硅基内肋阵列微通道内的流动和换热特性

制作了四种带有圆柱形内肋阵列的硅基微通道,以去离子水为工质对其内部流动和换热特性进行了实验研究,并与平直微通道进行了对比,分析了内肋阵列微通道中流动阻力提升和强化换热的机理。研究表明;内肋阵列带来较大阻力的同时也极大地改善了换热;流体流经内肋阵列微通道时,其阻力在低Re数下主要来自壁面效应产生的摩擦阻力,高Re数下则受绕肋产生尾涡的影响较大;不同内肋布置方式对流体流动和换热影响显著,叉排布置比顺排布置的内肋阵列微通道具有更大的摩擦因子和换热系数,且增大垂直于流动方向内肋密度更有利于增强换热;内肋排列最为紧密的微通道#2综合换热性能最好,相同泵功下,其换热热阻相对于平直微通道降低了53.4%。     

楔形通道换热三维数值模拟

对涡轮叶片尾缘针肋通道的换热进行了数值模拟研究。为了研究冷却叶片尾缘处正压面与背压面楔角对换热和流动的影响,在Re=1.0×104-1.0×105进行了稳态湍流三维数值模拟;为了研究冷却叶片尾缘扰流柱上下两部分在流动方向错位的距离对通道传热和流动的影响,在针肋顺排及Re=2.0×104的情况下进行了稳态湍流三维数值模拟。得出了平行通道最宜被采用以及针肋错位通道中随着针肋错位距离的增加通道的换热和压力损失都增加的结论。     

不同孔隙率圆形微针肋热沉流动及传热特性

本文利用CFD数值模拟软件对当量直径为200μm的不同孔隙率的叉排圆形微针肋热沉的流动和传热特性进行了数值模拟。模拟结果表明,随着雷诺数的增加,针肋尾部出现不同形态的涡。不同孔隙率的通道中,由于后排针肋的影响,针肋尾迹区的涡的形态、大小出现不同。对不同孔隙率的微针肋热沉,热流密度的变化对热沉的努塞尔数Nu的影响不同,孔隙率较小时热流密度对热沉的努塞尔数Nu影响不大,孔隙率较大时热流密度升高,热沉的努塞尔数Nu升高。     

振荡流热管换热器的数值模拟及场协同分析

振荡流热管是一种新型高效传热元件,本文采用数值模拟的方法研究了振荡流热管换热器内的流动与换热情况,并结合场协同理论分析了换热器内管子排列方式、热风进口温度和进口流量对振荡流热管换热器换热情况的影响。模拟结果显示,换热器内管子叉排排列方式的换热效果优于顺排方式,热风进口流量对换热器内温差场均匀性影响较大,而热风进口温度对温差场均匀性影响较小。这些结果对振荡流热管换热器的设计具有一定的指导意义。     

涡轮叶片不同肋倾角交错肋冷却流动与传热研究

交错肋是航空发动机涡轮叶片的一种高性能内冷结构,为研究涡轮叶片内部交错肋冷却结构的流动和传热特性,针对30?、35?和45?三种肋倾角的交错肋结构进行了雷诺数在17000～70000之间的稳态传热实验和数值模拟研究。数值计算的有效性通过与实验结果进行对比得到充分验证。实验结果显示,在子通道个数和雷诺数均相同的情况下,平均Nu数和摩擦因子均随肋倾角的增大而增加;对比30?倾角的交错肋结构,45?倾角交错肋结构的平均Nu数增加了40.7%,摩擦因子增加了204.9%,综合传热性能提升了13.4%。数值计算结果显示,肋倾角的增大不仅增强了转向区域的冲击作用,而且加强了对侧子通道间的流动掺混,从而达到强化传热的效果。     

肋片间距对环形通道流动和换热的影响

本文用稳态层流模型对几种具有不同肋片间距的环型通道内的流动和换热进行了数值模拟.计算结果表明:长直肋片截断后,流动和换热沿长度方向具有周期性的入口段效应,从而增强了换热.与长直肋片通道相比,βL=13/7时,换热增强了27%,而阻力仅增加6.8%.对于带肋环形通道,Re数增大,换热增强.     

