高低齿迷宫气封在汽轮机级中应用的数值研究（英文）

cause its structure is simple relatively and cost is low，which is now widely used in steam turbine of moderncoal·fired power plants. The traditional labyrinth sealbelong to non-contact gas seal，it does not require lu。

brication，allow free thermal expansion，easy mainte。

nance，and it is not subject to speed restrictions ' 。

so labyrinth seal is widely used as the sealing device inthe steam turbine and gas turbine. However.in 0r-der to prevent mechanical interference problem causedby the machining or installing，through-flow gap mustbe retained in labyrinth sea1.so labyrinth seal can noteliminate leakage flow， which restrain leakage flowthrough increasing flow resistance with a step by stepexpansion，and by the limitation of the equipment axiallength，the leakage flow of the labyrinth seal is largerIf we can minimize the leakage loss of labyrinth seal，the efficiency and power of the steam turbine or gasturbine will be improved effectively， the power plant2013年4月 10日收到，5月3日修改 国家自然科学基金委创新研究群体(51121004)资助第-作者简介：张宏涛(1971-)男，博士研究生，高级工程师。研究方向：叶轮机械设计与数值模拟。E-mail：hevkid###gmail.con。

The complexity of the internal flow in gas seal，re-suiting in a very long period， experimental researchwas the only way to study gas seal flow characteristicsand design the new gas seal means[819.With the de-velopment of computer technology and the level of eom。

putational fluid dynamics，numerical study on air sealinternal flow，improvement on air seal design level，was gradually paid attention in the turbine manufactur-ing industry and was developed.Numerical simulationon flow，mechanism analysis and design methods studyof seal is a new issue，its contents include the BUmeri。

cal method，the aerodynamic characteristics，interac。

tion mechanism of the leakage flow and mainstream，and the flow computation method and modeling of sealthat suitable for engineering application[ 。，. In this paper，the calculation model was createdbased on the actual structure of the stator diaphragmlabyrinth seal of the eighth stage of some high pressuresteam turbine，by using the commercial software CFX，the simulation on the three dimensional flow field 0fseal is carried out，through analysis of the calculationresults，the sealing mechanism of theseal with rotor step was revealed，stage tooth laby-and ways to fur-21期 张宏涛，等：高低齿迷宫气封在汽轮机级中应用的数值研究 6O95ther improve the labyrinth seal tightness was explored，reference for the engineering design of the type sealwas provided。

1 Numerical simulation methods1.1 Computation modelThe three-dimensional computational model isshown in fig.1.In order to explore the influence of thelabyrinth seal on the aerodynamic performance of theactual turbine structure，a 1.5 stage turbine with bal-ance hoes of some high-pressure steam turbine is usedas the geometric mode1. In fig.1，S1，R1 denote thestator and rotor of the eighth stage.and is the ninthstage stator，the lower colored surface is the surface ofthe moving blade impeller，the surface of the balancehole and the surface stator diaphragm labyrinth seal，and the top colored surface is surface of the tip laby-rinth sea1。

In2Fig.1 The three-dimensional computational modelThe specific structure of the stator diaphragm lab-yrinth seal is shown in figure 2，wherein the a)and b)denote the structure of the stator diaphragm labyrinthseal and the structure of the seal tooth，respectively。

Under the bottom of the diaphragm，due to the relativemotion between the diaphragm and the rotor，there is agap between them，in order to minimize the leakageflow flux from this gap，a stepped labyrinth seal isused.The color surface in figure 1 a)is the rotor sur-face，the seal tooth of the stator diaphragm labyrinthseal has two long teeth and 12 short teeth，the 12 shortteeth is separated into three adjacent groups by the twolong teeth。

a)Diaphragm labyrinth sealb、The sealtoothFig.2 Th e model of the stator diaphragm labyrinth seal1.2 Computation gridsBecause of the complexity of the calculation mod·el，several different meshing software was used in themeshing process， structured and unstructured gridmethods was joint used.The structured grid was usedto the rule geometry and cascade flow channel(as thefig.3)，and the unstructured grid was used to the ir-regular geometry(as the fig.4)。

