Потери энергии в рабочем колесе при переходном и малорасходном режимах

Abstract

An approach to the determination of energy losses in a stage with a large fanning is considered during its operation in low-flow rate and transient modes. At present, high-power turbines (200 MW and above) are operated in a wide range of modes and low-pressure cylinders with working blades lwb ≈ 940–1200 mm are exposed to operating conditions in which the last and penultimate stages don’t generate mechanical energy, but absorb that generated stages of high and medium pressure cylinders. Such operating modes require an assessment of the level of energy losses in the stages of large fanning, especially for the stages of the low-pressure cylinder of cogeneration turbines of combined heat and power plant, which are often operated with completely closed control rotary diaphragms, i.e. at steam flow rates not exceeding 1,5–2,5 % of the flow rate entering the turbine. The evaluation of energy losses in accordance with the structure of the flow at low flow rates and the adopted model of the flow through the stage in the presence of formed structures, namely, the main flow (entering in the stator blades); the rotating vortex in the rim clearance; the bushing tear-off of flow, consisting of a series of sequentially located rotating vortices, expedient performs in a first step for the main flow, including trickles corresponding to the areas of end losses or areas conjugated with the bushing tear-off of flow and the rotating vortex in the rim clearance. It is noted that the energy losses in the main flow passing through the stage increase linearly with a decrease in the relative volumetric flow rate of the working fluid. The maximum level of integral energy losses in the main flow is achieved with a "pure" ventilation mode and can be made up approximately 30 % heat drop per stage during its nominal mode of operation which corresponding to the maximum efficiency at the crown of the stage.