Profile modification of tubular turbine blades based on flow field computation

Aimed at the problems occured during the operation process of fixed-blade shaft extension tubular turbine generator set in a power plant such as the large deficiency in power output from its nominal one and the accompanying vibration and noise,the flow field in the flow passage of turbines was numerically evaluated with CFD numeric simulation.It was found that there was some defect and deficiency in the original hydraulic model selected for the power plant and as well in the manufacturing process of the turbine.According to the result of numeric simulation and its analysis the technical remodelling only was made for the runner,that is the chords of blade's airfoils on the blade span from its middle to tip were extended with consideration of the requirement of blade's strength.By doing so,the spanwise variation of blade's profile(airfoil) was made as consistent with the pattern of third-order Bessel function for profile modification of the blades.Meantime,the satting angles of the blade sections were increased.It was shown by the simulation computation after modification of the runner that its efficiency was improved a lot compared with that of original hydraulic model,the maximal efficiency being improved by 2.5% and the efficieney at nominal point_2%.It was verified by the practice of operation of the remodelled runner that not only the vibration was eliminated and noise reduced during the operation of the unit but the maximal output of the generator also reached 88% of its nominal capacity even in the case of operation with lower hydraulic parameters than the nominal ones(with the head less by 20%).Consequently,this turbine could develop not only its nominal power but also possessed extra capacity of power generation if it operated with nominal hydraulic parameters.