壁冷叶片冲击射流孔的流动特性实验研究

用实验的方法对涡轮叶片壁面冲击冷却的流动特性进行了研究，并用直头五孔探针对冲击射流孔内的流场进行了详细的测量，着重研究了不同雷诺数和不同的通道高度比（通道高度与射流孔直径之比z／d）对射流孔内流动结构和流量系数的影响。实验结果表明：通道高度的变化会明显改变孔内的流场结构和孔的流量系数；而在同一通道高度下，雷诺数的改变对孔内流场影响相对较小。在射流孔内存在着漩涡结构，这有助于深入了解气膜冷却的内在机理。     

微引射式防冰腔结构参数对换热性能的影响

采用数值模拟的方法研究了航空发动机微引射式防冰腔结构参数对防冰热效率和发动机蒙皮温度分布的影响.通过改变射流孔直径、射流孔孔距、混合腔长径比和波纹板通道出口高度,建立了不同的微引射式防冰腔模型.在进口热气流量一致的情况下,对不同防冰腔模型进行了数值计算.结果表明:减小射流孔直径和波纹板通道出口截面高度能提高防冰热效率和...     

涡轮工作叶片内冷通道换热特性数值模拟

采用非结构化网格和SST紊流模型,求解三维N-S方程,对带90°肋和气膜孔的矩形通道在入口雷诺数60000,罗斯贝数0.11,气膜孔总出流比为0.22时的三维流场进行了数值模拟。分析了通道旋转和静止时各个面的换热变化规律。结果表明,通道静止时,不但布置了粗糙肋的上、下壁面换热得到了增强,光滑的侧壁换热同样获得了增强;通道旋转时流场更加复杂,旋转所产生的二次流动使各个壁面的换热进一步增强。     

孔板支撑换热器壳程流场的数值预测

孔板支撑换热器用整圆形孔板代替传统的弓形折流板来支撑管束，消除了大部分传热死区，并由于小孔射流和扰流作用在较低雷诺数下提高了传热效率。本文提出了孔板支撑换热器的单元流道简化模型，用数值方法预测了大管孔孔板和小圆孔孔板支撑单元流道的流场。结果证明孔板支撑强化传热的主要机理是破坏管壁表面的液体边界层，大管孔孔板的综合性能优于小圆孔孔板。     

带侧向出流孔的梯形通道内部换热特性数值研究

采用非结构化网格和标准k-ε湍流模型,求解三雏N-S方程,对带侧向出流孔的梯形通道内表面流动情况进行了数值模拟,具体研究了孔径为0.03,通道进口雷诺数为30000,测流比分别等于1,0.3,0时梯形通道内的流动及换热情况.结果表明:随着侧流比的减小,通道内表面沿流向相同位置换热趋于一致;平均努赛尔数随之单调递增.     

排尘孔涡轮冷却叶片叶顶流动与传热研究

涡轮叶片叶顶排尘孔用于清除冷气中掺杂的尘粒,以保证气膜孔和冲击孔的可靠工作,但排尘孔射流引起叶顶流动和传热问题。采用参数化方法建立有、无排尘孔涡轮冷却叶片几何模型,基于包含叶片主体、主燃气通道和三腔回流式内冷却通道的全局模型,采用流热耦合数值分析,开展排尘孔对涡轮冷却叶片叶顶流动与传热问题的初步研究。研究结果表明,对比有、无排尘孔叶片,排尘孔射流可降低叶顶平均温度约25 K;冷却通道对流换热作用和叶顶排尘孔射流可使叶顶平面降温400～600 K,冷却效果与冷却通道冷气流量和尘孔结构在叶顶位置相关;排尘孔叶顶射流对叶顶间隙高温燃气泄漏具有阻碍作用,可以提高叶片总压恢复系数约0.5%～1.5%,随着冷气流量的增大,这种作用增强;尘孔结构设计应兼顾射流对叶顶流动与传热的共同影响。     

带顶部出流孔U型通道的流阻与换热研究

内冷通道与叶尖冷却均匀是保障燃气轮机涡轮叶片安全稳定运行的关键技术,带顶端出流孔的U型通道作为这两个冷却技术相结合的产物,极具研究价值.为分析单个顶端出流孔的不同空间位置对U型通道流动换热特性的影响,采用数值仿真的方法展开研究.研究结果显示:当顶端出流孔处于通道回转段出口侧时,流动性能下降了约15％,但换热系数显著提高,综合热性能系数提升了6％.     

