Calculation of the Energy Loss for Tip Leakage Flow in Turbines

A commercial N-S solver has been employed for simulation and investigation ofthe unsteady flow field inside the tip clearance of a turbine rotor. The main objective of thispaper is to introduce a new method of energy loss calculation for the flow field in tip clearanceregion of a turbine rotor blade. This method can be easily used in all kinds of flow fields. Regionsof high viscous effects have been found to be located near the shroud rather than the blade tip. Itis shown that the time-averaged loss of energy in tip leakage flow is dissimilar for differentrotor blades. This result is a helpful hint that can be taken by blade designers to designnon-uniform rotor blades with different geometric and aerodynamic loads to minimize the energy loss.

COMPUTATIONAL AND EXPERI-MENTAL STUDY ON TIP LEAKAGE VORTEX OF CIRCUMFERENTIAL SKEWED BLADES

In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors, including the radial rotor, the forward-skewed rotor and the back- ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the experiments, the two-dimensional plane particle image velocimetry （PIV） system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can display clearly some characteristics of the tip leakage vortex, such as the origination position of tip leak- age vortex, the development of vortex strength, and so on. Compared with the radial rotor, the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the forward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors, the velocity of the vortex in the forward-skewed rotor is th6 highest in the circumferential direction and the lowest in the axial direction.

Experiment on Effect of Tip Clearance Leakage Flow on Heat Transfer of Turbine Outer Ring

The cascade model was tested using transient liquid crystal temperature measurement technology.The effects of main flow Reynolds number,blowing ratio and tip clearance height on the convective heat transfer coefficient of the turbine outer ring were studied.Two feature lines were marked on the turbine outer ring corresponding to the position of the blade.The conclusions are as follows:The tip clearance leakage flow has a great influence on the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the blowing ratio are kept constant,gradually increasing the main flow Reynolds number will result in an increase in the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the main flow Reynolds number are kept constant and the blowing ratio is gradually increased,the convective heat transfer coefficient of the turbine outer ring is almost constant.The heat transfer coefficient of the turbine outer ring surface is little affected by the blowing ratio;The clearance height has great influence on the heat transfer characteristics of the turbine outer ring.Under the typical working condition in this paper,when the tip clearance height ratio is 1.6%,the convective heat transfer coefficient of the outer surface of the turbine is the highest.

Correlation between Aerodynamic Noise and Velocity Fluctuation of Tip Leakage Flow of Axial Flow Fan

In the present paper the attention is focused on correlation between fan noise and velocity fluctuations of tip leakage vortex around rotor blade of a low pressure axial flow fan at the maximum pressure operating point. We measured time fluctuating velocity near the rotor tip around the rotor blades by using a hot-wire sensor from a relative flame of refer- ence fixed to the rotor blades. As the results, it is clear that the velocity fluctuation due to tip leakage vortex has weak periodicity and the hump portion appeared in its spectrum. If the flow rate was lower than the design condition, the tip leakage flow became to attach to the following blade and the sound pressure level at frequency of velocity fluctuation of this flow was increased. The correlation measurements between the velocity fluctuation of tip leakage flow and the aerodynamic noise were made using a rotating hot-wire sensor near the rotor tip in the rotating frame. The correlation between the velocity fluctuation due to tip leakage flow and acoustic pressure were increased due to generation of weak acoustic resonance at the maximum pressure operating point.

EXPERIMENTAL INVESTIGATION OF TIP CLEARANCE FLOW FOR AN AXIAL FLOW FAN ROTOR

The flow field in the tip region of an axial ventilation fan is investigated with a particle image velocimeter （PIV） system at the design condition. Flow fields with three different tip clearances are surveyed on three different circumferential planes, respectively. The phase-locked average method is used to investigate the generation and the development of a tip leakage vortex. The result from PIV system is compared with that from a particle dynamics anemometer（PDA） system. Both data are in good agreement and the structure of the tip leakage vortex for the rotor is illustrated. The characteristic of a leakage vortex is described in both velocity vectors and vortical contours. The unsteadiness of the leakage vortex and the position of the vortex are surveyed in detail, which interprets the discrepancy between the numerical simulation and PDA experimental results to a certain extent. The center loci of tip leakage vortex at different times and the mean center loci of the leakage vortex are displayed particularly. Finally, the trajectories of the tip leakage vortex by the experimental measurement are compared with predictions from the existing models for high speed and high-pressure compressors and turbines when appropriately interpreted. A good agreement is obtained.

