湍流热对流中的若干问题

对流是自然界中的一种常见现象,与人们的日常生产、生活息息相关。作为湍流和非线性系统的一个简单模型,在20世纪90年代以后,人们对热对流进行了系统而深入的研究。然而,直到现在,人们对湍流热对流的规律和本质仍然所知有限。文章主要从湍流传热、相干结构、大尺度环流和湍流中脉动量的小尺度统计等四个方面,简要地介绍了近年来湍流热对流的一些新进展。     

EXTENDED SELF SIMILARITY OF PASSIVE SCALAR IN RAYLEIGH-BNARD CONVECTION FLOW BASED ON WAVELET TRANSFORM

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Rayleigh-Bénard湍流热对流研究的进展、现状及展望

对流现象广泛存在于恒星和行星里.在地球上,对流现象在诸如大气、海洋、地核和地幔等众多动力学系统中起着重要作用.Rayleigh-Bénard(RB)湍流热对流系统是从这些复杂的自然现象中抽象出来的研究对流问题的经典流体力学模型.本文主要从湍流传热、羽流、大尺度流动结构、速度和温度脉动的小尺度统计和非传统RB对流等几个方面着重评述近年来RB对流的若干研究新进展,并对今后的研究做出展望.     

热湍流研究的新十年:从聚焦传统到延伸拓展

热湍流(浮力驱动湍流)作为一种典型的湍流现象,广泛存在于自然界和工程应用中. Rayleigh-Bénard (RB)湍流是从众多自然现象中抽象出来研究热湍流的经典模型, RB湍流的典型特征是系统中存在大尺度环流和羽流等不同尺度的湍流结构,这些结构通过作用于边界层,影响RB湍流的输运效率.因此,明确不同尺度湍流结构的生成、演化和作用机理,对理解RB湍流的输运特性至关重要,也是通过控制湍流结构调控输运效率的科学基础.本文重点从湍流结构的时空演化规律、输运特性、湍流调控和热湍流在其他领域的拓展四个方面评述近十年来RB湍流研究所取得的新进展,并对今后的研究方向做出展望.     

用子波方法研究Rayleigh-Bénard对流温度信号的标度律

采用子波分析方法 ,对实验中测得的Rayleigh_B啨ｎａｒｄ对流温度信号 (被动标量 )的标度律 ,从以下两个方面进行了研究 :第一方面 ,直接采用扩展的结构函数 (ESS)的公式对温度信号进行了分析 ,研究结果表明 ,采用该方法后的标度区域明显比不采用扩展结构函数的标度区域要宽 ,得到的标度指数与其它实验中得到的温度信号标度指数 ξ(q)一致 ;第二个方面 ,将 A .Arneodo等人对湍流中速度信号提出的基于子波分析的扩展标度公式 ,推广应用于温度信号 ,给出了一个描述温度信号的、基于子波分析的扩展标度公式 ,研究结果表明 ,提出的建立在子波系数极大模求和基础上的扩展标度公式 ,也能够比较准确地提取温度信号的标度指数 ξ(q) ·     

封面说明

封面图为利用热敏液晶技术在对流槽不同高度拍摄到的俯视图.图中颜色由红到绿再到蓝,代表了温度由低到高,通过选用较长的曝光时间(0.77s),拍摄到的图片可以记录下热敏液晶粒子的运动轨迹,由这些轨迹我们可以得到流场的分布.左图为距离对流槽上底板2mm处拍摄到的图片.图中粒子的     

EXTENDED SELF SIMILARITY OF PASSIVE SCALAR IN RAYLEIGH-BNARD CONVECTION FLOW BASED ON WAVELET TRANSFORM

Wavetet transform was used to analyze the scaling law of temperature data (passive scalar) in Rayleigh-Bénard convection flow from two aspects. The first one was to utilize the method of extended self similarity, presented first by Benzi et al., to study the scaling exponent of temperature data. The obtained results show that the inertial range is much wider than that one determined directly from the conventional structure function, and find the obtained scaling exponent agrees well with the one obtained from the temperature data in an experiment of wind tunnel. The second one was that, by extending the formula which was proposed by A. Arneodo et al. for extracting the scaling exponent ζ(q) of velocity data to temperature data, a newly defined formula which is also based on wavelet transform, and can determine the scaling exponent ξ(q) of temperature data was proposed. The obtained results demonstrate that by using the method which is named as WTMM (wavelet transform maximum modulus) ξ(q) correctly can be extracted.     

Rayleigh-Bénard湍流对流实验研究进展

近十年来,人们的注意力集中到关于Ｒｎｙｌｅｉｇｈ－Ｂｅｎａｒｄ硬湍流对流的研究,得到了硬湍流状态下温度场和速度场的主要特征,证实了大尺度环流在热对流中起主导作用等,但对大尺度环流与周围流体及热卷流的相互作用机理还不很清楚,硬湍流是否为Ｒｎｙｌｅｉｇｈ－Ｂｅｎａｒｄ对流的极限状态仍有不同看法,本文将对有关这方面的研究进展作一简要的回顾,并就今后的研究工作发表一些看法．     

Extended Self Similarity of Passive Scalar in Rayleigh-Bénard Convection Flow Based on Wavelet Transform

Wavetet transform was used to analyze the scaling law of temperature data utilize the method of extended self similarity, presented first by Benzi et al. , to study the scaling exponent of temperature data. The obtained results show that the inertial range is much wider than that one determined directly from the conventional structure function, and find the obtained scaling exponent agrees well with the one obtained from the temperature data in an experiment of wind tunnel. The second one was that, by extending the formula which was proposed by A. Arneodo et al. for extracting the scaling exponentζ(q) of velocity data to temperature data, a newly defined formula which is also based on wavelet transform, and can determine the scaling exponentζ(q) of temperature data was proposed.The obtained results demonstrate that by using the method which is named as WTMM ( wavelet transform maximum modulus )ζ(q) correctly can be extracted.