主燃孔方案对回流燃烧室流动影响的数值研究

为探究主燃孔开孔方案对辅助动力装置回流燃烧室流动特性的影响,开展5种主燃孔开孔方案的矩形回流燃烧室冷态流场数值模拟研究,数值模拟方法通过粒子图像测速试验数据进行了有效性验证。结果表明：燃烧室主燃区流场形成了大尺度双涡流动结构,有利于火焰稳定。外环主燃孔射流穿透深度明显大于内环主燃孔射流,因此对流场影响更大。外环主燃孔数目越多,孔径越小,主燃区沿轴向和展向的尺寸都变大。主燃孔排列方式对主燃区流场结构影响很小,但对中间区流场影响显著。     

微尺度受限冲击冷却通道换热特性研究

为了更进一步研究真实发动机尺寸下冲击通道的流动与换热情况,针对冲击孔与气膜孔组合形式的受限冲击通道,在保证与真实发动机工况相等的克努森数,通过实验研究与数值模拟研究,进一步解释了不同结构微小冲击通道的整体换热情况,结果表明,在相同的雷诺数下,冲击射流孔径越小,冲击靶面驻点区域内换热越强,冲击平均对流换热系数越大。孔间距越小,冲击靶面平均对流换热系数越大,并且随着射流冲击距的增大,换热减弱。     

基于CFD的射流曝气器关键结构参数研究

运用CFD方法对单级单喷嘴自吸式曝气器进行数值模拟,通过改变影响射流曝气器充氧能力的结构参数,获得了射流曝气器内部流场的流态情况,反映了不同结构参数对其充氧能力的影响,并获得了具有较好充氧能力射流曝气器关键结构参数。     

A numerical study of impingement heat transfer in a confined circular jet

Heat transfer characteristics of a submerged circular jet impingement with a confined plate was studied numerically. The continuity, momentum and energy equations were solved simultaneously. FIDAP, a finite element code, was used to formulate and solve the matrix equations for fluid elements. The effects of channel height and Reynolds number on the local Nusselt number were considered in the range of H=0.5–1.5 and Re=100–900, respectively. It was found that the channel height influenced strongly on the surface temperature, shear stress and pressure drop. The peak temperature was observed and gradually moved outward to the rim of the heated circular plate with increasing the Reynolds number, which may be related to flow recirculation region in the channel. It is also noted that the pressure drop increased more than the average heat transfer coefficient as the Reynolds number increased. For Pr=7, the Nusselt number was much more dependent on the Reynolds number than the channel height, and the magnitude of the second peak in the Nusselt number distribution increased as the Reynolds number increased. The local Nusselt number calculated based on a mixing-cup temperature was considerably different from that using the inlet nozzle temperature for H=0.5 and Re=100. The present study showed that the local Nusselt number of a confined submerged jet was significantly larger than that of the unconfined free jet which was available in the literature.     

An experimented study on the flow characteristics in a three-dimensional cylindrical branching channel

In this paper, we report on an experimented study on incompressible Newtonian flow in a three-dimensional cylindrical branching channel. The flow configuration studied in the present investigation is such that a fully developed laminar flow enters an abruptly expanded cylinder and the flow leaves this cylinder by two identical cylindrical outlet branch pipes. Representative velocities in the flow field were recorded by LDV (Laser Doppler Velocimetry) measurements, and volume flow rate from each outlet branch pipe was measured. Flow visualization in representative symmetric planes was also carried out. Based on results of the present investigation, the flow field in the three-dimensional cylindrical branching channel was clarified within the range of laminar flow. The characteristics of the branch flow rate were obtained and showed that there exist two distinct domains of strong asymmetric flow distribution from the outlet branch pipes, depending upon Reynolds numbers. It was further observed that the flow became time periodic as the Reynolds number was increased.     

基于自激振荡脉冲效应的雾化喷嘴出口流道空化特性研究

喷嘴结构及射流运动参数对液体空化流动状态有重要影响。基于空化泡溃灭的雾化机理和自激振荡脉冲喷嘴出口流道空化过程,分析空化效应对自激振荡脉冲射流雾化效果的影响。依据自激振荡脉冲雾化喷嘴结构,分析射流来流速度和脉动压力对喷嘴出口流道空化效应的影响,提出利用来流雷诺数和脉动特征值表征喷嘴出口流道空化程度,并根据自激振荡脉冲喷嘴有限元分析得到喷嘴出口流道较好空化状态的来流雷诺数和喷嘴腔室长径比。研究结果表明:当来流雷诺数在2.14×10~5~3.05×10~5内逐渐增大时,自激振荡脉冲雾化喷嘴出口流道液相体积分数先减小后增大,相应的空化程度先增大后减小。雷诺数在2.44×10~5~2.75×10~5内可以使喷嘴出口流道形成较好空化效应,尤其在2.44×10~5附近时喷嘴出口流道出现最好的空化状态;脉动特征值与喷嘴出口流道处脉动压力幅值差成正比,随着自激振荡脉冲雾化喷嘴腔室长径比增大,脉动压力幅值差值先减小后增大。当喷嘴腔室长径比为0.60~0.70时,喷嘴出口流道空化状态较好。计算结果为自激振荡脉冲射流雾化喷嘴设计提供了理论依据。     

