共查询到20条相似文献,搜索用时 418 毫秒
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准确分析和控制射流冲击对航母甲板环境的影响是新型喷气偏流板设计和布局的关键所在。为了确定射流冲击影响最小的偏流板布局,运用有限体积法,采用分区混合网格方案,结合雷诺时均纳维斯托克斯(RANS)方程和SST k-ω湍流模型对喷气偏流板在不同布局下的射流冲击效应进行三维数值模拟。选取舰载机双发动机全加力状态时喷气偏流板与发动机距离不同、喷气偏流板倾角不同共12种布局组合进行射流冲击效应的对比计算,计算结果显示了喷气偏流板各布局下的流场参数、传热特性、尾喷口温升、冲击力和力矩等分布规律。定性和定量分析了燃气射流冲击下温度场和速度场的危险区域,结果表明,偏流板与发动机距离5 m、偏流板倾角45°时的布局更有利于将燃气射流向上引导。在此基础上,基于倾角最小化原则及二次导流原理优化设计了一种导流隔热性能好、工作稳定性高的被动隔热式喷气偏流板装置。 相似文献
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采用经过实验验证的数值模型研究了周期性射流冲击下的流场对传热强化的影响。根据不同波形(正弦波、三角形波和矩形波)规律变化的射流对平板的冲击会产生不同的传热特性,研究得到了滞止点处的温度、传热系数和湍流强度随时间变化的规律。研究结果表明:当正弦波射流、三角形波射流的信号处于上升阶段时,湍流强度在稍有延迟后会产生一个瞬时的增强,可对强化传热起到促进作用,但在它们随后的波形变化中湍流强度仅有缓慢的升降,矩形波射流在信号发生阶跃变化时,会产生湍流强度的脉冲增强,尤其是在信号跃降时产生的瞬时脉冲增强比信号跃升时产生的脉冲增强更大,可有效强化传热;远离滞止点的流场的周期性波动仍然存在,但幅值大大减小,矩形波射流的平均速度大于其他波形射流的速度。 相似文献
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后向台阶绕流是包含丰富流动现象的典型分离再附流动,在工程中应用广泛。这里针对过渡流下后向台阶绕流低频脉动特性对传热的影响展开研究,重点分析了主回流区再附着点下游传热得到强化的原因。结果表明:过渡流下的低频脉动特性诱导流动在壁面附近形成旋涡,这些旋涡的运动破坏了速度边界层的均匀发展,同时加强了冷热流体的混合,从而强化了底面传热,再附着点下游局部区域的传热比层流时提升了3倍以上。随着雷诺数的继续增大,近壁旋涡的形态发生变化,促使流体冲击壁面的角度增大,低速回流范围减小,从而进一步强化了底面传热。 相似文献
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蜂窝式除湿转轮的传热传质数学模型及其试验验证 总被引:1,自引:1,他引:0
针对蜂窝式除湿转轮的结构特点以及波纹形通道的传热传质特性,建立了转轮除湿过程中的传热传质数学模型,用试验数据验证了其合理性。分析和讨论了传热传质过程中空气温湿度和干燥剂温度及其含水量的分布情况和特征。数值计算发现:在波纹形通道内沿再生空气方向存在一条空气含湿量峰值线,该峰值线向出口方向的迁移时间和峰值的大小决定了再生速度和再生效率。为了提高再生效率,应该尽可能加快再生空气含湿峰值向出口处的移动过程,提高其迁移速度,降低迁移时间。最后还对运行参数对再生空气出口含湿峰值的大小及其迁移时间的影响进行了讨论。 相似文献
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研究了复合台阶绕流中典型旋涡和壁面传热之间的关联性机理。通过PIV实验对所用的数值模拟方法进行了验证。从瞬态和时均两方面分析了早期过渡流区域复合台阶绕流的传热特性。结果表明:从层流到早期过渡流壁面的时均传热随雷诺数呈现出非线性的增长趋势,同时台阶底面局部区域的流动传热出现了非相似性。为了理清上述传热特征的形成原因,对一个振动周期里典型旋涡的形态特征和演变规律进行了分析,发现旋涡再附着冲击角γ,近壁冲击流速Ω和旋涡流向长度Lv是影响传热的三个关键因素。一般情况下,壁面传热随着γ和Ω的增大而增大。 相似文献
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通过引入冲蚀数的概念来描述磨料射流切割所需的最小能量。从牛顿定律和赫兹方程导出一个量纲一的量,称为相对冲蚀强度,发现在磨料冲击韧度材料过程中保持不变。进而基于多相流动力学模型计算出磨料速度,模型中特别考虑了形成磨料射流的关键元件混合管中空气流量对磨料加速过程的影响。最后建立了具有空气流量调节装置的试验系统来测量冲蚀数,表明它可以应用于预测磨料射流切割性能。 相似文献
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Makatar Wae-hayee Perapong Tekasakul Smith Eiamsa-ard Chayut Nuntadusit 《Journal of Mechanical Science and Technology》2014,28(7):2909-2917
An effect of cross-flow velocity on flow and heat transfer characteristics of impinging jet in the case of low jet-to-plate distance at H = 2D was experimentally and numerically investigated. In the experiments, the air jet from orifice impingement on the wall of wind tunnel while a cross-flow was simultaneously induced normal to the jet flow. The jet velocity was fixed while the cross-flow velocity was varied corresponding to velocity ratios (jet velocity/cross-flow velocity) VR = 3, 5 and 7. The temperature distribution on an impinged surface was visualized by using thermochromic liquid crystal sheet (TLCs), and Nusselt number distribution was evaluated by using image processing method. The flow pattern on impingement surface was visualized by using oil film technique. The numerical simulation was carried out for a better understanding of the jet flow in the cross-flow. The results show that Nusselt number peak shifts downstream and the Nusselt number peak increases with increasing cross-flow velocity. 相似文献
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Qing-Yang Zhao Heeyoon Chung Seok Min Choi Hyung Hee Cho 《Journal of Mechanical Science and Technology》2016,30(2):525-531
