Efficiency of the small-sized turbine stages with small outlet angle of nozzles
The paper is devoted to the task of increasing the efficiency of small-sized turbines, which used in ship main and auxiliary mechanisms. The article presents results of research of a small-sized turbine, which have nozzles with exit angle from 5° to 9°. Influence on the efficiency different constructive and regime factors and their combinations is analyzed. The following factors are considered in the paper: the ratio of the pressure in front of the turbine nozzle to the pressure behind the turbine (π<sub>T</sub>); the ratio of the area of the outlet section of the nozzle to the area of the critical section ( f<sup>-</sup>); constructive input angle of the rotor blade channels (β<sub>1K</sub>); constructive exit angle of the nozzle (α<sub>1K</sub>); the ratio of the circumferential speed of the rotor to the critical speed of sound at the outlet of the nozzles (λ<sub>u</sub>). The analysis is based on simulation techniques using regression models obtained on the basis of the results of the model experiment conducted in the following range of varying operating and con constructively factors: f<sup>-</sup> = 1...2.82; α<sub>1K</sub> = 5°...9°; β<sub>1K</sub> = 8°...14°; π<sub>T</sub> = 2.35...47.1; λ<sub>u</sub> = 0...0.44. Optimization results showed that the efficiency of a small-sized turbine with the nozzle design discussed can reach 62% with f<sup>-</sup>= 1; α<sub>1K</sub> = 5 °; β<sub>1K</sub> = 8 °; π<sub>T</sub> = 19.7; λ<sub>u</sub> = 0.44.