Effect of Tip-Blade Cutting on the Performance of Large Scale Axial Fan

The effect of tip-blade cutting on the performance of a large scale axial fan was investigated using computational fluid dynamics(CFD)methods.Experiments verified the numerical simulations.The original fan was compared with the one with tip-cutting in terms of dimensionless characteristic and aerodynamic performance in tip region under the conditions of the maximum efficiency point and near-stall point.The results showed that double leakage flow occurred in tip clearance at maximum efficiency point and spillage of leakage flow from leading edge occurred in tip-blade region at near-stall point for the both two fans;and that tip-cutting with 6% of blade height could reduce the intensity of tip-leakage vortex and increase flow capacity in tip blade region,and hold the stall margin almost the same as the original fan.The maximum efficiency of the fan with tip-cutting was improved by1%,and the ability of total pressure rising was obviously greater than the original fan.

Numerical Simulation of Active Control on Tip Leakage Flow in Axial Turbine

In an effort to reduce the blade tip clearance leakage in turbine designs, this article aims to numerically investigate the effects of active jet-flow injected from the blade tip platform upon the blade tip clearance flow. A CFD code integrated with dense-correction-based 3D Reynolds-averaged Navier-Stokes equations together with the well-proven Reynolds stress model (RSM) is adopted. The variation of specific heat is taken into consideration. The effects of jet-flow on the tip clearance flow are simulated ...

叶片破损对压气机性能的影响

为了研究叶片破损对压气机内部流场的影响机理,本文针对带有破损的跨音速压气机叶片进行气动性能变化规律和机理研究。通过NASA rotor 37实验结果验证了计算方法的准确性,利用数值仿真研究了叶片破损对压气性能的影响规律,并对2种典型工况下叶片破损前后的流场结构进行对比分析,探讨引起性能变化的具体原因。研究表明:叶片破损会导致压气机的压比降低0.6631%、绝热效率降低0.7877%,且压气机的稳定裕度降低更为明显。叶尖破损主要对叶顶流场结构产生影响,使叶顶区域泄漏流增强,当其与激波相互作用时,通道内产生了流动堵塞和流动损失。本文研究成果可为实际服役中的航空发动机特性评定提供理论参考。

叶顶间隙对蜗壳式混流泵流动特性影响研究

采用计算流体力学(CFD)数值模拟技术,研究了蜗壳式混流泵在不同叶顶间隙下的水力性能及内部流动特性。通过对流场、涡流和压力分布的分析,揭示了叶顶间隙变化对泵装置扬程、效率及运行稳定性的影响。结果表明,随着间隙尺寸的增大,混流泵的整体效率逐渐下降,且对大流量工况的影响尤为显著。同时,叶顶间隙的增大会导致叶轮区域泄漏涡的增强,影响泵的运行稳定性。

半开式离心叶轮叶顶泄漏诱发流道流动堵塞特性研究

为探究半开式离心叶轮叶顶泄漏量诱发的流道中流动堵塞作用,采用大涡模拟对流场进行精确计算,基于流动堵塞预估模型对叶顶间隙0.5、1.0和1.5 mm的3种半开式离心叶轮在不同流量工况下的流动堵塞特性进行研究,发现在叶轮流道内存在流动堵塞峰值,且在3种叶顶间隙下均在截面2处,在经过截面2之后流动堵塞发生大幅度的减小,并在后面4个截面发生小幅度的波动;通过对不同叶顶间隙、不同流量工况下在叶轮尾缘处相对流动堵塞作用的分析,发现尾缘处的流动堵塞在不同叶顶间隙下,随流量的变化具有相同的趋势,相对流动堵塞均在1.0Q_(d)时达到最小值,在0.6Q_(d)时出现峰值;然而流动堵塞在相同流量下与叶顶间隙的关系不是单一的线性关系,且存在一个最优叶顶间隙在设计工况点达到最小的流动堵塞情况;同时通过对泄漏涡发展情况的观察,发现泄漏涡的破碎和位移会增大叶片尾缘处的流动堵塞;通过对叶片静压差的分析,发现运行流量对叶片载荷的影响不大,然而叶顶间隙的改变会大大影响叶片载荷,同时对叶片尾缘处的流动堵塞造成影响。