As shown in figure 2，the stator diaphragm laby-rinth seal is composed of seal chamber and steps，theseal tooth is sharp structure. Th e flow space of thistype seal structure is small，the flow field structure iscomplex，and there is large-scale vortex structure inthe seal space，and there is also small-scale vortex incorner and strong viscosity role on wall，in order tosimulate the flow field of the seal accurately，fewernumber of grids and better mesh quality must be given。

figure 5 shows the grid distribution of the seal，the21期 张宏涛，等：高低齿迷宫气封在汽轮机级中应用的数值研究 6097of the computational domain with the outside world，the Inl and In2 is the inlet interface of the 8th stagestator and static diaphragm ，and the Outl and the Out2is the outlet interface of the 9thdiaphragm.The specifc valuesinterface is shown in table 1。

stage stator and staticof the inlet and outletTable 1 The interface boundary conditionsInl，In2 Total pressure 8.015 MPa，Total temperature 690.25 KOutl Static pressure 6.022 3 MPa，Circumferential averageOut2 Static pressure 6.0223 MPa，Cross-section型 !!ra2 Numerical results discussion2.I Typical flow structure analysisThe flow structure between two steps of the rotor isthe typical representative flow in the internal flow fieldof stator diaphragm labyrinth sea1.Figure 6 shows thevelocitv vector of the flow between the second and thirdstep.From Figure 3 we can see，in the two short teethagainst the step，the leakage flow occurred three timesturning and induced many different size vortex in fivegas seal chamber.Firstly，leakage flow formed a jet tothe seal chamber behind the step when flow through thesmall gap that the first short teeth against the step，be·hind the step.under the action of short and long tooth，the leakage flow turn to the rotor surface at first time，about at half location of the second chamber，adherentflow formed.Leakage jet flow driven the stagnationfl0w in the first and the second seal chamber，form edtwo clockwise and two counter-clockwise rotation bigvortex.respectively.Through the small gap created bylong tooth and rotor concave surface，the leakage jetflow entered the subsequent two seal chamber and con-tinued to keep adherent flow，until it hit the side wallof the latter step.and occured the second time turn-ing.which was almost vertically upward. Then，theleakage flow entered the seal chamber above the stepthrough the gap composed by the penultimate shortteeth and the side surface of next step. On the role ofthe small gap created by the last short tooth and nextstep，the leakage flow occured the third time turning，the turning degree was close to 90 degrees，and jetedout through the small gap，began the similar flow pat-tern at the next two steps. In the three seal chamberbehind the long seal tooth，the leakage flow inducedthree pairs of large eddy with opposite rotation direc。

Velocitym/sFig.6 The flow structure between the twosteps of labyrinth sealFigure 7 showed the streamline distribution in theseal in the meridional view.From the disorder degree0f streanfiine in the figure，we can see the turbulence0f the leakage flow in the seal chamber，and the stre-amline distribution in the meridional plane showed thelarge eddy coherent structures of the turbulence flow inthe sea1 chamber clearly.The streamline and velocityvect0r in the meridional plane showed that，there wascomplex vortex motion in every seal chamber，especial-1v in the three seal chambers near the step，leakagefl0w occurred three times large angle turning，formedtwo large.scale vortex with opposite rotation direction inevery seal chamber. Dramatic flow tuming would in-crease the impedance of the seal to leakage flow，highstrength large-scale vortex conducive to kinetic energydissipation of leakage flow，so it can be seen，settingsteps in seal was a important way for improving the per。

The radial height is signifcantly greater than theaxial width of the seal chamber size in this paper，the21期 张宏涛，等：高低齿迷宫气封在汽轮机级中应用的数值研究with straight-through labyrinth seal，the stagnation en-thalpy contours of thermodynamic process on the enthalpy-entropy diagram is same，but there are two dif-ferent points of their Fenno line：First，the Fenno lineof the seal in this study is under the one of the straight-through labyrinth seal，Second，the Fenno curvaturethis study is greater than the one of the straight-throughlabyrinth sea1. So，to achieve the same sealing effectwith the straight-through labyrinth seal，the seal in thisstudy requires only a smal number of teeth. Furthermore.from figures 5 and 6 it can also be seen，to theseal of this paper，the pressure drop and velocity in-crease of the leakage flow through a back tooth is al-ways bigger than through the front one，which is con-sistent with the general variation law of the flow param-eters in the labyrinth seal along the flow direction。

Fig.9 Distribution of pressure contours2.3 Seanng mechanismFrom the flow phenomena shown in figure 6 tolOcan be seen，the nature of the seal of the long andshort tooth labyrinth seal with rotor steps is same withthe straight-through type labyrinth sea1. However，compared with the straight-through type lab yrinth seal，the seal of this study has a step rotor，long ot short sealtooth，diferent tip clearance sizes，these changes inthe seal structure can improve the sealing perform anceof the seal from three aspects：(1)reduce the volumeratio of the small clearance of the tooth top，strengthenthe throttling effect of the leakage flow，promote theconversion of pressure energy to kinetic energy of theleakage flow.(2)increase the wall area of the leakageflow through the relative movement，enhance the flowturbulence intensity in the seal chamber，exacerbatethe dissipation of the leakage flow from kinetic energyto heat energy.(3)large angle turning times of leak-age flow increase three times，and the impedance ofseal to leakage flow increase signifcantly.This showsthat the optimization matching of rotor steps，long andshort teeth and the size of gap of labyrinth seals，whichcan further improve the aerodynamic perform ance oflabyrinth sea1。

