Effect Of Swirl Inflow On Bulb Turbine’s Diffuser Pressure Recovery

The bulb turbine is a kind of reaction type wheel, whose opening angle of guide vanesand opening angle of runner vanes can be adjusted, and has a flat efficiency curve. As bulbturbine’s draft tube which can improve pressure through recovering the runner outlet’s kineticenergy in order to keep high efficiency, the performance of a straight diffuser with a largercone angle has important effect on bulb turbine’s total efficiency. In water turbine’s design andresearch, the flow fluid analysis and performance prediction are common ways, they areconnected closely and reflect each other. So far, numerical simulation calculation andsimulation flow field have been the latest research angle in this field at home and abroad.As the first part of bulb turbine’s draft tube, conical diffuser’s performance is connecteddirectly to the level of draft tube recovering runner outflow’s kinetic energy. So the paperdiscussed conical diffuser’s performance firstly in the chapter2, then discussed bulb turbine’stotal performance and confirmed its on-cam performance in the chapter3, finally in thechapter4discussed draft tube’s flow pattern and under the on-cam performance discussed thelogical relationship between draft tube’s flow pattern and runner’s outflow, got suchconclusions like that:(1) numerical simulation technology can simulate internal flow pattern of calculationmodel and do performance prediction truly;(2) a cone diffuser could improve the outlet’spressure through recovering water’s axial kinetic energy to reduce water’s energy;(3) theturbulence’s model, boundary layer, the number of volume grid and inlet’s swirling flow allmade some effect on the accuracy of the numerical simulation calculation’s result;(4) thecomputational fluid dynamics technology could predict bulb turbine’s performance, and makethe best matching of guide vanes’ opening angle and runner vanes’ opening angle, now therunner outlet had some positive swirl flow, the draft tube’s internal flow was best, so far therunner was connected with draft tube, that would apply more reliable theoretical basis for the water turbine’s further optimization design;(5) new standards were put forward to judge thebest flow in draft tube—kinetic energy distortion rate Iekand energy deficiency in draft tubeD, to recognize when the flow pattern in draft tube was optimal, the pressure recoverycoefficient Cpof draft tube was maximum, Dwas minimum, and the Iekat the outlet of drafttube was also minimum.On the basis of previous studies, the deep research of cone diffuser and bulb turbine wascarried out in this paper, which further discussed the mechanism of internal water’s flow,found out new rules, and strengthen the understanding of both, finally applied more reliabletheoretical basis and the verification method for bulb turbine’s research and development.