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1.
Performance of mixed flow compressor with un-shrouded impeller strongly depends upon unsteady, asymmetrical flow fields in the axial directions. The flow through the mixed flow impeller is complex due to three-dimensional nature of geometry. In mixed flow impeller, there are clearances between the rotating impeller blades and the casing as the high pressure ratio compressors are usually open shrouded impellers. As a result, certain amount of reduction in the performance is unavoidable due to clearance flows. In the present investigations, numerical analysis is performed using a commercial code to investigate tip clearance effects on through flow. The perform- ance of mixed flow impeller with four different clearances between impeller and stationary shroud are evaluated and compared with experimental results. The impeller performance map was obtained for different operating speeds and mass flow rates with different tip clearances. The result shows that the tip leakage flow strongly inter- acts with mainstream and contributes to total pressure loss and performance reduction. The pressure and per- formance decrement are approximately linearly proportional to the gap between impeller and stationary shroud. The analysis showed scope for improvement in design of the compressor for better performance in terms of effi- ciency and operating range. 相似文献
2.
Investigation of a centrifugal compressor and study of the area ratio and TIP clearance effects on performance 总被引:2,自引:0,他引:2
Mahdi Nili-Ahmadabadi Ali Hajilouy-Benisi Mohammad Durali Farhad Ghadak 《热科学学报(英文版)》2008,17(4):314-323
In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and dif- fuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was stud- ied numerically. The impeller area ratio was changed by cutting the impeller exit axial width from an initial value of 4.1 mm to a final value of 5.1 mm, resulting in an area ratio from 0.792 to 0.965. For the rotor with exit axial width of 4.6 mm, performance was investigated for tip clearance of 0.0, 0.5 and 1.0 mm. Results of this simula- tion at design point showed that the compressor pressure ratio peaked at an area ratio of 0.792 while the effi- ciency peaked at a higher value of area ratio of 0.878. Also the increment of the tip clearance from 0 to 1 mm resulted in 20 percent efficiency decrease. 相似文献
3.
为研究不同宽度叶顶间隙对亚音速半开式离心叶轮性能与内部流场的影响,对某工业用半开式离心叶轮选用不同形式和几何参数的叶顶间隙,通过数值模拟得出结论:随叶顶间隙宽度减小,叶顶附近湍动能减少,离心叶轮通道压比和效率更高,但是失速裕度也变小;在本研究范围内,综合考虑性能和失速裕度,叶顶间隙宽度为0.4 mm时最优;叶顶间隙宽度对泄漏流和主流相互作用有一定影响;随叶顶间隙宽度减少,叶顶间隙泄漏流量减少,本文的分析结果为离心压缩机的工业设计提供了一定参考。 相似文献
4.
The pressing demand for future advanced gas turbine requires to identify the losses in a turbine and to understand the physical mechanisms producing them. In low pressure turbines with shrouded blades, a large portion of these losses is generated by tip shroud leakage flow and associated interaction. For this reason, shroud leakage losses are generally grouped into the losses of leakage flow itself and the losses caused by the interaction between leak- age flow and mainstream. In order to evaluate the influence of shroud leakage flow and related losses on turbine performance, computational investigations for a 2-stage low pressure turbine is presented and discussed in this paper. Three dimensional steady multistage calculations using mixing plane approach were performed including detailed tip shroud geometry. Results showed that turbines with shrouded blades have an obvious advantage over unshrouded ones in terms of aerodynamic performance. A loss mechanism breakdown analysis demonstrated that the leakage loss is the main contributor in the first stage while mixing loss dominates in the second stage. Due to the blade-to-blade pressure gradient, both inlet and exit cavity present non-uniform leakage injection and extrac- tion. The flow in the exit cavity is filled with cavity vortex, leakage jet attached to the cavity wall and recircula- tion zone induced by main flow ingestion. Furthermore, radial gap and exit cavity size of tip shroud have a major effect on the yaw angle near the tip region in the main flow. Therefore, a full calculation of shroud leakage flow is necessary in turbine performance analysis and the shroud geometric features need to be considered during turbine design process. 相似文献
5.
