Study On The Type Of The Draft Tube And The Optimization Of The Equivalent Cone Angle

In this paper,using the modeling software UG 8.5,three-dimensional modeling of each over-current component of HL741-LJ-84 turbine of a hydropower station in Qinghai is carried out,secondarily the model is imported into ICEM-CFD for the mesh division,and finally imported into FLUENT software.The turbine is subjected to full flow field calculation under three conditions: small flow working condition,optimal working condition and large flow working condition.This paper aims to compare the hydraulic performance of standard concrete elbow draft tube and elliptical section metal-lined elbow draft tube and the effect of equivalent cone angle on the overall performance of the draft tube.Based on the original equivalent cone angle of 14° of HL741-LJ-84 turbine,the above two types of draft tube are used respectively,and the simulation calculation is carried out under three conditions of small flow condition,optimal working condition and large flow condition.From the streamline distribution map and the pressure cloud diagram,it can be seen that the secondary recirculation phenomenon in the concrete draft tube is not as obvious as that in the metal-lined draft tube under the small flow condition,and the flow line of the metal-lined draft tube diffusion section is more disordered under the large flow condition.Under the optimal working condition,the recovery coefficient of concrete draft tube reached 72.60%,and the recovery coefficient of metal liner water tube was only 70.2%,indicating that the hydraulic performance of concrete draft tube is better than the latter.On this basis,the flow field calculations of three different concrete elbow draft tubes with equivalent cone angles of 14°,16° and 18° were carried out under optimal conditions,and the recovery coefficients of the draft tube were 72.60%,respectively.73.74% and 70.31%,indicating that the concrete draft tube has the best hydraulic performance at an equivalent cone angle of 16°.From the perspective of numerical simulation,this paper makes a specific analysis and calculation on the optimal problem and optimization design of the draft tube,which has certain reference value for improving the economic benefit of the power station.