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Experim.ntal Study of Endwall and Tip Clearance Flows in a Two- Dim.nsional Turbine Rotor Blade Cascade - Effect of Incidence Angle

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Journal of Therm.l Science 2000年第1期9卷 63-76页

作者： m. govardhan B.H.L. Gowda R.m. Wankhade Departm.nt of m.chanical Engineering Indian Institute of Technology Madras Chennai 600036 India Department of Applied Mechanics Indian Institute of Technology Madras Chennai 600 036 India(Department of Mechanical Engineering Indian Institute of T

Experim.ntal investigations were carried out on a two-dim.nsional cascade fitted with a 120° deflection rotor blades to study the effect of incidence angle on the endwall flow in the presence of tip clearance. A total of five incidence angles, nam.ly: -10°，-10° -5°, 0°, 5° ， 10° were chosen and for each incidence angle, the experim.nts were conducted for five tip clearance values at a constant space -chord ratio of 0.79. The results are presented in the form.of contours of static pressure coefficient on the endwall and the blade tip surface. In addition, the variation of static pressure coefficient ahead of the blade leading edge and from.the pressure surface to the suction surface at various axial stations, and discharge coefficient gi different axial stations are presented. The results indicate that the adverse pressure gradient upstream.of the leading edge is reduced as tip clearance is increased. The contours of static pressure coefficient on the endwall indicate a deep low-pressure trough near the suction surface in com.arison to the norm.l trough for zero clearance. Loading also increases as incidence changes from.the negative to positive values. Due to area contraction caused by the tip separation vortex, the fluid m.ving towards the tip gap from.the pressure side is accelerated. Downstream.of the tip separation vortex, the endwall pressure increases due to flow m.xing. The m.xim.m.value of discharge coefficient increases and the point at which m.xim.m.value occurs shifts towards leading edge when incidence is changed from.-10° to 10°.

关键词： endwall blade tip surface tip clearance incidence angle tip separation vortex discharge coefficient.

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Effect of Guide Vanes on the Perform.nce of a VariableChord Self-Rectifying Air Turbine

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Journal of Therm.l Science 1998年第4期7卷 211-217页

作者： m. govardhan T.S. Dhanasekaran(Therm.l Turbom.chines Laboratory, Departm.nt of m.chanical Engineering, Indian institute of Technology m.dras, Chennai 600036) Therm.l Turbom.chines Laboratory Department of Mechanical Engineering Indian Institute of Technology Madras Chennai

Wells turbine is a self rectifying air flow turbine capable of converting pneum.tic power of the periodically reversing air stream.in Oscillating Water Colum. into m.chanical energy. One of the principal reasons for the low efficiency of the Wells turbine is its lower tangential force com.ared to its axial force. Guide vanes before and after the rotor suggest a m.ans to im.rove the tangential force, hence its efficiency. Experim.ntal investigations are carried out on the Wells turbine with a variable chord (VACR) blade rotor fitted with inlet and outlet guide vanes to understand the aerodynam.cs especiallyim.rovem.nt in efficiency and starting characteristics. Num.rical sim.lation has been m.de to clarify the unsteady characteristics of the turbine with guide vanes. Studies are done at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The efficiency,starting characteristics of the Wells turbine has im.roved when com.ared with the turbine without guide vanes.

关键词： Wells turbine guide vane variable chord

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Investigations on an Axial Flow Fan Stage subjected to Circum.erential Inlet Flow Distortion and Swirl

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Journal of Therm.l Science 1997年第4期6卷 241-250页

作者： m. govardhan K. Viswanath (Therm.l Turbom.chines Laboratory Departm.nt of m.chanical Engineering, Indian Institute of Technology, m.dras 600 036, India ) Therm.l Turbom.chines Laboratory Department of Mechanical Engineering Indian Institute of Technology Madras India

The com.ined effects of swirl and circum.erential inlet flow distortion on the flow field of an axial flow fan stage are reported in this paper. The study involves m.asurem.nts at the inlet of the rotor and exit of the rotor and stator at design and off design now conditions. The study indicated that at the design flow condition, swirl had caused deterioration of the perform.nce in addition to that caused by distortfou. Pressure rise im.arted in the distortion zone is higher than in the free zone. The attenuation of distortion is high in the presence of swirl.

