Turbomachinery

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Bulb turbines are applied on low head and large discharge hydro resources, which have slight impact on environment. Since dynamic pressure at the runner outlet of bulb turbines is relatively higher than that of other types, pressure recovery in draft tube directly affects on turbine efficiency performance. Many experimental studies have been reported on the relation between pressure recovery and diffuser configuration as well as effect of inlet swirl flow. there are, however, only a few reports investigating on draft tube configurations in hydro turbines having rotating runner. Authors investigated effects of inlet cone angle and runner hub configuration on the draft tube pressure recovery as well as efficiency of bulb turbine. In the present paper, it is shown that a bell shaped draft tube consisting of upstream conical diffuser with large angle and downstream conical one with small angle brings about better performance.

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