Investigation On Aerodynamics Performance And Flow Characteristic Of A Inlet Structure For Steam Turbine Low Pressure Cylinder

Steam turbine is one of the most important prime movers.It is not only used in compressors,pumps,blast furnace fans and other rotating equipment,but also constitutes the three main bodies of thermal power generation with boilers and generators.It continuously provides power supply for industrial production and social life.In actual operation,its internal flow increases or decreases with the change of grid load.As the key link of arranging the upstream flow reasonably at the inlet of the full cycle pressure stage,the internal flow condition of the inlet structure will not only affect its aerodynamic performance,but also affect the enthalpy drop in the upstream cylinder and the efficiency of the downstream cylinder pressure stage and other performance parameters.The inlet structure is composed of three parts:volute cavity,transverse guide vane and outlet diversion.In order to investigate inlet structure aerodynamic performance and flow characteristics,full 'three-dimensional numerical simulation method has been used to investigate flow field,and the physical entity of the numerical model is measured by experiment,and the experimental data is compared with the numerical results to verify the reliability of the numerical method.In addition,a new type of outlet diversion form of annular cavity is studied and compared with the traditional axial flow diversion form.The results show that the total pressure loss coefficient of the whole inlet structure and its volute cavity,transverse guide vane and outlet diversion increases with the increase of the flow rate,and the higher the flow rate,the faster the increase.The distribution of the total pressure loss at the outlet of the volute cavity is not uniform along the circumference,and it is transmitted to the outlet of the whole inlet structure.The flow situation in the middle diameter and near the wall of the blade passage at different circumferential positions of the transverse guide vane is different,which is mainly caused by the fluctuation of the air flow angle at the outlet of the upstream volute cavity along the circumferential direction,but after the guide vane's guide function,the air flow angle along the circumferential direction is basically the same at the outlet of transverse guide vane.There is no obvious difference in the total pressure loss coefficient between the two outlet diversion forms,but the annular cavity form has a more uniform at the outlet.This optimization of flow angle uniformity mainly comes from the radial direction.According to the analysis of the flow characteristics in the inlet structure,the flow in the volute cavity mainly shows the positive pressure gradient balances centrifugal force from the outside to the inside,and can basically maintain the tangential flow.Through the analysis of secondary flow vorticity,it is found that there is a pair of vortices in the upper and lower part of the volute cavity.With the development of the flow,the process of generation,development to disappearance occurs.In this process,with the continuous entrainment of the low-energy fluid near the wall nearby and the irreversible viscous dissipation of the vortex itself,it causes a large flow loss,which is also the main reason for the non-uniformity of the total pressure loss coefficient at the outlet of the volute cavity.Because the radial pressure gradient dominates the flow in the transverse guide vane passage and offsets the transverse pressure gradient between the vanes,it does not pick up the channel vortex in passage,the main vortex structures in the transverse guide vane passage are pressure side leg and the suction side leg of horseshoe vortex.Because of the difference of the outlet flow angle of the volute cavity,the development trend of the two branches of horseshoe vortex in the guide vane passage at different circumferential positions is.different.In the two kinds of outlet diversion forms,the radial flow is transformed into the axial flow,and vortex appears at the 900 turning point.The difference is that in the annular cavity form,except for most of the flow out along the axial direction,a small part of the flow enters the cavity and forms a closed area.