This paper presents preliminary measurements of a 2-stage axial turbine with shrouded rotor cavities. The research facility and measurement techniques are reported. The flow field at both inlet and outlet was measured using 5-hole probes as well as temperature probes. The measurement results indicate that the inlet flow field is periodical in the tangential direction due to the influence of the first-stator leading-edge. The horse-shoe vortexes cause substantial flow blockage and turbulence near the endwall. Unsteady measurements of the rotor radial tip clearance show that one of the second-rotor blades has a little bigger clearance than the others. 相似文献
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INTRoDUCTI0NThetipleakaeflowisnowrecognizedasanimpor-tantsourceoflossesinbothcompressorsandturbines,asasourceofcoolingprobleminturbinesandasourceofinstabilityincomPressorsandfans.Manyturbo-maChinimPellersarenotshroudedandtheleakaeflowthroughthetipgaPofthebladeisanunavoidablefaCtorwhichdeterioratestheperformance.Den-tonandCumpsty[1]melltionedabouttwodistinctandequallyimportantaspects.tothetipclearanceflows.First,thereisareducti0ninthebladeforce,there-fore,theworkdone.Thisoccursbecausethe… 相似文献
8.
Weiguang Huang~ Shaojuan Geng~ 《热科学学报(英文版)》2007,16(2):115-120
This paper reports a numerical study on the process from normal operating conditions to rotating stall in a cen-trifugal compressor with vaned diffuser.The purpose is to better understand the flow characteristics near stallpoint under the interactions between centrifugal impeller and vaned diffuser.Numerical results show that undercertain conditions just preceding stall point the tip leakage vortex begins to fluctuate at roughly half of the bladepassing frequency.This phenomenon is similar to rotating instability in axial compressors.With the flow rate re-duced further the impeller stalls and five stall cells propagating at a frequency of 85 percent of impeller rotationspeed are found. 相似文献
9.
Generally speaking,main flow path of gas turbine is assumed to be perfect for standard 3D computation.But in real engine,the turbine annulus geometry is not completely smooth for the presence of the shroud and associated cavity near the end wall.Besides,shroud leakage flow is one of the dominant sources of secondary flow in turbomachinery,which not only causes a deterioration of useful work but also a penalty on turbine efficiency.It has been found that neglect shroud leakage flow makes the computed velocity profiles and loss distribution significantly different to those measured.Even so,the influence of shroud leakage flow is seldom taken into consideration during the routine of turbine design due to insufficient understanding of its impact on end wall flows and turbine performance.In order to evaluate the impact of tip shroud geometry on turbine performance,a 3D computational investigation for 1.5-stage turbine with shrouded blades was performed in this paper.The following geometry parameters were varied respectively:-Inlet cavity length and exit cavity length,-Shroud overhang upstream of the rotor leading edge and downstream of the trailing edge,-Shroud radial tip clearance,The aim of this paper is to isolate the influence of shroud and cavity geometry modifications on turbine aerodynamic performance and to obtain clear trends of efficiency changes caused by different tip shroud geometry.Moreover,interaction between leakage flow and mainstream for different shroud configuration is also highlighted in order to penetrate into the physical mechanisms producing them.Due to the limitations of the model selected in this paper,the aim of research is not to put forward the design rules of turbine shroud.However,the results obtained from this work will be useful to the integrated design and optimization of turbine with shrouded blades. 相似文献
10.
Syed Noman Danish Shafiq Rehman Qureshi Abdelrahman EL-Leathy Salah Ud-Din Khan Usama Umer Chaochen Ma 《热科学学报(英文版)》2014,23(6):523-534
Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor. Stage characteristics are explored for various tip clearance levels, axial spacings and circumferential clockings. Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle, meridional gas passage and camber distributions in order to have a true comparison with conventional design. Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance. Linear-equation models for correlating stage characteristics with tip clearance are proposed. Comparing two designs, it is clearly evident that the conventional design shows better performance at moderate flow rates. However; near choke flow, tandem design gives better results primarily because of the increase in throat area. Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation. 相似文献
11.