涡轮叶片冷却通道高性能微小肋湍流传热的数值研究

为了提高涡轮叶片内冷通道的换热性能,针对分别带有直肋、斜肋、V肋和W肋这四种微小结构肋的冷却通道进行了数值计算并。通道宽高比为6,肋间距与肋高比为10,肋高与水力直径比为0.029。采用低雷诺数AKN k-ε模型研究了雷诺数范围从36700到60000时四种带肋通道的换热与流动特性并与实验结果相比较,发现通道换热性能和压力损失与稳态实验结果较一致。研究表明,W肋换热性能最优,其平均努塞尔数是流动充分发展的光滑通道的2.2到2.4倍,摩擦因子是光滑通道的3.7～4.0倍。其次是V肋、直肋,斜肋最低。分析流场发现直肋下游回流区最大,壁面努塞尔数在横向上较均匀,而斜肋、V肋和W肋因为二次流的存在回流区较小,壁面努塞尔数沿着肋展方向降低。     

燃机叶片平行肋扰流内冷通道传热特性研究Part2:耦合传热特性

平行肋扰流通道是高温透平叶片常用的冷却结构。本文通过批量(约1000次)的气热耦合数值计算对不同几何结构平行肋扰流冷却通道的流动与耦合传热特性进行研究.对于固定压差通道,存在使固体外壁温度最低的肋片布置形式及对应的最优冷气量,针对某重型燃机动叶设计了不同肋片角度的平行肋扰流冷却通道并进行了气热耦合数值计算,表明60°肋能在最小的冷气量下取得最强的换热,验证了机理研究的结论.     

基于微小通道尺度效应的冷板沸腾换热数值研究

选用R134a、R123、水三种不同的介质,分别对不同流速和不同通道尺寸下微小通道冷板的流动沸腾换热进行数值模拟研究,分析了介质、流速及通道尺寸对换热器流动沸腾换热性能的影响。研究发现:微小通道冷板的通道宽度为1mm时,采用8mm的通道肋高和低流速的R134a介质,既能控制加热表面温升,又能有效地将利用介质的沸腾换热和流动换热。     

仿螺旋肋片道流动换热特性的数值研究

运用数值计算的方法对仿螺旋肋片内冷通道内的流动特性和传热特性进行了研究,共建立五组模型,分析了入口冷气雷诺数和肋片排布方式对壁面换热和通道阻力特性的影响规律.研究结果表明:(1)随着肋片与主流方向的夹角α的增大,壁面换热增强,同时通道内平均阻力系数显著增大.(2)随着入口冷气雷诺数的增大,壁面平均努塞尔数Nu增大,平均阻力系数Eu减小.(3)改变肋片倾斜角β可使综合性能提高,且存在最佳值.在研究范围内,α=15°,β=15°时综合性能最好.     

Comparisons of Heat Transfer Enhancement of an Internal Blade Tip with Metal or Insulating Pins

Cooling methods are needed for turbine blade tips to ensure a long durability and safe operation. A common way to cool a tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement like flow. Improved internal convective cooling is therefore required to increase the blade tip lifetime. In the present study, augmented heat transfer of an internal blade tip with pin-fin arrays has been investigated numerically using a conjugate heat transfer method. The computational domain includes the fluid region and the solid pins as well as the tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The main objective of the present study is to observe the effect of the pin material on heat transfer enhancement of the pin-finned tips. It is found that due to the combination of turning, impingement and pin-fin crossflow, the heat transfer coefficient of a pin-finned tip is a factor of 2.9 higher than that of a smooth tip at the cost of an increased pressure drop by less than 10%. The usage of metal pins can reduce the tip temperature effectively and thereby remove the heat load from the tip. Also, it is found that the tip heat transfer is enhanced even by using insulating pins having low thermal conductivity at low Reynolds numbers. The comparisons of overall performances are also included.     

