分类： 动力与电气工程 >> 工程热物理学 提交时间： 2018-01-24 合作期刊: 《热科学学报》
摘要： To investigate the role of a single shield on steady temperature measurement using thermocouples in hot air flow, a methodology for solving convection, conduction, and radiation in one single model is provided. In order to compare with the experimental results, a cylindrical computational domain is established, which is the same size with the hot calibration wind-tunnel. In the computational domain, two kinds of thermocouples, the bare-bead and the single-shielded thermocouples, are simulated respectively. Surface temperature distribution and the temperature measurement bias of the two typical thermocouples are compared. The simulation results indicate that: 1) The existence of the shield reduces bead surface heat flux and changes the direction of wires inner heat conduction in a colder surrounding; 2) The existence of the shield reduces the temperature measurement bias both by improving bead surface temperature and by reducing surface temperature gradient; 3) The shield effectively reduces the effect of the ambient temperature on the temperature measurement bias; 4) The shield effectively reduces the influence of airflow velocity on the temperature measurement bias.
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-06-26 合作期刊: 《热科学学报》
摘要： This paper presents experimental measurements of the flow field in a Low-speed Turbine Cascade using a stereoscopic particle-image velocimetry (SPIV). During the measurements, a pair of frame-straddling-based CCD cameras were configured at different sides of the laser light sheet, and appropriate tracing particles (DEHS) were employed. The measurements were conducted at the incidence angle of 0 degree and exit Reynolds number of 1.7 x 10(5) with the tip clearance 1.18% of blade chord. The tip flow features, such as the evolution and breakdown of tip leakage vortex, the horseshoe vortex, turbulence characteristics of tip leakage flow, were studied for the flow field analysis. The results showed that the tip leakage flow/vortex mainly dominate flow fields in the tip region. The tip leakage vortex performs as a concentrated vortex before its breaking down and splitting into small vortices. The highest turbulence intensity mainly occurs in the tip region along with the trajectory of tip leakage vortex, and when the vortex breaks down, the turbulence intensity reduces rapidly. Additionally, the SPIV with this configuration also shows an advantage in investigating the flow structures and mechanism inside the turbine cascade.
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-06-22 合作期刊: 《热科学学报》
摘要： Pipes are widely used to transport gas, oil and water in industries. Drag reduction in pipes is an increasingly concerned problem to save energy. Some researches have indicated that the non-smooth surface with special structures can reduce flow loss. In this paper, an experimental investigation has been performed on the effects of a kind of surface groove on the drag in both rectangular and circular duct at different Reynolds numbers. In the experiment of the rectangular duct, total pressure at both inlet and outlet were measured. Static pressure on the wall was measured on the surface with smooth and grooved film respectively. In the circular duct, a boundary layer pressure probe was used to measure the total pressure distribution at both inlet and outlet. Four taps at inlet and outlet were used to measure static pressure. The loss coefficient is used to evaluate the effects of the surface groove on drag reduction. The experiment was conducted with the Reynolds number range from 1.28x10(4) to 2.57x10(4). The result shows a maximum drag loss reduction of approximately 2.4% in rectangular duct at Reynolds number of 2.4x10(4). A 10% reduction of pipe pressure loss by grooved surface is measured in circular duct at a Reynolds number of 3.0x10(5).
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