This paper presents an experimental investigation of effects of one kind of tangentially non-uniform tip clearance on the flow field at an exit of a compressor cascade passage.The tests were performed in a low-speed large-scale cascade with the uniform tip clearance and the non-uniform clearance.The three-dimensional flow field was measured at the exit at three incidence angles of 0°,5°,and 8° using a mini five-hole pressure probe.The measurement results show that the non-uniform tip clearance can moderate the leakage flow and blow down more low-energy fluids at the tip corner and decrease the accumulation of low-energy fluids which cause the flow blockage in the blade passage.In the meantime,the non-uniform clearance can weaken the tangential migration of the low-energy fluids in the endwall boundary layer and reduce the secondary loss and the flow blockage in the tip region. 相似文献
12.
Numerical simulation on the effect of tip clearance size on unsteadiness in tip clearance flow 总被引:1,自引:0,他引:1
Unsteadiness of tip clearance flow with three different tip clearance sizes is numerically investigated in this paper. NASA Rotor 67 is chosen as the computational model. It is found that among all the simulated cases, the un- steadiness exists when the size of the tip clearance is equal to or larger than design tip clearance size. The relative total pressure coefficient contours indicate that region of influence by tip leakage flow augments with the increase of tip clearance size at a fixed mass flow rate. Root Mean Square contours of static pressure distribution in the rotor tip region are provided to illustrate that for design tip clearance (1.1% tip chord) the strongest fluctuating region is located on pressure side of blade near leading edge, while for the larger tip clearance (2.2% tip chord), it is in the region of the interaction between the shock wave and the tip leakage flow. 相似文献
13.
Effects of suction side squealer tip on the performance of a low-speed axial compressor 总被引:1,自引:0,他引:1
This paper presents the investigation of the effects of suction side squealer tip on the performance of an axial compressor.The experiment is carried out in a single-stage large-scale low-speed compressor.The investigated tip geometries include flat tip as the baseline and suction side squealer tip.The tip clearance of the baseline is 0.5% of the blade span.The static pressure rise characteristic curves of both the rotor and the stage are measured.The flow field at the exit of the rotor is measured by a 5-hole probe under design and off-design conditions.The static pressure on the endwall of the rotor passage is also obtained.The results show that the pressure rise characteristic curves obtained by measuring the pressure on the end wall are almost unchanged by using the suction side squealer tip.The measuring results of the 5-hole probe show the static pressure and the total pressure in tip region is slightly greater than that of the flat tip at the design condition at the exit of the rotor.It also leads to greater av-eraged static pressure rise and total pressure.At the near stall condition,the averaged static pressure and total pressure is lower than the baseline which is related to the redistribution of the blade load caused by the suction side squealer tip. 相似文献
14.
为量化评估工程应用的气冷低压涡轮带冠转子叶片的叶尖间距大小对涡轮气动性能的影响,综合现有涡轮部件试验能力,以单级轴流低压涡轮性能试验件为基础,通过控制圆度的机加方式磨削转子外环内壁以实现叶尖间距的变化,采用控制冷气流量比的方法,开展5次不同叶尖间距大小的涡轮级性能试验,得到多工况下涡轮效率、换算流量和换算功率等特性参数。采用加载冷气及考虑转子叶冠结构的数值模型进行三维仿真计算,并与试验结果对比分析。研究表明:叶尖间距由0.6 mm增加至3.2 mm,低压涡轮流通能力增大1%,叶冠泄漏量增多3.4%,但做功能力下降2.3%。涡轮效率变化与叶尖间距大小近似呈线性关系,叶尖间距每增加1 mm,效率约降低0.7%,同时,叶尖间距的增加导致了叶冠腔的旋涡结构、气流掺混及主流入侵强度逐渐增大,引起动叶总压损失的增大,叶尖间距增加至3.2 mm导致叶间位置总压损失由0.88增至2.3。 相似文献
15.