基于Omega涡识别理论的自适应空化流动模型

液体火箭发动机涡轮泵内存在多种空化类型,其发生机理有所不同,现有数值计算方法通常采用同一套模型预测所有类型空化,导致预测精度不足。为提高复杂空化流动的计算精度,提出了自适应空化流动模型。基于先进的Omega涡识别理论和ZGB空化模型建立了相变系数自适应调整方法,以涡轮泵内两种典型空化(附着空化和泄漏涡空化)为对象,利用翼型实验对模型进行了验证。首先对比了几种涡识别方法的差异,发现Omega方法对阈值不敏感且物理意义明确,适合作为相变系数的取值依据;分析了相变系数对附着空化和泄漏涡空化的影响规律及两种典型空化的形成机理。结果表明:自适应模型相比ZGB模型,对泄漏涡空化的预测精度在大间隙下提升了约181%,小间隙提升了约27%,对附着空化的预测更接近实验结果;附着空化是吸力面脱落涡形成的原因,间隙泄漏流场的涡带和剪切层空化是由间隙泄漏涡和分离涡共同作用形成的。

环形电极等离子体激励控制透平叶顶间隙泄漏流动研究

为探究等离子体激励对叶顶泄漏流动的影响,基于非对称阻挡介质放电等离子体激励的数值模型,提出了环形电极的阻挡介质放电等离子体激励模型。将等离子体激励产生的体积力耦合至雷诺平均Navier-Stokes (RANS)方程组的动量方程中,数值研究了3种等离子体激励电压(9、13、17 kV)和3种激励频率(8、10、12 kHz)的透平叶顶泄漏流动特征。结果表明:环形电极等离子体激励显著改变了叶顶间隙的压力分布,在叶顶间隙内部和叶顶的两侧诱导形成大尺寸涡系结构,阻碍压力侧的主流进入叶顶间隙,有效抑制了动叶叶顶泄漏流动;在激励频率一定时,随着激励电压的增加,叶顶泄漏流动引起的总压损失减弱,但过高的激励电压会造成额外的诱导涡损失;激励电压保持不变,激励频率的增大对叶顶间隙的高压区域无明显影响,而叶顶两侧的诱导涡得到增强并挤压相邻的通道涡,叶栅通道120%轴向弦长处截面的总压损失进一步降低,13 kV激励电压、12 kHz激励频率工况具有最低的总压损失系数,相比无等离子体激励降低了16.12%。研究阐明了等离子体激励电压与激励频率对透平叶顶区域流场以及叶栅气动性能的影响规律。

离心叶轮失速涡结构演化与耦合特征研究

为深入解析离心压气机旋转失速的涡流耦合演化机理,基于Eckardt离心叶轮全通道非定常数值模拟数据,利用涡系识别法和傅里叶频谱分析等方法研究了失速工况下叶轮中关键涡流结构的空间分布特征及非定常演化规律,发现失速流场同时存在两类涡流结构:叶片前缘龙卷风涡和叶顶泄漏涡,两类流动结构交替演化、相互作用,形成了以63%叶轮转速周向传播的失速团,促使离心叶轮失速。具体体现为:叶顶泄漏涡形成并发展,裹挟、牵引叶片前缘分离涡从叶顶开始剥离,直至完全从叶片吸力面脱落。脱落后的分离涡沿周向运动,受到叶片阻挡产生溢流,该溢流流体在叶片压力面与吸力面横向压差的作用下演变为龙卷风涡,该龙卷风涡在周向运动过程中被叶片“截断”为两段而后向下游扩散并逐渐耗散消失。之后新的叶顶泄漏涡又逐渐兴起,形成下一个涡流演化周期。两种涡结构此消彼长、周而复始,共同构成了失速演化特征。