PIV measurements in a turbulent wall jet over a backward-facing step in a three-dimensional,non-confined channel

A study of a turbulent wall jet over a backward-facing step is especially of interest because it shows a rich phenomenon flow and a mechanism to alter the flow characteristics downstream of the step. However, studies on this flow configuration are rare. In this paper, we considered this flow configuration in a non-confined channel as the specific engineering applications of electrical rotating machines and alternator that can be found in modern wind generators of the power production industry and automobile engines. The turbulent wall jet over a backward-facing step in a non-confined wind tunnel had the jet Reynolds number of 24,100 and the step Reynolds number of 11,900. Particle image velocity (PIV) and stereoscopic PIV measurements were performed along the central plane and several cross-stream planes. Numerical simulation of the test configuration was conducted by solving the three-dimensional Reynolds Averaged Navier–Stokes (RANS) equations with the second-order closure Reynolds stress model (RSM). The mean flow fields and second-order statistical moments from the RSM simulation were compared to results that were obtained through the PIV and stereo-PIV experiments. The mean reattachment length obtained from the current configuration was much shorter than those from the backward-facing step in the plane channel. The stereo-PIV measurements in the cross-stream planes revealed a high three-dimensionality of the flow, a high population of streamwise vortice in the upper region, near the side walls and the corners formed by the side walls and the bottom wall. The obtained results also confirmed the presence of the wall-jet formation on the bottom wall.     

壁面粗糙度效应对微流体流动特性的影响

壁面粗糙度对微流道流动特性有重要影响。分别用矩形、三角形和圆顶形粗糙元对壁面粗糙度进行模拟,详细讨论了雷诺数、粗糙元高度、粗糙元间距等因素对流速、压降及流动阻力的影响。结果表明:与光滑流道相比,粗糙度使壁面附近的流动发生明显改变,从而导致微流道内流速、压降及流阻高于经典理论预测值;微流道内流动阻力随着雷诺数及粗糙元高度的增大而增大,而随着粗糙元间距的增大,流动阻力逐渐减小。三种粗糙元相比,矩形粗糙元的影响最大,圆顶形次之,而三角形粗糙元的影响最小,可见在实际应用场合,确立合适的粗糙元形状对分析结果非常重要。     

BTA深孔钻射流孔参数的优化与仿真

针对射流孔几何参数对BTA深孔钻喉部流场的影响,对射流孔直径、角度与射流孔距离喉部的位置进行有限元数值模拟,提出一种最优的新型喉部结构。在设置有限元模型的湍流强度和耗散率基础上,进行不同几何参数的深孔钻头喉部结构的排屑能力对比试验,测量冷却液系统的冷却液出口断面流出平均速度。试验结果表明:最优喉部结构为∅38mm BTA深孔钻头所组成的冷却系统,冷却液出口断面流出的平均速度提高9.6%,同时提高了冷却液系统整体的排屑能力。由相似定理得出,冷却液系统的排屑能力提高9.6%。     

Heat transfer characteristics of gaseous slip flow in a micro-channel

Two-dimensional compressible momentum and energy equations with slip boundary conditions are solved to obtain the heat transfer characteristics of gaseous slip flow in a micro-channel with CWT (constant wall temperature) whose temperature is lower or higher than the inlet temperature (cooled case or heated case). The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The stagnation temperature is fixed at 300 K and the computations were done for the wall temperature which ranges from 250 K to 350 K. The channel height ranges from 2 to 10 μm and the channel aspect ratio is 200. The stagnation pressure is chosen in such a way that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure is fixed at atmospheric condition. The bulk temperature and the total temperature of the heated case are compared with those of the cooled case and also compared with temperatures of the incompressible flow in a conventional sized channel. Heat transfer characteristics of the gaseous flow are different from those of the liquid flow. And they are also different from each cooled and heated case. A correlation for the prediction of the heat transfer rate of the gaseous slip flow in a micro-channel is proposed.     

刀尖角容腔对直角转弯流道液流特性影响的PIV试验研究

针对液压集成块典型的直角转弯流道结构,搭建了一个低速流场可视化测量试验台,采用2D-PIV流场测试技术实现了6种带有不同刀尖角容腔的直角转弯流道流场的测量。测量结果表明：在刀尖角容腔和直角转弯出流管段内拐角处分别出现涡流,前者涡流尺度随容腔长度的增加而增大,后者涡流尺度则与容腔长度无关。分析了刀尖角容腔长度及与进出口相对位置的关系对直角转弯流道液流特性的影响,发现出流方向正对刀尖角容腔时的流动损失更小。研究结果为集成块内部转弯流道结构优化提供了设计参考。