共查询到18条相似文献,搜索用时 187 毫秒
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纳米流以射流冲击方式对柴油机缸盖的冷却研究 总被引:1,自引:1,他引:1
利用纳米流射流冲击技术提升柴油机缸盖中进排气门鼻梁处的高热密度区域的传热系数,通过搭建研发的试验操作平台,对比了以不同体积分数的Cu-水纳米流作为冷却工质时,用射流技术对柴油机缸盖高热密度区域的传热效果。分析了射流冲击速率、射流冲击高度、射流冲击角度、纳米流体积分数及射流初始温度对缸盖高热密度区域传热系数的影响。研究结果表明:采用纳米流射流技术可实现良好的柴油机高热密度区域的传热效果,但不同的射流参数及纳米流体积分数会对传热效果产生不同的影响。 相似文献
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《可再生能源》2016,(2)
以应用在水平轴风力机叶片上的层流翼型S809为研究对象,采用CFD数值模拟技术,结合ShearStress Transport(SST)湍流模型,数值计算了S809翼型的升阻力特性。在翼型设计中应用一种转捩延迟控制技术——射流技术,即在翼型上翼面添加射流口,并研究了射流口位置和射流速度对翼型S809气动特性的影响。结果表明:射流技术能够显著提高翼型升力,延缓翼型失速;在低攻角下,射流速度大于来流风速才能提升翼型升力;在失速前,翼型的升力系数和失速攻角随着射流速度的增大而增大,在原始翼型失速而带射流翼型未失速阶段,带射流翼型的阻力系数明显小于原始翼型;射流速度一定时,射流口位置适当靠前可增大翼型的失速攻角,射流口位置布置在翼型上翼面中后部能使翼型在失速前获得较大的升力系数。 相似文献
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水舌挑距是泄洪消能最基本参数之一,消能形态、冲击区域、冲坑深度、水流衔接均与其密切相关。为研究高海拔地区气压降低对挑射流特性的影响,采用减压模型试验的方法研究了环境气压对水舌挑距的影响程度。结果表明,气压与水舌挑距呈良好的线性关系,气压越低,因空气阻力越小,水舌挑距越远;气压每下降15kPa,对水舌内缘与外缘的最大影响程度分别为1.67%、1.48%;低气压环境下水舌空中扩散与掺气减弱,水舌厚度变薄,水流呈集中趋势。基于气压与空气阻力影响系数关系,修正规范水舌挑距计算公式,为高海拔地区挑射流设计提供参考。 相似文献
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阵列射流冲击冷却流场与温度场的数值模拟 总被引:3,自引:0,他引:3
采用数值模拟方法对冲击冷却的流动和传热过程进行了三维数值研究。特别研究了在冲击孔叉排方式下,相邻孔间距、冲击距离以及射流入口雷诺数对冲击表面冷却流动传热特性的影响规律。 相似文献
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The role of jet inlet geometry in impinging jet heat transfer,modeling and experiments 总被引:1,自引:0,他引:1
Effects of jet inlet geometry and aspect ratio on local and average heat transfer characteristics of totally nine confined impinging jets have been investigated experimentally using thermochromic liquid crystals and numerically by using a 3-D low Reynolds number k–? model. Experimental study by using liquid crystals for temperature measurement was conducted for three different jet exit geometries (circular, elliptic, rectangular). In addition, simulations were performed at the same mass flow rate for totally nine jet exit geometries including circular, elliptic and rectangular jets with different aspect ratios for dimensionless jet to plate distances 2, 6, and 12.As the aspect ratio of equal cross-sectional area elliptic and rectangular jets increases, heat transfer enhancement in the stagnation region was obtained. As a result higher aspect ratio jets can be used as a passive enhancement technique for localized heating or cooling especially at small jet to plate distances. Wall jet region comprises very large portion of the impinging plate under study and generally lower heat transfer rates were attained for higher aspect ratio jets in this region especially at small jet to plate distances. Therefore as the aspect ratio increases, lower average heat transfer rates were acquired. The effect of aspect ratio on local and average heat transfer decreases with increasing jet to plate distance. Even though the mass flow rate is the same, heat transfer rate of rectangular jets were reduced with increasing the cross-sectional area. With increasing jet to plate distance very similar heat transfer characteristics were observed along the major and minor axis directions. 相似文献
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The flow field of confined circular and elliptic jets was studied experimentally with a Laser Doppler Anemometry (LDA) system. In addition, heat transfer characteristics were numerically investigated. Experiments were conducted with a circular jet and an elliptic jet of aspect ratio four, jet to target spacings of 2 and 6 jet diameters, and Reynolds number 10 000. The toroidal recirculation pattern was observed in the outflow region for both geometries at dimensionless jet to plate distance 2. Higher spreading rates in the minor axis direction of the elliptic jet have also been mapped. Along the target plate, different boundary layer profiles were obtained for circular and elliptic jets at H/d=2, but profiles became similar when dimensionless jet to plate distance was increased to 6. Positions of maximum radial and axial velocities and turbulence intensities have been determined for both geometries. For the confined circular and elliptic jet geometries, analysis of flow field measurements and numerical heat transfer results showed that inner peaks in local heat transfer closely relate to turbulence intensities in the jet and radial flow acceleration along the wall. Differences between the circular and elliptic jet, in terms of flow field and heat transfer characteristics, reduced with increase in the jet to plate distance. 相似文献
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阵列射流冲击冷却换热系数的数值研究 总被引:2,自引:0,他引:2
采用数值模拟方法对冲击冷却的流动和传热过程进行了三维数值研究.特别研究了在冲击孔叉排方式下,相邻孔间距、冲击距离以及射流入口雷诺数对冲击表面冷却流动传热特性的影响规律. 相似文献
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提出一个柴油喷雾与壁面碰撞的数学模型,可以计算垂直碰壁和倾斜碰壁时壁面射流的性能,适合于在准维燃烧模型中使用。建立了新的壁面射流贯穿距离计算公式,直观地反映了影响壁面射流传播的主要因素。与试验数据对比证实了这个模型的精度是令人满意的。在参数研究中,预测了喷孔直径、从喷孔至壁面的距离和喷射压力对壁面射流贯穿距离和区域空燃比的影响。 相似文献