Heat Transport Characteristics of a Non-Premixed Turbulent Flame and nomaly in Heat Transfer : Counter-Gradient Diffusion

结果已在以下三篇论文中报道。摘要：(1)“估算燃烧流动中热电偶时间常数的双热电偶探针技术：一阶滞后系统的原位参数识别”：双热电偶探针由两个直径不等的细线热电偶组成，是一种估算热电偶时间常数的新技术，无需对热电偶响应进行动态校准。这种技术最适合测量湍流燃烧中的波动温度。在本研究中，对该技术的可靠性和适用性进行了评估，该技术适用于加热气缸（无燃烧）的湍流尾迹。同时使用快速响应的细丝电阻温度计（冷丝）提供参考温度。通过对冷丝测量和补偿热电偶测量结果的定量和详细比较，可以看出，除非热电偶信号中的噪声可以忽略不计和/或双热电偶探头的空间分辨率足够高，否则以前的估计方案会使它们的电偶时间常数小于适当值。对该方案进行了改进，使两个补偿热电偶输出之间的相关系数最大化。改进后的方案能更好地补偿热电偶响应。该方法一般适用于一阶滞后系统的原位参数辨识。(2)“高温湍流中速度和温度的同时测量”：本文讨论了一种简单可靠的同时测量包括燃烧在内的高温湍流中速度和温度的技术。该技术是基于激光多普勒测速仪（LDV）和补偿细线热电偶的组合。本研究的一个中心问题是发现所提出的技术的适用性和可靠性。为此，将带有细冷丝的双热电偶探头（Tagawa， Shimoji和Ohta， 1998）与LDV相结合，可以现场测量热电偶时间常数并精确补偿热电偶响应。该技术在加热圆柱后的湍流尾迹中进行了测试，其热场为常温且波动幅度较小。这使得测量精度的关键评估。结果表明，该方法具有较高的可靠性，可以有效地研究各种非等温湍流中的传热过程。(3)“弯曲矩形风道内湍流火焰的传热特性”：实验研究了弯曲矩形风道（180度弯曲）内非预混湍流火焰的传热特性。使用LDV和细线热电偶技术测量了速度和热场的关键湍流量，如雷诺应力分量和湍流热流。这些测量结果显示了反梯度热输运的直接证据，这可以归因于在弯曲管道径向上存在强压力梯度。温度场的阴影成像技术揭示了流动高压侧和低压侧燃烧气体包的完全不同的行为，这有助于解释燃烧湍流中反梯度热输运的发生机制。少

The results have been reported in the following three papers. The abstracts are :(1) "A two-thermocouple probe technique for estimating thermocouple time constants in flows with combustion : in situ parameter-identification of a first-order lag system" : A two-thermocouple probe, composed of two fine-wire thermocouples of unequal diameters, is a novel technique for estimating thermocouple time constants without any dynamic calibration of the thermocouple response. This technique is most suitable for measuring fluctuating temperatures in turbulent combustion. In the present study, the reliability and applicability of this technique are appraised in a turbulent wake of a heated cylinder (without combustion). A fine-wire resistance thermometer (cold wire) of fast response is simultaneously used to provide a reference temperature. A quantitative and detailed comparison between the cold-wire measurement and the compensated thermocouple ones shows that a previous estimation scheme gives ther … More mocouple time constants smaller than appropriate values, unless the noise in the thermocouple signals is negligible and/or the spatial resolution of the two-thermocouple probe is sufficiently high. The scheme has been improved so as to maximize the correlation coefficient between the two compensated- thermocouple outputs. The improved scheme offers better compensation of the thermocouple response. The present approach is generally applicable to in situ parameter-identification of a first-order lag system.(2) "Simultaneous Measurement of Velocity and Temperature in High Temperature Turbulent Flows" : This paper deals with a simple and reliable technique for simultaneous measurement of velocity and temperature in high-temperature turbulent flows, including combustion. The technique is based on the combination of a laser Doppler velocimeter (LDV) and a compensated fine-wire thermocouple. A central issue of this study is to find the applicability and reliability of the technique proposed. For this purpose, a two-thermocouple probe with a fine cold wire (Tagawa, Shimoji and Ohta, 1998), which enables in situ measurement of thermocouple time constants and accurate compensation of the thermocouple response, is combined with the LDV.The technique is tested in a turbulent wake behind a heated cylinder, whose thermal field is of ordinary temperature and fluctuates with relatively small amplitude. This enables critical assessment of the measurement accuracy. The results show that the technique is highly reliable and is effective in investigating heat transport processes in various non-isothermal turbulent flows.(3) "Heat transport characteristics of a turbulent flame formed in a curved rectangular duct" : Heat transport characteristics of a non-premixed turbulent flame formed in a curved rectangular duct (180-degree bend) are investigated experimentally. Key turbulence quantities of velocity and thermal fields such as Reynolds stress components and turbulent heat fluxes are measured using a combined LDV and fine-wire thermocouple technique. These measurements show direct evidence of the occurrence of counter-gradient heat transport, which can be ascribed to the existence of a strong pressure gradient in the radial direction of the curved duct. The shadowgraph technique for visualizing the temperature field reveals totally different behavior of the burned gas parcels between the high- and the low-pressure sides of the flow, and the observations may help us explain the mechanism of the occurrence of the counter-gradient heat transport in turbulent flows with combustion. Less