Numerical Study Of Non-Equilibrium Condensing Flow Based On The Modified Model

Non-equilibrium condensation will generate in the cascade flow path due to the low steam thermal parameters and high flow velocity in the low pressure stage of the steam turbine,generating a large number of tiny droplets and forming wet steam.Highspeed flow of wet steam mixed with a large number of tiny droplets will not only cause erosion of the moving blade which endanger the safe operation of the turbine,but also reducing the efficiency of the turbine.In this paper,for the non-equilibrium condensation phenomenon in the low pressure stage of steam turbine,numerical calculations combined with experimental results were adopted to evaluate the accuracy of the numerical calculation,and then adopt the “from simple to complex” and “from static to dynamic” solutions to study the characteristics of non-equilibrium condensation flow.Finally,a novel structure of dehumidification blade was proposed and the efficiency was evaluated.The main research contents and results of this paper are as follows:(1)Firstly this paper summarizes the experimental,theoretical and numerical studies on non-equilibrium condensation flow at home and abroad,then analyzes the control equations and models refer to the non-equilibrium condensation flow process and proposes two modified models related to non-equilibrium condensation on the existing basis.(2)The existing experimental data were used to verify the accuracy of the revised model.The non-equilibrium condensation flow both in the one-dimensional MosesStein nozzle and the two-dimensional Dykas stator cascade is numerically calculated using the modified model and the original model.The calculation results show that,the modified model can predict the position of the Wilson point and the thermodynamic parameters of the point more precisely in the Moses-Stein nozzle.Besides,the modified model can predict the surface pressure distribution of the blade and the shock angle of the tail more accurately in the Dykas static blade cascade(3)The modified model with verified accuracy was employed to study the characteristics of non-equilibrium condensation flow under different conditions.The calculation results showed that as the superheat of steam increased,the pressure rise position away from the inlet,but the value of pressure rise decrease,the initial position of the nucleation rate gradually shifts backward,the maximum nucleation rate gradually increases and the humidity gradually decreases,indicating that a higher inlet superheat will suppress the generation of non-equilibrium condensaing flow.Excessive expansion rate will lead to excessive recovery time,resulting in excessive nucleation rate,thus forming much more droplet growth cores,enhancing the process of heat and mass transfer in the rapid condensation region,and ultimately exhibiting higher humidity.With the increase of roughness,the main nucleation area gradually shrinks,the width of the nucleation zone formed near the nozzle outlet wall surface gradually increases,the humidity distribution area gradually decreases,and the area with higher humidity gradually increases,while the nozzle increases.The zone of zero-humidity zone near the wall surface gradually increases,and the humidity tends to be suppressed.However,the increase of the roughness will reduce the quality of the flow of the nozzle and thus reduce the function of the nozzle.(4)The non-equilibrium condensate flow at different dynamic and stationary blade positions in a certain stage of a steam turbine is studied.The calculation results show that,as the changes of relative position,the high pressure region near the leading edge of the stationary blade gradually shrink,the pressure in the flow channel gradually increases the position gradually moves upstream,and the value of the low pressure area also gradually increases.The low-pressure region near the suction edge of the leading edge of the moving blade gradually shrink,while the low pressure zone at the suction edge of the leading edge of the adjacent moving blade gradually enlarge,and the lowpressure region at the trailing edge suction surface gradually decreases.The high speed rotation of the rotor will cause periodic disturbances to the flow field in the upstream of the stator blade flow path and the moving blade cascade,and the period is consistent with the rotation period of the rotor blade cascade.In the stator cascade flow path,as the angle increases,the maximum nucleation rate region gradually moves up,and the maximum nucleation rate increases,but the nucleation rate region gradually decreases.(5)Based on the analysis of the characteristics of the non-equilibrium condensation process,a method was proposed to decrease the formation of humidity by guiding the high temperature steam at the leading edge of the blade to the nucleation zone and destroying the nucleation zone to inhibit the formation of the condensation core.The dehumidification effect of blades with different structures was evaluated.An improved dehumidification blade structure is proposed considering the structure of the blade is difficult to process,and the dehumidification efficiency of the blade with different channel angles is calculated and analyzed.