A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolatedaxial compressor rotor is presented,intending to better understand the flow mechanism behind stall control meas-ures that act on tip clearance flow.Under the influence of injection the unsteadiness of self-induced tip clearanceflow could be weakened.Also the radial migration of tip clearance vortex is confined to a smaller radial extentnear the rotor tip and the trajectory of tip clearance flow is pushed more downstream,So the injection is benefi-cial to improve compressor stability and increase static pressure rise near rotor tip region.The results of injectionwith different injected mass flow rates show that for the special type of injector adopted in the paper the effect ofinjection on tip clearance flow may be different according to the relative strength between these two streams offlow.For a fixed injected mass flow rate,reducing the injector area to increase injection velocity can improve theeffect of injection on tip clearance flow and thus the compressor stability.A comparison of calculations betweensingle blade passage and multiple blade passages validates the utility of single passage computations to investi-gate the tip clearance flow for the case without injection and its interaction with injected flow for the case with tipinjection. 相似文献
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Three-Dimensional Viscous Numerical Simulation of Tip Clearance Flow in Axial-Flow Pump 总被引:1,自引:0,他引:1
Changming Yang Cichang Chen Jinnuo Wang Quankai JiMechanical Engineering Institute Southwest Jiaotong University Chengdu Energy Department Sichuan University of Science Technology Chengdu 《热科学学报(英文版)》2003,12(3):231-233
The blade tip clearance flow in axial-flow pump is simulated based on three-dimensional N-S equations, RNG k -e turbulence model, and SIMPLEC algorithm. It shows that numerical results agree well with experiment data measured by 5-hole probe through validation. Flow fields at the blade tip and velocity distribution at the exit of rotor are analyzed in detail. The numerical results show that the increase in tip clearance reduces hydro-head, especially at small flow rate. Experiment equipment is also introduced. 相似文献
19.
H ongwu ZHANG Xiangyang DENG Jingyi CHEN Weiguang HUANG . Institute of Engineering Thermophysics Chinese Academy of Sciences P.O. Box Beijing China . Graduate School Chinese Academy of Sciences Associate Professor 《热科学学报(英文版)》2005,14(3):211-219
Introduction Background It is well known that the rotor tip clearance flow has profound effects on the performance and stability of axial compressor (Wisler[1], Howard[2]). Numerous studies on the tip clearance flow were carried out in the past fifty years. Rain[3] proposed a model to predict the loss due to tip leakage flow assuming that the kinetic energy of the leakage flow velocity component normal to the mean chamber line would be dissipated. Lakshminarayana[4] developed a model to pre… 相似文献
20.
Effects of rim location, rim height, and tip clearance on the tip and near tip region heat transfer of a gas turbine blade 总被引:5,自引:0,他引:5
Jae Su Kwak Jaeyong Ahn Je-Chin Han 《International Journal of Heat and Mass Transfer》2004,47(26):5651-5663
Effects of the rim height and the tip gap clearance on the heat transfer coefficients on the blade tip and near tip regions were measured with two different rim geometries. The heat transfer coefficient distributions were measured using the transient single color capturing liquid crystals technique. Rims were located along (a) the pressure and the suction side (full-rim case) and (b) the suction side of the blade tip (suction side rim case). The rim heights were (a) 2.1%, (b) 4.2%, and (c) 6.3% and the blade tip gap clearances were (a) 1.0%, (b) 1.5%, and (c) 2.5% of the blade span. Tests were performed on a five-bladed linear cascade placed in a blowdown facility. The overall pressure ratio, inlet total pressure to exit static pressure, was 1.2, and the Reynolds number based on the exit velocity and the axial cord length was 1.1 × 106. The turbulence intensity level at the cascade inlet was 9.7%, and the inlet and exit Mach number were 0.25 and 0.59, respectively. It was found that higher rims reduce the heat transfer coefficients on the tip and shroud, but the reduction on the pressure and suction sides was not significant. The suction side rim case provided lower heat transfer coefficients on the blade tip and near tip regions than the full-rim case. 相似文献