much larger than previously reported for the arc column. The transverse profile is characterized by a high-current core with 2 low-current wings.
A comprehensive flutter test program was performed at subsonic/transonic Mach numbers in a nonrotating Annular Cascade rig. This rig was designed to investigate negative incidence choke flutter and positive incidence stall flutter. The objective of the program reported here was to establish choke flutter criteria for use in design of axial flow gas turbine airfoils which operate in the subsonic/transonic aerodynamic environment. To realize this objective, a systematic and controlled experiment was conducted which allowed the documentation of flutter boundaries over an extensive range of aerodynamic and aeromechanical parameters. The data presented are from an experimental investigation of blade flutter related to compressor midstage rotor blades with emphasis on negative incidence and choke flutter. Flutter characteristics were established for three midstage airfoil designs that provide a range of solidity and flexural reduced velocity. Effects of inlet test conditions on the flutter boundaries were evaluated for each of the five configurations tested. Results indicate that at Af/M max =0.5, a 25% increase in design reduced velocity produced a 13% decrease in flutter incidence margin and a 23% increase in solidity resulted in a 16% decrease in flutter incidence margin. Effect of increasing inlet pressure is destabilizing with less effect at high inlet pressures. Inlet temperature is also destabilizing; a 30% increase in temperature resulted in an 18% decrease in flutter incidence margin.b h M Nomenclature half-chord, in. airfoil lateral deflection, in. fl°w incidence normalized by the maximum flow incidence obtained in the investigation cascade inlet axial Mach number at inner flowpath relative Mach number normalized by the maximum relative Mach number obtained in the investigation cascade test rig inlet total pressure, psia cascade test rig inlet total temperature, °R first flexural mode reduced velocity inlet air velocity relative to cascade, fps cascade inlet flow angle relative to axial plane, deg cascade inlet flow angle relative to axial plane that causes cascade to choke, deg = cascade inlet total pressure, P 01 , divided by standard day pressure (14.7 psia or equivalent) = total temperature, T 01 , divided by standard day temperature (518.6°R or equivalent) = solidity = air foil twist deflections, rad = first flexural mode natural frequency, rad/s
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