高温涡轮叶片三种内冷通道冷却性能的实验研究

本文用实验方法研究了高温涡轮叶片三种内冷通道的压力分布、冷热态流阻及局部换热系数分布．叶片前部分别采用径向光滑通道、集中冲击冷却和分散冲击冷却三种结构，叶片后部则分别采用三排φ3扰流柱和五排φ2扰流柱稠密布置两种结构．对这三种结构进行了冷却性能比较，提出了该类冷却通道的最佳结构．     

Experiments on the unsteady flow field and noise generation in a centrifugal pump impeller

This paper reports on an experimental investigation of large-scale flowfield instabilities in a pump rotor and the process of noise generation by these instabilities. Measurements of the fluctuating components of velocity and surface pressure were made with hot-wire probes and surface mounted pressure transducers on a seven bladed back swept centrifugal water pump impeller operating with air as the working fluid. The impeller was operated without a volute or scroll diffuser, thereby eliminating any sound generation from pressure fluctuations on the volute cutoff. Thus the study focused on flow field and noise components other than the blade passage frequency (and its harmonics). The primary goal of the study was to provide fundamental information on the unsteady flow processes, particularly those associated with the noise generation in the device. It was further anticipated that detailed flow measurements would be useful for the validation of future computational simulations.The measured data at the discharge show a jet-wake type of flow pattern which results in a strong vorticity field. The flow with high velocity found on the pressure side of the impeller tends to move to the low-pressure region present at the suction side of the passage as a form of roll-up around the blade trailing edge. This motion causes an unsteady flow separation at the suction side of the blade and consequently disturbs the flow in the adjacent passage. By interacting with the impeller blades near the trailing edges, this instability flow causes a periodic pressure fluctuation on the blade surface and generates noise by a trailing edge generation mechanism. The spectrum of surface pressure measured at the trailing edge of each blade reveals a cluster of peaks which were identified with azimuthal mode numbers. The correlation between the acoustic farfield pressure and the surface pressure on the impeller blade has proven that the azimuthal modes synchronized with the number of impeller blades generate noise much more efficiently than the other modes. The paper also clarifies the correlation between unsteady flowfield measurements, in both impeller and laboratory co-ordinates, with the radiated noise properties. Thus some light is shed on the noise generation mechanisms of this particular device.     

Experimental Study of Flow Through a Blade Trailing Edge with a Wavy Partition

Abstract

Flow through a blade trailing edge passage has been experimentally investigated in this article. This rectangular passage is divided into two channels by either a straight or a 120° wavy partition. Fluid in the first channel was injected into the second channel via 14 openings (holes) distributed uniformly and in the crests and troughs for the wavy configuration. Particle image velocimetry and a charge coupled device camera were used in experiment, with Reynolds number varying from 1,800 to 6,700. Experimental results show that the wavy configuration produces an oscillation flow in the second channel. The cause for the oscillation may due to the 120° wavy partition causing shear-layer instabilities and the formation of spanwise eddies by the wavy board. Pictures from the charge coupled device camera revealed strong mixing in the trailing edge, and this mixing could enhance heat transfer, which was confirmed in previous research. The amplitude of oscillation depends on Reynolds number and hole positions. It was observed that the injection flow was not symmetric to the openings, and it was skewed to the direction of the first channel main flow. The ratio of flow rate through the outlet and the bleeding holes was from 1:1 to 1:3.     

空调风机叶道内旋涡流动分析及进气口偏心的影响

本文采用CFD方法,详细分析了空调用多翼离心风机叶道中的气流分布以及进气口偏心的影响。研究表明,风机叶道内存在大范围的气流分离现象。在后盘附近,存在分离现象的叶道约占2/3,主要分布在蜗壳内侧;而在“前盘”附近,几乎所有叶道都存在分离现象。在“前盘”附近,蜗舌下方的叶道中气流几乎停滞,蜗舌下游叶道为回流和尾缘旋涡所充满,至临近蜗壳出口侧,前缘旋涡逐步形成、发展并融合尾缘旋涡,最后衰减、消失。风机进气口向蜗壳内侧偏置适当距离, “前盘”附近叶道旋涡分布范围明显减小。     