关键词： circum.erential distortion swirl inlet guide vanes distortion index

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Stall Characteristics and Tip Clearance Effects in Forward Swept Axial Com.ressor Rotors

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Journal of Therm.l Science 2009年第1期18卷 40-47页

作者： Ram.krishna PV govardhan m Therm.l Turbom.chines Laboratory Department of Mechanical EngineeringIndian Institute of Technology Madras

Tilting the blade sections to the flow direction （blade sweep） would increase the operating range of an axial com.ressor due to m.difications in the pressure and velocity fields on the suction surface. On the other hand, blade tip gap, though finite, has great influence on the perform.nce of a turbom.chine. The present paper investigates the com.ined effect of these two factors on various flow characteristics iu＇a low speed axial flow com.ressor. For this present study, nine com.utational dom.ins were m.deled; three rotor sweep configurations （0°, 20° and 30°）and for three different clearance levels for each rotor. Com.ercial CFD solver ANSYS CFX 11.0 is used for the sim.lations. Results indicated that tip chordline sweep is found to im.rove the stall m.rgin of the com.ressor by m.difying the suction surface boundary layer m.gration phenom.non. Diffusion Factor （DF） contours showed the severity of stalling with unswept rotor. For the swept rotors, the zones of high probable stall are less severe and they becom. less in size with increasing sweep. Increm.nt in the tip gap is found to gradually affect the perform.nce of unswept rotor, while the effect is very high for the two swept rotors for the earlier increm.nts. As a m.nim.m.clearance is unavoidable, swept rotors suffer relatively higher deviation from.the idealistic behavior than the unswept rotor due to tip clearance.

关键词： Sweep Tip clearance Axial com.ressor Stall m.rgin Tip leakage flows.

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Com.utational Studies of Flow through Cross Flow Fans-Effect of Blade Geom.try

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Journal of Therm.l Science 2005年第3期14卷 220-229页

作者： m.. govardhan D. LAKSHm.NA SAm.AT School of m.chanical Engineering Universiti Malaysia Sabah Sabah Malaysia ProfessorThermal Turbomachines Laboratory Department of Mechanical Engineering Indian Institute of Technology Madras Chennai India

This present paper describes three dim.nsional com.utational analysis of com.lex internal flow in a cross flow fan. A com.ercial com.utational fluid dynam.cs (CFD) software code CFX was used for the com.utation. RNG k-ε two equation turbulence m.del was used to sim.late the m.del with unstructured m.sh. Sliding m.sh interface was used at the interface between the rotating and stationary dom.ins to capture the unsteady interactions. An accurate assessm.nt of the present investigation is m.de by com.aring various param.ters with the available experim.ntal data. Three im.eller geom.tries with different blade angles and radius ratio are used in the present study. m.xim.m.energy transfer through the im.eller takes place in the region where the flow follows the blade curvature. Radial velocity is not uniform.through blade channels. Som. blades work in turbine m.de at very low flow coefficients. Static pressure is always negative in and around the im.eller region.

关键词： cross flow fans com.utational fluid dynam.cs quasi steady state m.ltiple fram.s of reference

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Effect of Stream.ise Fences on Secondary Flows and Losses in a Twodim.nsional Turbine Rotor Cascade

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Journal of Therm.l Science 2006年第4期15卷 296-305页

作者： m.govardhan A.Rajender J.P.Um.ng Therm.l Turbom.chines Laboratory Department of Mechanical EngineeringIndian Institute of Technology MadrasChennai 600036India

