Henri Bénard

Henri Claude Bénard (25 October 1874 – 29 March 1939) was a French physicist, best known for his research on convection in liquids that now carries his name, Bénard convection. In addition, the historical surveys of both TokatyG. A. Tokaty, 1994: A History and Philosophy of Fluid Mechanics (Dover, pp 168–169). and von KármánT. von Kármán, 1954: Aerodynamics: Selected Topics in the Light of Their Historical Development (Cornell University Press, Ithaca), pp. 68–69. both acknowledge that Bénard studied the vortex shedding phenomenon later named the Kármán vortex street, prior to von Karman's own contributions. Bénard specialized in experimental fluid dynamics, and the use of optical methods to study it. He was a faculty member at the universities at Lyon, Bordeaux, and finally the Sorbonne in Paris.See Wesfried (2006).

Bénard defended his PhD thesis at the Collège de France on 15 March 1901 entitled "".

Bénard was elected President of the French Society of Physics (SFP) in 1929, following the presidency of Louis Lumière. vols. 255–271. He was succeeded as President the next year by his friend and former teacher, Jean Perrin. In 1929 Bénard received the Bordin Prize for his work on vortices from the French Academy of Sciences., vol. 189, p. 1161 (1929). After his death in 1939, his widow received the Poncelet Prize on his behalf, also from the French Academy of Sciences., vol. 209, p. 918 (1939).

A research center of the ERCOFTAC in Lyon is named after him.http://www.lmfa.ec-lyon.fr/Henri.Benard

Life and career

Early and student years Henri Bénard was the only son of a small investor, Felix A. Bénard (1851–1884), and his wife Hélène M. Mangeant (1837–1901).Wesfreid (2006, p. 9); C. Charle and E. Telkes (1989). Les Professeurs de la Faculté des Sciences de Paris: Dictionnaire Biographique 1901–1939 (INEP Éditions du CNRS), pp. 33–34. He attended elementary school in Lisieux and Caen and high school at the Lycée Louis-le-Grand. In 1894, Bénard was one of 17 students selected from 307 candidates to attend the École normale supérieure (ENS) in the sciences section. His classmates there included Henri Lebesgue and Paul Langevin,Wesfried (2006). and one of his teachers was Jean Perrin.Bull. Soc. Franc. Phys., vol. 271, pp. 5S–6S. Bénard received his teaching degree in physics in 1897, and then began working as an assistant to Éleuthère Mascart and Marcel Brillouin at the Collège de France in Paris. At this time, Bénard joined the French Society of Physics (SFP).Chevenard (1939).

Bénard's initial scientific efforts related to the optical rotation of sugars, resulting in papers co-authored with MascartE. Mascart and H. Bénard (1899). Sur le pouvoir rotatoire du sucre. Ann. Chim. Phys., series 7, vol. 17, pp. 125–144. and ENS chemistry student L.-J. Simon.L.-J. Simon and H. Bénard (1901). Sur les phénylhydrazones du d glucose et leur multirotation. Compt. Rend. Acad. Sci. vol. 132, pp. 564–566. The first of these was an experimental measurement of the angle of rotation of polarized light by pure sugar in solution, to determine its concentration for use in saccharimetry, undertaken at the request of the Commission on Sugars and Alcohols, of the Ministry of Finances. Bénard's results were adopted as the legal values in France by the Ministry of Finances.H. Bénard (1926). Notice sur les Titres et Travaux Scientifiques de M. Henri Bénard (Gauthier-Villars, Paris), Sec. 1. Meanwhile, Marcel Brillouin was teaching a course on the viscosity of liquids and gases, and asked Bénard to repeat Poiseuille's experiments on water flow rates in capillary tubes.H. Bénard (1926). Notice sur les Titres et Travaux Scientifiques de M. Henri Bénard (Gauthier-Villars, Paris), Sec. 2. However, Brillouin also wanted experiments done with mercury instead of water. Bénard's results (undertaken in the first 6 months of 1899) were summarized in 1907 in Brillouin's textbook based on the course.M. Brillouin (1907). Leçons sur la Viscosité des Liquides et des Gaz (Gauthier-Villars, Paris), vol. 1, pp. 152–154. Brillouin also supervised the translation into French of Boltzmann's textbook on kinetic theory of gases, by Bénard and Alexandre Gallotti.L. Boltzmann (1905). Leçons sur la Théorie des Gaz (Vol. 2, Gauthier-Villars, Paris), translated by A. Gallotti and H. Bénard, with an introduction and notes by M. Brillouin.