The characteristics of fluid flow and heat transfer, which are affected by the guide wall in a jet impinged leading edge channel, have been investigated numerically using three-dimensional Reynolds-averaged Navier–Stokes analysis via the shear stress transport turbulence model and gamma theta transitional turbulence model. A constant wall heat flux condition has been applied to the leading edge surface. The jet-to-surface distance is constant, which is three times that of the jet diameter. The arrangement of the guide wall near the jet hole is set as a variable. Results presented in this study include the Nusselt number contour, velocity vector, streamline with velocity, and local Nusselt number distribution along the central line on the leading edge surface. The average Nusselt number and average pressure loss between jet nozzle and channel exit are calculated to assess the thermal performance. The application of the guide wall is aimed at improving heat transfer uniformity on the leading edge surface. Results indicated that the streamwise guide wall ensures the vertical jet impingement flow intensity and prevents the flow after impingement to reflux into jet flow. Thus, a combined rectangular guide wall benefits the average heat transfer, thermal performance and heat transfer distribution uniformity. 相似文献
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Koonlaya Kanokjaruvijit Chakkraphan Thawonngamyingsakul Somchai Wongwises 《Journal of Mechanical Science and Technology》2010,24(9):1809-1818
The purpose of this study is to numerically investigate heat transfer and flow field in a semi-confined axi-symmetric laminar
air jet impinging on a concave surface, or dimple, with uniform heat flux. A commercial software package relying on the finite
element method was used for the simulation, and mesh convergence was examined in order to minimize computational cost. Jet
impingement on a flat plate was used as a baseline reference case, and flat plate results were validated against previously
published experimental data with good agreement. The effects of various parameters involved in dimple impingement -such as
Reynolds number (Re) between 100–1,400; jet-to-plate spacing (H/Dj) ranging from 2 to 6 jet diameters; dimple depths (d/Dd) of 0.1, 0.15, and 0.2; and the ratio of jet diameter and dimple projected diameter (Dj/Dd) from 0.25 to 1—were all studied. Comparisons show that heat transfer reduction occurs in the presence of dimples because
of the larger impingement area, which results in less momentum flux. The dimple curvature lifts the post-impinging fluid and
creates a backflow, instead of allowing it to maintain contact with the surface, as is the case with flat plate impingement. 相似文献
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Kui-Soon Kim 《Journal of Mechanical Science and Technology》1993,7(3):258-271
The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy. 相似文献
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《风机技术》2021,(1)
The flame temperature in the combustor of a gas turbine is usually as high as 2000 K, while the maximum temperature that can be endured by metal materials is less than 1200 K at present. Therefore, various protective and cooling measures are needed to ensure the operation life of the liner wall which wraps the flame. The lean premixed combustor can meet the increasingly stringent emission requirements, but it requires more air for premixed combustion and then less air for cooling and dilution. In order to obtain a better impingement jet cooling structure, this paper studied the impingement jet cooling structure with vertical circular holes of equal diameter under single outlet condition. The structural variables studied include the jet hole diameter D, the impinging distance Z, the jet hole length(jet plate thickness) t, and the jet-to-jet spacing X is ignored. Among them, X/D(the ratio of the jet-to-jet spacing to the jet diameter) is inversely correlated with the mass flow rate. Within the constant X/D being equal to 10, the influence of D, Z and t on the average heat transfer coefficient h of the target surface under same mass flow was determined by means of conjugate numerical heat transfer analysis and orthogonal test. The results show that Z has significant influence on h, D has moderate influence on h, and t has negligible influence on h. Further, by means of regression orthogonal test, the influence trend of parameters Z and D on h at X/D=10 was studied. The optimal values of Z and D within the research scope were found. 相似文献