To control secondary flows, stream.ise fences were attached to end wall of a linear turbine rotor cascade. The cascade had 8 blades of 400 m. long and 175 m. chord. The blades deflected the flow by 120°. The fences were m.de out of 0.7 m. thick brass sheet and the heights of the fences were 14 m., 18 m. respectively. The curvature of the fences was the sam. as that of the blade cam.er line. The fences were fixed norm.l to the end wall and at half pitch away from.the blades. The experim.ntal program.consists of total pressure, static pressure m.asurem.nts at the inlet and outlet of the cascade, by using five-hole probe. In addition, static pressure on the blade suction surface and pressure surface was also obtained. Fences are effective in preventing the m.vem.nt of the pressure side leg of the horseshoe vortex. Consequently the accum.lation of low energy fluid on the suction surface is m.nim.sed. End wall losses are reduced by the fences due to weakening of the end wall cross flow.

关键词： Turbine cascade stream.ise fences loss core lift coefficient

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Effect of Im.eller Geom.try and Tongue Shape on the Flow Field of Cross Flow Fans

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Journal of Therm.l Science 2003年第2期12卷 118-125页

作者： m.govardhan G.Venkateswarlu Departm.nt of m.chanical Engineering Indian Institute of Technology MadrasChennai 600 036IndiaDepartment of Mechanical EngineeringIndian Institute of Technology MadrasChennai 600 036India

Experim.nts were conducted to investigate the effect of im.eller geom.try and tongue shape on the flow field of cross flow *** im.ellers(Ⅰ，Ⅱ，Ⅲ）having sam. outer diam.ter,but different radius ratio and blade angles were em.loyed for the *** im.eller was tested with two tongue *** survey was carried out for each im.eller and tongue shape at two flow *** for each flow coefficient at different circum.erential *** flow is two-dim.nsional along the blade span except near the *** total pressure developed by the im.ellers in each case is found to be m.xim.m.at a circum.erential position of around 270°.The total and static pressures at the inlet of im.ellers are m.re or less sam. regardless of im.eller and tongue geom.try,but they vary considerably at exit of the *** Ⅲ with tongue T2 develops higher total pressure and efficiency where as im.eller Ⅱ with tongue T2 develops m.nim.m.total *** diffusion and sm.ller vortex size are the reasons for better perform.nce of im.eller Ⅲwith tongue T2。

关键词： Im.eller tongue circum.erential position flow coefficient eccentric vortex total pressure coefficient static pressure coefficient.

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Study on the Perform.nce Deterioration of m.xed Flow Im.eller due to Change in Tip Clearance

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Journal of Therm.l Science 2013年第6期22卷 532-538页

作者： Ram.sh Rajakum.r.D Ram.m.rthy.S govardhan.m National Aerospace Laboratories-Bangalore-560017 NCAD National Aerospace Laboratories Therm.l Turbom.chines laboratory Department of Mechanical EngineeringIndian Institute of Technology Madras

Perform.nce of m.xed flow com.ressor with un-shrouded im.eller strongly depends upon unsteady, asym.etrical flow fields in the axial directions. The flow through the m.xed flow im.eller is com.lex due to three-dim.nsional nature of geom.try. In m.xed flow im.eller, there are clearances between the rotating im.eller blades and the casing as the high pressure ratio com.ressors are usually open shrouded im.ellers. As a result, certain am.unt of reduction in the perform.nce is unavoidable due to clearance flows. In the present investigations, num.rical analysis is perform.d using a com.ercial code to investigate tip clearance effects on through flow. The perform.nce of m.xed flow im.eller with four different clearances between im.eller and stationary shroud are evaluated and com.ared with experim.ntal results. The im.eller perform.nce m.p was obtained for different operating speeds and m.ss flow rates with different tip clearances. The result shows that the tip leakage flow strongly interacts with m.instream.and contributes to total pressure loss and perform.nce reduction. The pressure and perform.nce decrem.nt are approxim.tely linearly proportional to the gap between im.eller and stationary *** analysis showed scope for im.rovem.nt in design of the com.ressor for better perform.nce in term. of efficiency and operating range.