Visualization of aerodynamic noise source around a rotating fan blade

The purpose of this study is to understand the aerodynamic noise source distribution around a rotating fan blade by measuring the noise signal and velocity field around the blade. The local noise-level distribution over the fan blade is measured by microphone arrays, and the flow field is visualized by smoke and phase-averaged PIV measurement. The noise source distribution is examined by cross-correlation analysis between noise signal and velocity fluctuation. It is found that the noise source is located near the rotating fan blade, especially around leading and trailing edges. The separation and reattachment of flow are observed near the leading edge, and the tip vortices and vortex shedding are found near the trailing edge. The cross-correlation distribution of the noise signal and the radial velocity fluctuation shows large magnitude in the correlated regions, which indicates the noise generation by the formation of vortex structure around the blade.     

缝隙抽吸对液膜撕裂特性影响的试验研究

本文在空气-水膜两相流动试验装置上,利用高速摄影机对空心静叶缝隙抽吸下的静叶出口边液膜撕裂特性进行了试验研究,结果表明:缝隙抽吸可以将静叶表面上的大部分流动液膜去除掉,水份在叶片出口边之前形不成完整的流动液膜,仅表现为溪状流动,静叶出口边的撕裂形式主要为丝线状撕裂,撕裂形成的水滴数目和直径将明显地减小。     

前缘弯掠斜流转子叶顶间隙流动特性数值分析

本文对前缘弯掠斜流转子叶顶间隙内的流动特性进行了数值分析。结果表明:叶顶间隙气流与主流发生卷吸而生成泄漏涡。泄漏涡作用的区域具有较低的压力分布。在叶片通道内,泄漏涡沿着与转子旋向相反的方向朝相邻叶片的压力面移动。大间隙时的泄漏涡比小间隙时强烈。低流量时泄漏涡的作用区域比高流量时大。在各种流量特性下,叶顶尾缘近吸力面区域都存在着二次间隙流。     

Local Heat Transfer Distribution in a Rectangular Pin Channel With and Without Vortex Generators

Short pin fins are used to enhance heat transfer rates by increasing the level of turbulence in the trailing edge of gas turbine blades. Experiments are conducted to investigate the local Nusselt number distributions in a staggered pin-fin array using the infrared thermal imaging technique. The pin fins are arranged in a rectangular channel with an aspect ratio of 9. The pins have streamwise pitch-to-diameter (X_S/D) and spanwise pitch-to-diameter (X_T/D) ratios of 2 with a pin height-to-diameter (H/D) ratio of 2. Ejection holes of 5-mm diameter with a pitch of 12.7 mm are used to study the effects of lateral ejection. Both one-wall and two-wall heating situations are studied for straight-flow and lateral-ejection cases. It is found that the local Nusselt numbers are highest below the horseshoe vortices just upstream of the individual pin fins. For the straight-flow case, the Nusselt numbers for the two-wall heating case are observed to be 15–20% higher than those of the one-wall heating case. Lateral ejection causes a decrease of about 1–10% for the one-wall heating case, while there is an increase of about 10% for the two-wall heating case. Experiments are also carried out with vortex generators between individual pin fins. Vortex generators cause an increase in heat transfer by about 50% compared to the straight-flow cases.     

Computation of leading edge film cooling from a CONSOLE geometry (CONverging Slot hOLE)

The aim of this study is to investigate the effect of mass flow rate on film cooling effectiveness and heat transfer over a gas turbine rotor blade with three staggered rows of shower-head holes which are inclined at 30° to the spanwise direction, and are normal to the streamwise direction on the blade. To improve film cooling effectiveness, the standard cylindrical holes, located on the leading edge region, are replaced with the converging slot holes (console). The ANSYS CFX has been used for this computational simulation. The turbulence is approximated by a k-ε model. Detailed film effectiveness distributions are presented for different mass flow rate. The numerical results are compared with experimental data.