Qian Jian
Qian Jian, Professor of Physics at the University of Chinese Academy of Sciences, died in Beijing on 30 November 2018 after a cerebral hemorrhage.
Qian was born on 20 November 1939 in Wuxi City, Jiangsu Province, China. Qian graduated with the BSc degree from Peking University in 1963. From 1963 to 1965, Qian worked on high-temperature gas transport at the Institute of Mechanics of the Chinese Academy of Sciences in Beijing. From 1970 to 1988, Qian was affiliated with the Beijing Institute of Environmental Features. In 1979, when China had just opened its doors to the Western world, Qian went on to the Department of Mechanical Engineering at the City University of New York and did his PhD research under the supervision of Chan-Mou Tchen. Qian received his PhD in 1984. His PhD thesis is entitled “Closure Problems and Numerical Studies of Turbulence.” Qian was relocated to the Department of Physics Graduate School at the Chinese Academies of Sciences in Beijing in 1988. Qian was promoted to Full Professor in 1989; he retired in 2005.
Qian’s mind was mathematical. His mathematical talent was best illustrated by his first paper in Chinese, entitled “On the integral equations in the theory of mixed gas transport,” in Acta Physica Sinica in 1964. Although Qian received his academic training in the US, he did not bring the style of multiple-authored papers into mainland China, adhering instead to single-authorship papers, which is more typical of older-generation turbulence researchers like Geoffrey Ingram Taylor and Lewis Fry Richardson. Qian worked independently and published 27 single-authored international peer-reviewed papers dealing with aspects of the scaling properties of homogeneous, isotropic turbulence beginning in 1983. From 1983 to 1990, Qian published 11 papers on turbulence in Physics of Fluids and one in the Journal of Fluid Mechanics. From 1994 to 2002, Qian published six papers on turbulence in Physical Review E and one paper in Physical Review Letters. A Chinese research student was actually shocked by this level of productivity, since it was not easy, especially in the 1980s, for a Chinese physicist to have such a high publication rate in the top international fluid mechanics journals.
The theory of Homogeneous, Isotropic Turbulence (HIT), which was conceptually proposed by Lord Kelvin and developed mainly by Taylor and George Keith Batchelor, remains the major approach to the theoretical study of turbulence. HIT means a sure sign of success, as W. David McComb wrote in his book Homogeneous, Isotropic Turbulence. Qian made fundamental contributions to the numerical study of isotropic turbulence, profoundly establishing the Liouville’s equation–based isotropic turbulence theory using nonequilibrium statistical mechanics and a perturbation variation approach, which is compatible with the Kolmogorov spectrum. In his paper published in Journal of Fluid Mechanics in 1990, Qian applies his theory to further confirm Batchelor’s k-1 spectrum.
After Batchelor disseminated the theory of Andrey Nikolaevich Kolmogorov to the Western turbulence community in 1947, a number of researchers have sought to improve on the Kolmogorov [K41] analysis by matching solutions valid in the inertial subrange to those valid in the viscous dissipation range, i.e. considering finite Reynolds number effects on K41. Among them was Qian. An overview of “Qian’s method” appears in McComb’s book, which devotes three pages to Qian’s work, published in Physical Review Letters in 2000, on high-order structure functions of turbulence. Notably, Qian investigates whether the second-order exponent corresponds to normal Kolmogorov scaling or anomalous scaling. Qian’s method makes use of exact relationships incorporated with well-established data correlations available in the literature, so as to extract as much physics as possible from the experimental results.
In January 2000, Qian sent an email, part of which is reproduced below, to Robert (Bob) Antonia, who is Emeritus Professor at the University of Newcastle, Australia:
“Most scholars believe in the anomalous scaling of turbulence due to intermittency. In contrast to this prevailing point of view, we argue that the available data actually favors the K41 normal scaling rather than the anomalous scaling predicted by various intermittency models, if the data are properly interpreted by taking into account the finite Reynolds number effect which decays slowly. This result will change our understanding of turbulence. Enclosed please find my recent papers on this topic. It is interesting to make further experiments to prove or disprove the results of my papers.”
This email triggered subsequent exchanges of emails between Antonia and Qian during 2000 and 2001. In particular, it led to the realization (R. A. Antonia and P. Burattini, Journal of Fluid Mechanics 550, 175, 2006 ) that Kolmogorov’s famous 4/5 law can only be validated at extremely large Reynolds numbers for decaying HIT. Bob Antonia’s more recent work, in collaboration with Shunlin Tang, Lyazid Djenidi, Luminita Danaila, and Yu Zhou (R. A. Antonia et al., Journal of Fluid Mechanics 781, 727, 2015 ; R. A. Antonia et al., Physics of Fluids 29, 020715, 2017 ; S. L. Tang et al., Journal of Fluid Mechanics 820, 341, 2017 ; S. L. Tang et al., Journal of Fluid Mechanics 847, 244, 2018 ), provides strong support for Qian’s prediction that both the skewness and flatness factor of the velocity derivative approach constant values at large Reynolds numbers, which is in accordance with K41, as well as with Qian’s contention that the anomalous scaling most likely represents a Reynolds number effect.
Qian’s two important papers in 1984 and 1999, which are entitled “Universal equilibrium range of turbulence” (Physics of Fluids) and “Slow decay of the finite Reynolds number effect of turbulence” (Physical Review E), are also highlighted in the book Homogeneous Turbulence Dynamics published by Pierre Sagaut and Claude Cambon in 2018. As shown in Table 4.7 in the book, Qian’s work on the kinetic energy spectrum is listed together with the work done by Werner Heisenberg, Subrahmanyan Chandrasekhar, Robert Kraichnan, Philip Saffman, Stephen Pope, and Charles Meneveau.
Qian did not have his own research students. However, he was a premier teacher or mentor of other professors’ research students and young turbulence scientists in mainland China.
Even the best scientists feel the need for recognition. However, Qian received little of the recognition that he deserved in mainland China. Like others, I anticipate the merits of Qian’s contribution to turbulence will come to be recognized by more and more people in mainland China and the Western world. Just as The Master Confucius said, “To remain unsoured even though one’s merits are unrecognized by others, is that not after all what is expected of a gentleman?” This is the spiritual power of a real Chinese scholar, which Qian epitomized admirably. To whom be glory for ever and ever [Galatians 1:5].
