Research Of Combination Relationship Of Bulb Tubular Turbine Guide Vane And Blade

The development of renewable energy has great potential in our country,among which water energy is the most important one.Turbine is the core equipment of hydropower development,and its performance will directly affect the development rate of hydropower.Bulb tubular turbine plays an important role in the development of low head power station,which has the advantages of wide efficient area and small hydraulicloss.The storage capacity of tubular hydropower station is small,the regulation capacity is poor,and the coordinated working condition of units is easy to be damaged.Based on the actual operation of power station,the influence of the combination of guide vane and blade on the tubular unit was studied.The external characteristics and internal flow of the unit under the association of 4.5～8.3m head were studied through numerical calculation based on the real operation characteristic curves and model test curves of the power station.The performance of bulb tubular turbine is studied under typical operating conditions and low head operating conditions.The main work is as follows:Using the RNG k-ε turbulence model to carry out three-dimensional numerical calculation for the full flow channel,the external characteristics of the unit efficiency,flow rate and output under a certain head and the unit in the co-connected working condition are obtained,and the external characteristics curve of numerical calculation is drawn,which provides a theoretical basis for the real operation of the power station.The flow and efficiency of the unit increase first and then decrease with the increase of the guide vane opening.The head and output of the unit decrease in turn.When the water head changes about 0.5m,there will be 2° opening change of guide vane,which will cause 1%～2% change of unit efficiency.It is found that under the condition of small flow rate,the interaction between the main flow area of runner and the dead water area of draft tube forms the vortex structure.The vortex mainly appears at the side wall of draft tube diffusion and fills the whole draft tube flow area.There is obvious backflow phenomenon in the vortex area.Under the condition of large flow rate,the interaction force between runner and flow increases,and the flow pattern of the draft pipe is disarranged.The flow velocity of the draft pipe increases with the increase of the opening of the guide vane,and there is high-speed fluid and collision phenomenon on the side wall of the draft pipe.The unsteady numerical calculation is carried out for the combined conditions of small flow,intermediate flow and large flow of the turbine.Under the three conditions,the existence of draft tube of vortex was caused by the drainage cone.When the speed of the unit reaches the rated speed and the runner runs for 6 turns,the radial force of the unit is stable,and the radial force is distributed according to the simple harmonic function,and the radial force distribution is uneven under the conditions of large flow and small flow.The unit output is insufficient under the condition of small flow,so it is recommended to operate in the dry season.Under the condition of large flow,the unit output reaches the maximum,but the overall efficiency is low and unstable.It is recommended to operate for a short time in the flood season,and the unit can operate efficiently and stably under the condition of intermediate flow.When the trash rack of bulb tubular turbine is blocked in flood season,the unit will operate under low head condition.The operation characteristics of 6 working conditions are studied,which are 5.8m head,26° blade opening and 54°～64° guide vane opening.With the increase of guide vane opening,the flow and output of the unit increase obviously,but the efficiency and recovery coefficient of the unit decrease.It is found that the unit efficiency will decrease by 1% if the recovery coefficient of draft tube decreases by 2%～3%.When the water head fluctuates,it is recommended that the unit operate under the condition of small guide vane opening.Under the condition of low water head,the unit is mainly affected by low frequency pressure fluctuation.The main frequency of pressure at the runner inlet is 5.38 Hz,which comes from the rotation of runner and the circulation of runner provided by guide vane.In the draft tube,it is mainly affected by the low frequency pressure pulsation with frequency of 0.2Hz.The pressure pulsation coefficient increases along the draft tube,and the maximum pressure pulsation coefficient is 1.75%.