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近距离下淹没冲击射流具有重要的应用前景,但有关其动态流场特性的研究尚不充分。利用粒子图像测速技术(Particle image velocimetry,PIV)对冲击距离为H/D=1时的动态流场特性进行测量,研究雷诺数Re和喷嘴端面轮廓(壁面约束)对间隙内旋涡生成的影响,并对试验数据进行涡量分析与本征正交分解方法(Proper orthogonal decomposition,POD)分析。结果表明,雷诺数Re对不同喷嘴端面轮廓(壁面约束)的旋涡生成和迁移影响规律不同。雷诺数对直角型喷嘴的双涡环模式流态影响较小,但对圆角型喷嘴卷吸流态影响较大,且随雷诺数的增大流场出现动态对称涡旋,该对称涡旋逐渐向间隙外迁移且呈现出明显的周期性变化特征。涡量分析得到时均场的涡量大小与分布情况,通过与POD分析中瞬态场的含能大尺度结构分布相结合,揭示间隙外涡旋能量的来源与变化规律。通过前4阶瞬态脉动速度场重构,可以从微观时间尺度进一步说明瞬态速度场的突变性与周期性。研究成果将有助于加深对冲击射流本质的理解。 相似文献
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《流体机械》2016,(2):66-70
基于场协同强化理论,结合射流冲击的换热特点对常规毛细节流制冷系统进行优化,设计出一种新型的换热器装置。该换热器装置是将开孔毛细管内置到蒸发管中,使得制冷剂在节流后直接从毛细管沿轴向的不同孔口处冲击到蒸发管的内壁上蒸发换热,该冲击过程中由于速度场与温度梯度方向的协同性最大而具有显著的强化换热效果。首先,理论分析了毛细管进口速度(2m/s和0.5m/s)和开孔直径(1mm和0.5mm)的速度场与温度梯度方向的协同性,其次,在0MPa的回气压力下对该新型换热器装置进行性能试验,并以常规毛细节流系统作对比试验。试验结果表明,开孔试验中蒸发管表面的温度场比较稳定,而常规毛细试验中各测点由于毛细管节流的流量调节能力差而存在较大的波动。在蒸发压力和换热面积相同条件下,毛细试验的排气压力要比开孔试验高出13.6%,所以开孔试验的性能系数、制冷剂充注量比毛细试验更优;同时,毛细试验的压缩机功耗要比开孔试验高出9.1%,可见开孔试验系统的制冷效率比常规毛细试验的更高。开孔试验因为在多处射流冲击供液,并且射流冲击在冲击区中射流工质的流场和温度梯度场具有极好的协同度而能显著强化换热,使得蒸发管表面形成的温度场相对更均匀。 相似文献
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Sung Kook Hong Dong Hyun Lee Hyung Hee Cho 《Journal of Mechanical Science and Technology》2008,22(10):1952-1958
The objective of this paper is to investigate the heat/mass transfer characteristics on a concave surface for rotating impinging
jets. The jet with Reynolds number of 5,000 is applied to the concave surface and the flat surface, respectively. The rotating
experiments have been carried out at the rotating speed of 560RPM which is corresponding to Ro number of 0.075. The two jet
orientation (front and trailing orientation) are considered. Detailed heat/mass transfer coefficients on the target plate
were measured using a naphthalene sublimation method. The result indicates that the rotation leads to change in local heat/mass
transfer distributions and the slight increase in the Sh level. The front orientation induces asymmetric Sh distributions,
whereas the trailing orientation shows the shifted heat/mass transfer feature due to rotation-induced flow behavior. The crossflow
effect on heat/mass transfer is also observed as the streamwise direction increases. Compared to flat surface, the heat/mass
transfer on the concave surface is enhanced with increasing the spanwise direction due to the curvature effect, providing
the higher averaged Sh value. It is proved that the difference of surface geometry affects somewhat the local and averaged
heat/mass transfer regardless of rotation condition.
This paper was presented at the 9th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007. 相似文献
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Soon Hyun Yoon Moon Kyung Kim Dae Hee Lee 《Journal of Mechanical Science and Technology》1997,11(4):476-483
Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally
investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity
and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width)
ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward
the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of
the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger
than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity
caused by more active mixing of the jet flow. 相似文献