自循环机匣提高轴流泵稳定性的参数化研究

为了探究有效扩大轴流泵稳定运行范围的方法,针对轴流泵进行自循环机匣处理的单通道定常数值模拟,分析周向覆盖比例、抽吸口位置和喉部高度对水泵扩稳性能的影响规律,并揭示自循环机匣对轴流泵扩稳的改善机理.结果表明,抽吸口位置保持不变,扩大周向覆盖比例和喉部高度都可以增大流量裕度,但设计点效率降低;喉部高度为1.8 mm的自循环机匣流量裕度随着抽吸口位置的后移先增加后降低,效率先降低后增加,说明在叶顶上方存在一个最佳位置.在研究的范围内,流量裕度最大达到5.93%,设计点的效率最低降低1.12%.通过自循环机匣处理,使叶顶泄漏流与主流在叶顶上方相互作用形成的堵塞区面积有所减小,从而可以扩大轴流泵流量范围和提升小流量工况效率.该研究可为轴流泵在自循环机匣的端壁处理方式下扩稳提供参考.

间隙宽度对轴流泵叶顶间隙涡流影响的数值分析

针对轴流泵不同间隙宽度下间隙涡流特性问题,采用数值模拟方法研究了某轴流泵3种叶顶间隙宽度(0.15、0.45、1.20 mm)下的间隙泄漏涡流特性。结果表明,相同流量下,当间隙宽度从0.15 mm增大到1.20 mm时,间隙分离涡区增大,同一平面位置的涡心强度增大。不同叶顶间隙宽度下,叶顶间隙区域的湍动能分布趋势相似,即从叶顶间隙入口处开始沿径向先增大后减小直到轮缘,在分离涡形成附近湍动能达最大值。此外,沿泄漏涡轨迹泄漏涡涡心涡量减小,压力增大,表明前缘附近容易产生空化。对于极小的间隙(0.15 mm),主流大部分流动不能通过间隙,叶顶分离涡仅发生在叶片压力侧转角;对于1.20 mm的间隙,高湍动能叶顶分离涡发生在间隙区,分离涡与剪切层连接从叶片脱离,然后缠绕在涡核外侧,最终被泄漏涡夹带。在间隙附近存在不同的涡量层可将湍流注入泄漏涡。研究成果可为轴流泵的水利优化设计提供参考。

基于示迹线方法的压气机内部流动显示试验

为了揭示压气机转子叶顶泄漏流和静叶吸力面分离流动的形态及演变趋势,采用示迹线显示空气流动的方法对某低速轴流压气机转子叶顶间隙流动及静叶吸力面复杂流动进行了直接观测。结果表明:转/静子叶片上的示迹线直观形象地显示了转子叶顶泄漏流动和静叶吸力面分离流动的形态及演变趋势;随着压气机节流,转子叶顶泄漏流抗衡主流的“力量”不断增强,导致叶顶泄漏流的影响区域不断向上游拓展,到达近失速工况时,泄漏流与主流的交界面与叶顶前缘平齐;随着压气机节流,静叶吸力面上的流动分离区不断向静叶前缘扩展,到达近失速工况时,50%叶高以下静叶吸力面一侧出现了大面积的回流区。

Effect of blade tip geometry on tip leakage vortex dynamics and cavitation pattern in axial-flow pump

A series of blade tip geometries, including original plain tip, rounded tip on the pressure side and diverging tip towards the suction side, were adopted to investigate the effect of blade geometry on tip leakage vortex dynamics and cavitation pattern in an axial-flow pump. On the basis of the computation, it clearly shows the flow structure in the clearance for different tip configurations by the detailed data of axial velocity and turbulent kinetic energy. The in-plain trajectory, in aspects of the angle between the blade suction side and vortex core and the initial point of tip leakage vortex, was presented using the maximum swirling strength method. The most striking feature is that the inception location of tip leakage vortex is delayed for chamfered tip due to the change of blade loading on suction side. Some significant non-dimensional parameters, such as pressure, swirling strength and turbulent kinetic energy, were used to depict the characteristics of tip vortex core. By the distribution of circumferential vorticity which dominates the vortical flows near the tip region, it is observed that the endwall detachment as the leakage flow meets the mainstream varies considerably for tested cases. The present study also indicates that the shear layer feeds the turbulence into tip leakage vortex core, but the way is different. For the chamfered tip, high turbulence level in vortex core is mainly from the tip clearance where large turbulent kinetic energy emerges, while it is almost from a layer extending from the suction side corner for rounded tip. At last, the visualized observations show that tip clearance cavitation is eliminated dramatically for rounded tip but more intensive for chamfered tip, which can be associated with the vortex structure in the clearance.

