Internal Flow And Aerodynamic Characteristics On The Variable-pitch Axial Fan With Two-stage Regulated Blade

With the increment of power installed capacity, the unit capcitiy of600MW~1000MW has been a main choice for large-scale power stations, meanwhile the variable-pitchaxial fan with two-stage regulated blade have been widely applied in forced draft fans,induced fans and primary fans. The stability operation of the fans provide an importantguarantee for safety production in power plants, while the impeller installation angle isone of the most important factors influencing the dynamic behaviors and stabilities ofaxial fans.A steady and three-dimensional flow field of a variable-pitch axial fan with two-stageregulated blade used in a600MW unit was simulated. The internal aerodynamics and theeffects of installation angle on the axial fan were investigated; the performances of fanwith compound guide vane and single long-guide vaneaxial fan were compared and thevariations of inner flow field under the conditions of different axial position,circumferential position and length of short guide vane were presented respectively.Meanwhile, fans global and local flow field characteristics with the abnormal bladedeviating positive and negative angles in the first-stage impeller, as well as thenon-synchronous adjustment of the first-stage and second-stage impeller were analyzed.Results show that, the overall performance of total pressure for second-stage impellerat the exit stream surface presents lower symmetry than the first-stage impeller，which isrendered as the high-pressure and sub-high-pressure zone distribution alternately. Thetotal pressure rise coefficient of impeller and diffuser coefficient of guide vane tend toaugment with increasing of installation angle, and the working capability of impeller anddiffusion capability of guide vane present to be remarkable in second-stage impellercomparing with those in first-stage impeller. The corresponding full pressure andefficiency present obvious superiority, especially efficiency, when the first stage guidevane adopts the compound guide vane with320mm length for the short-guide vanelocated at the inlet of first-stage guide vane and intermediate of two adjacent long-guidevanes. Under the installation angle of abnormal blade deviating with small angle, the fullpressure, efficiency, turbulent kinetic energy and acoustic source power levels change slightly. With the deviating angle Δβyincreasing, the performances deteriorate extremely,and the intensity of turbulent kinetic energy and noise unceasingly strengthens. Inaddition, the affected areas expand to a plurality of rotor passages as the oppositedirection of the impeller rotating. When the phenomena of non-synchronous adjustmentof the first-stage and second-stage impeller appears, the overall performance, thecapability of total pressure rise for single-stage impeller and the work capability ofabnormal blade itself on first-stage impeller abnormally, as well as the guide vaneefficiency, are inferior to those on the second-stage impeller abnormally, especially forthe performance of the fan with installation angle deviating in negative direction, except βy=12°.