Investigations of curved draft tubes with long exit cones

Autor: Gubin, M., Volshanik, V., Kazennov, V.
Zdroj: Power Technology and Engineering (formerly Hydrotechnical Construction); October 1974, Vol. 8 Issue: 10 p949-956, 8p
Abstrakt: Conclusions:
1.  An increase in the length of a curved draft tube having a standard LMZ elbow of series 4 from 3.64D1 to 15.0D1 leads to a considerable increase in the nonuniformity of discharge in the spans of the exit cone and the related energy losses also increase. As a result the turbine efficiency can at first increase and then decrease with lengthening of the tube.
2.  The change in turbine efficiency on lengthening the exit cone is different for tubes with a symmetric and asymmetric elbow. An increase in the tube length with an asymmetric elbow from 3.64D1 to 15.0D1 changes the turbine efficiency by 0.7–1.0% (on the model) and depends little on the turbine operating regime; in the case of a symmetric elbow the change in efficiency amounts to 0.5–3.6% and increases with increase in discharge. The optimal length of a tube with an asymmetric elbow is 4.0–5.0D1, and with a symmetric 9.0–11.0D1, for Q′I corresponding to the center of the main universal characteristic of the turbine, and the optimal length increases with increase in discharge. Shortening of a tube with an asymmetric elbow from 4.0D1 to 3.64D1 leads to a marked decrease in turbine efficiency.
3.  The presence of a splitter and the location of its nose in the entry section of the cone have a substantial effect on turbine operation. The absence of a splitter provides a higher turbine efficiency in regimes with large discharges and permits increasing its discharge capacity. In the presence of a splitter in regimes with large discharges the efficiency of the turbine can be increased by shifting the splitter nose leftward with respect to the flow. The optimal amount of shift should be established in relation to the type of turbine and its operating regime.
Databáze: Supplemental Index
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