高压涡轮动叶叶尖掉块对气动性能及振动的影响

【目的】高压涡轮损伤条件下运行状态对燃气轮机性能和振动会产生一定影响,而目前准确评估整机是否可以继续服役的手段较为缺乏,为此开展高压涡轮动叶叶尖凹槽磨损掉块对气动性能及振动变形的影响研究。【方法】采用三维数值仿真方法,以原动叶完整叶尖凹槽结构为基准,通过仿真分析了5种不同叶尖凹槽掉块形状对高压涡轮典型气动性能及动叶振动特性的影响规律。【结果】动叶叶尖凹槽叶盆侧掉块,叶背侧掉块,尾缘掉块,叶盆和尾缘同时掉块,叶盆、叶背和尾缘同时掉块,分别造成高压涡轮效率下降0.44%、1.6%、0.03%、0.67%、3.2%;不同动叶叶尖凹槽形状对动叶的振动变形影响较小,尾缘掉块会减小动叶的变形。【结论】综合气动性能及振动变形的影响分析,对于动叶叶尖凹槽的叶盆掉块、尾缘掉块或两者同时掉块的叶片可以继续使用,而对于叶背掉块及盆背侧和尾缘同时掉块的叶片建议不再使用。

转子叶顶间隙值及改型对压气机性能影响的数值模拟

为了分析转子叶顶间隙值和改型对压气机性能的影响,以典型轴流跨声速压气机NASA stage 35为对象,对不同叶顶间隙值的压气机进行数值模拟。结果表明:叶顶间隙增大并且泄漏流强度提高,会导致脱体激波位置前移,转子吸力面激波作用位置后移,前缘溢流现象减弱,叶尖泄漏涡与激波作用增强,间隙区域涡量增加,靠近前缘的涡核向下游移动,但附面层与激波之间的作用减弱;不同叶顶间隙值的压气机失速机制不同,在小间隙下压气机失速是由叶尖泄漏涡和转子吸力面附面层分离共同作用引起的,在大间隙下压气机失速是由叶尖泄漏涡引起的;在研究的变化范围内,叶顶间隙值为0.50τ时,压气机性能最好,峰值效率和稳定裕度分别提高了0.16%和2.39%;将最优间隙改型成平行扩张式和正弦波间隙后,压气机性能提高,脱体激波后移,叶尖泄漏涡与激波作用程度减弱,转子吸力面附面层分离减弱,改型间隙能够减少叶片制作材料,减轻发动机质量。

Numerical Investigations on the Steady and Unsteady Leakage Flow and Heat Transfer Characteristics of Rotor Blade Squealer Tip

The steady and unsteady leakage flow and heat transfer characteristics of the rotor blade squealer tip were conducted by solving Reynolds-Averaged Navier-Stokes （RANS） equations with k-co turbulence model. The first stage of GE-E3 engine with squealer tip in the rotor was adopted to perform this work. The tip clearance was set to be 1% of the rotor blade height and the groove depth was specified as 2% of the span. The results showed that there were two vortexes in the tip gap which determined the local heat transfer characteristics. In the steady flow field, the high heat transfer coefficient existed at several positions. In the unsteady case, the flow field in the squealer tip was mainly influenced by the upstream wake and the interaction of the blades potential fields. These unsteady effects induced the periodic variation of the leakage flow and the vortexes, which resulted in the fluctuation of the heat transfer coefficient. The largest fluctuation of the heat transfer coefficient on the surface of the groove bottom exceeded 16% of the averaged value on the surface of the squealer tip.