3 ConclusionsFig.10 Distribution of Mach number contoursIn this paper，three-dimensional flow field numer-ical simulation on the eighth stator Diaphragm Laby-rinth Seal of a HP steam turbine was carried out bycommercial software CFX ，the sealing mechanism ofthe labyrinth seal was explored.The analysis of the nu-merical simulation results show that，in order to sup-press the leakage flow，the labyrinth seal，through aseries of alternating series of tooth tip clearance andseal chamber，applied the gradual strengthening throt-tle therm odynamic process to leakage flow，which canconvert pressure energy into kinetic energy and kineticenergy dissipation into heat energy.Reasonable matchof the rotor steps，the long and short tooth and the gap6100 科 学 技 术 与 工 程 l3卷size，can expand the wall area of the role of the rela-tive motion，increase the turning direction of the leak-age flow， and strengthen the throttle effect of everysmall top tooth gap to leakage flow，and improve theaerod) namic characteristics of the labyrinth seal fur-thermore。

Refefences1 Tian Bo，Kou Lei，Lou Mabao.Hold brush seal with excellent Per-formance.Gas Turbine Technology，2003；16(3)：21-242 Gamal A M，Vance J M.Labyrinth seal leakage tests：tooth profile，tooth thickness，and eccentricity efects. ASME Paper GT 2007-27223.20O73 Li Jun，Yan Xin，Song Liming.Arview of scaling teehnolores on tu-mmachinery Thermal Tarbine，2008；37(3)：141-1474 TIM P，RALF M. Modelling the labyrinth seal discharge coefficientusing data mining method s.ASME Paper GT 2010-22661，20105 Ning Zhe，Zhao Yi，Wang Shengpeng.Using adranced steam sealtechmology to nlprove steam turbines efficiency.Thermal Turbine，2009；38(1)：15-176 Stof H.Incompressible flow in labynnth sea1.J Fluid Mech，1980；100：159- l657 James H W.CFD Analy8is to Improve Performance of LabynnthSeals.NERC NEWS，Summer 1999；13(1)：348 Vakili A D，Meganathan A J，Michaud M.An experimental and nu-merical study of labyrinth seal flow.ASME Paper GT 2005-68224，20059 Denecke J，Dulenkopf K，Witig曼 Experimental investigation of thetotal temperature increase and swirl development in rotating labyrinthseals.ASME Paper GT 2005-68677，200510 Prekwas A，Athavale M，Hendricks IL Progress in advanced model-ing of turbine engine seals.AIAA Paper，AIAA-94-2803，199411 Heidegger N J，Hall E J，R Delaney A. Parameterized Study ofhigh-speed compressor seal cavity flow. AIAA Paper，AIAA-1996-2807.1996Numerical Study on the Application of Stepped LabyrinthSeal in Turbine StageZHANG Hong-tao ，WANG Xiang.feng ，GU Zhong-hua ，HAN Wan-jin(Colege of Energy science and engineering，Harbin Institute of Technology ，Harbin 150001，P.R.China；Harbin Turbine Company Limited ，Harbin 150046，P.R.China)[Abstract] In order to study the flow characteristics and sealing mechanism of the labyrinth seal used in turbinewith actual structure，numerical simulation on the three-dimensional flow field of one and a half turbine stage withbalance holes and the labyrinth seal structure were carried out by using the commercial software CFX，and the de-tailed analysis of the flow characteristics and sealing mechanism of the static diaphragm stepped labyrinth seal werecarried out.The results show that：compared with straight-through labyrinth seal，in the stator diaphragm，rotorwith stepped teeth labyrinth seal can make the leakage flow occur turning repeatedly，produce numerous large eddycoherent structure and disorder small vortex，and strengthen kinetic energy dissipation of the leakage flow，whichcan increase sealing performance of the stator diaphragm obviously.Optimization matching of rotor steps，high andshort teeth and the size of gap of labyrinth seals，which can further improve the aerodynamic perform ance of laby-rinth sea1。

[Key words] turbine stage labyrinth seal leakage flow balance hole numerical simulation