Research On Design Method Of Spiral Case Under Sediment-laden Conditions

HL741-LJ-84 turbines of a hydropower station on Longwu River in Qinghai Province suffer severe wear and tear of volutes due to their perennial operation in sediment-laden rivers,which seriously reduces the service life of the volute s.The scroll case of Francis turbine designed by the theory of equal velocity moment has a large inner wall velocity because of its small tail radius,which will cause severe wear and tear at the nose end of the scroll case when it runs in the sediment-laden river.For this reason,according to the average velocity law of several volute sections given by Clivchenko et al.,the hydraulic design of the volute is carried out separately.Four volutes designed by the theory of equal velocity moment and the meth od of given velocity distribution are numerically simulated in the whole flow passage of a hydraulic turbine.Through the analysis of absolute velocity,radial velocity,inlet circulation and liquid flow angle of the volute,as well as the blade of the run ner and draft tube,a better scheme of anti-sediment wear modification of the volute is selected.Through calculation,it can be concluded that the average velocity at the nose end of the volute designed by the method of equal velocity moment can reach thr ee times of the average velocity at the inlet section,wear can be very serious in sediment-laden rivers.In different volute design methods,the wrap angle of the last circular section is different.The smaller the wrap angle of the final circular section,the larger the area of each cross-section,the smaller the average velocity,and the better the anti-abrasion performance of the volute,but the worse the axisymmetry of the flow.When a given section velocity method is used to design the volute,the mor e the given velocity distribution deviates from the constant velocity moment method,the worse the symmetry of the flow,the smaller the average velocity of the section and the better the anti-abrasion performance.Among the two methods mentioned in this p aper,the method of equal velocity moment,the method of equal velocity and the method recommended by Clivchenko,the first design method recommended by Clivchenko is most suitable for turbines under sediment-laden conditions.