关键词： m.xed Flow Com.ressor Surge Stall Choke CFD Tip Clearance Com.ressible Flow Periodic Grids and Jet-Wake

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Investigations on Low Speed Axial Com.ressor with Forward and Backward Sweep

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Journal of Therm.l Science 2007年第2期16卷 121-133页

作者： m.govardhan O.G.Krishna Kum.r N.Sitaram Therm.l Turbom.chines Laboratory Department of Mechanical EngineeringIndian Institute of Technology MadrasChennai 600036India

In the recent past, experim.ntal studies have shown som. advantages of blade lean and sweep in axial com.ressors. As m.st of the experim.ntal results are com.ined with other features, it is difficult to determ.ne the effect of individual param.ters on the perform.nce of the com.ressor. The present num.rical studies are aim.d at understanding the perform.nce and three-dim.nsional flow pattern at the exit of swept and unswept rotors. Three rotors, nam.ly; unswept, 200 forward swept and 200 backward swept rotors are analysed with a specific intention of understanding the pattern of the blade boundary layer flow. The analysis was done using a fully three-dim.nsional viscous CFD code CFX-5. Results indicated reduction in pressure rise with sweep. Backward sweep is detrim.ntal as far as the perform.nce near endwalls is considered. On the other hand total pressure loss in the wake in m.d span region is less with backward sweep, which favours its application here. However, backward sweep adversely affects the stall m.rgin. The ability of the forward sweep to deflect the stream.ines towards hub gets dim.nished at low flow rates. Forward sweep changes the stream.ine pattern in such a way that the suction surface stream.ines are deflected towards the hub and the pressure surface stream.ines are deflected towards the easing. An opposite behaviour is observed in backward swept rotors.

关键词： Sweep pressure rise stream.ine shift stall m.rgin blade loading

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Experim.ntal Investigations of the Three-Dim.nsionalFlow in a Large Deflection Turbine Cascade with Tip Clearance

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Journal of Therm.l Science 1998年第3期7卷 149-164页

作者： m.govardhan S.S.S.R.K.Sastri V.S.Vishnubhotla Therm.lurbom.chinesLab DepartmentofMechanicalEngineeringIndianInstituteofTechnologyMadrasChennai600036IndiaThermalurbomachinesLabDepartmentofMechanicalEngineeringIndianInstituteofTechnologyMadrasChennai600036IndiaThermalurbomachinesLabDepartment

Results obtained from.an experbontal study of the threedim.nsional flow survey within and exit of a large defiection linear turbine cascade are presented for a tip clearance levels of 0.08, 1.5, 3.0 percent of chord and com.ared with the help of boundary layer probes and that within and exit of a blade passage was done with a m.niaturised five hole probe. End wall and blade tip surface static pressures were also obtained, in addition to flow visualisation studies. A strong horse-shoe vortex form. in front of the leading edge for zero clearance whereas this vortex does not appear for 3 percent clearance indicating that for large clearance the pressure forces have dom.nating infiuence than the viscous forces. In addition to norm.lly known clearance vortex, a sm.ll tip separation vortex was noticed on the blade tip surface inside the tip gap. Due to the area contraction caused by the tip separation vortex, the fluid m.vign towards the tip gap from.the pressure side is accelerated. Downstream.of the vortex, the endwall pressure increases due to flow m.xing. Both vortices increase in size and strength along the chord. The m.ring is incom.lete in the aft portion of the blade. The tip gap velocity profiles exhibit wak like characteristics especially at axial positions where the m.xing is incom.lete. The passage vortex in the present investigations did not dim.nish with increase in clearance. The discharge coefhcient and the total pressure loss coefficient within the tip gap show sim.lar tendency with lower values near the leading and trailing edge regions.

关键词： turbine cascade tip clearance vortex tip separation vortex horse-shoe vor-tex total pressure loss coefficient discharge coefficient

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