The subject of Bénard's dissertation was cellular thermal convection, inspired by accidental observations made by Adrien Guebhard of convection in a bath of abandoned film developer. Working in Mascart's lab, Bénard carried out the first controlled, systematic scientific experiments on convection in a shallow layer of fluid heated from below.E.L. Koschmieder, 1993: Bénard Cells and Taylor Vortices (Cambridge University Press). He found that the convective motions organized themselves in semi-regular, semi-permanent cellular patterns. Upflows occurred in the centers of the cells and downflows occurred at their peripheries. There was also a slight depression of the upper free surface of the fluid at each cell center, leading Bénard to speculate about the role of surface tension. He also measured the aspect ratio of the cells and discovered that there was a critical temperature below which no convection occurs. Unfortunately, he attributed this to the solidification of the fluid he was using (spermaceti, a whale oil that is solid at room temperature). Ironically, Bénard would much later become a skeptic about the very concept of the critical temperature difference, although he discovered it.E. L. Koschmieder, 1993: Bénard Cells and Taylor Vortices (Cambridge University Press).H. Bénard, 1931: Discussion of A. R. Low, Multiple modes of instability of a layer of viscous fluid, heated from below, with an application to meteorology. In Proceedings of the Third International Congress for Applied Mechanics (1930), Vol. 1. Stockholm: Ab. Sveriges Litografiska Tryckerier, p. 120. In 1900–1901, Bénard presented the results of this work (and the associated optical methods) in four different journals, the Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences,H. Bénard, 1900. Compt. Rend., vol. 130, pp. 1004–1007, 1065–1068. the Revue Générale des Sciences Pures et Appliquées et Bulletin de l'Association Française pour l'Avancement des Sciences,H. Bénard, 1900. Rev. Gén. Sci. Pures Appl. vol. 11, pp. 1261–1271, 1309–1328. the Journal de Physique Théorique et Appliquée,H. Bénard, 1900. J. Phys., series 3, vol. 9, pp. 513–524; H. Bénard, 1901. J. Phys., series 3, vol. 10, pp. 254–266. and the Annales de Chimie et de Physique.H. Bénard, 1901. Ann. Chim. Phys., series 7, vol. 23, pp. 62–144. He also presented his findings to at least two scientific meetings,H. Bénard, 1900. Comptes-Rendus de l'Association Française pour l'Avancement des Sciences, Congrès de Paris (1900), pp. 446–467; H. Bénard, 1900. Séances de la Société Française de Physique, année 1900, pp. 202–213. as well as in the first thesis of his dissertation. (The second part of his thesis dealt with optical rotation in sugars.) This work laid the foundation for the study of Rayleigh–Bénard convection, the buoyancy-driven flow of fluid confined between horizontal conducting surfaces, with the higher temperature at the bottom; and Bénard–Marangoni convection, the surface-tension-driven flow of a fluid with an upper free surface and a heated, conducting surface at the bottom. These problems have continued to occupy scientists beginning with Lord Rayleigh and continuing into the 21st century.

Bénard spent two months as a high-school teacher in Cherbourg (Oct.-Nov. 1900) before acquiring a pension from the Thiers Foundation (Nov. 1900–April 1902). He defended his dissertation on 15 March 1901, at the age of 26, and was awarded the Docteur ès Sciences physiques, mention très honorable. His dissertation committee consisted of Gabriel Lippmann, Edmond Bouty, and Émile Duclaux. In September 1901, Bénard attended the conference of the British Association at Glasgow, where he observed a number of notable British physicists, such as Lord Kelvin, Silvanus P. Thompson, Andrew Gray, and Joseph Larmor.H. Bénard, 1900: Controverse sur la question des effets magnétiques de la convection électrique au congrès de l'Association Britannique, a Glasgow. J. Phys., series 3, vol. 10, pp. 517–519. Unfortunately, an "excess of modesty" (Bénard's own wordsBénard (1926), p. 30.) prevented him from showing the results of his work to Lord Kelvin in Glasgow, as well as at the earlier Paris conference.H. Bénard, 1900. Comptes-Rendus de l'Association Française pour l'Avancement des Sciences, Congrès de Paris (1900), pp. 446–467. Kelvin's late brother, James Thomson, had studied thermal convection qualitatively prior to Bénard's work.

On 23 December 1901 Bénard married Clémentine Olga Malhèvre, a few months after his mother's death; they had no children.Wesfried (2006), p. 13.

Lyon Bénard was appointed a senior lecturer at the university at Lyon (1902), in charge of introductory courses.Wesfried (2006), p. 13. Despite his teaching load, in 1904 he began experimental studies of vortex shedding behind an obstacle; the work was carried out in a cellar.Schereschewsky (1976). In 1906 he began using a cinema camera to record these phenomena. Initial publications of this work occurred in 1908,H. Bénard, 1908. Compt. Rend. vol. 147, pp. 839–842, 970–972. but the films would not be fully utilized until the 1920s. Nonetheless, Benard's experimental work in Lyon was the beginning of his contribution to the study of what we now call the Kármán vortex street.

Bordeaux In 1910, Bénard moved to Bordeaux, where he was now a professor and chair of general physics. One of his colleagues there was Pierre Duhem.Wesfreid (2006), p. 13. Bénard continued to study vortex shedding, analyzing the Lyon films to measure the wavelength and frequency of vortex shedding as other parameters are varied, such as the flow speed and the geometry of the obstacle. He also made films of thermal convection.

Also in 1910, Bénard began collaborating with Camille Dauzère (1869–1944), who became a key collaborator in Bénard's fluid dynamics research. Dauzère studied the problems of thermal convection and solidification, prompting Bénard himself to revisit the topicH. Bénard, 1911. Ann. Chim. Phys., series 8, vol. 24, pp. 563–566. and even speculate, based on Dauzère's work, that the lunar craters may have been formed by thermal convection and solidification.H. Bénard, 1913. Compt. Rend., vol. 156, pp. 882–884. Henri Deslandres had also noticed the analogy with lunar craters, as well as pointing out (correctly, as it turns out) a further analogy with solar granulation.H. Deslandres, 1912. Compt. Rend., vol. 154, pp. 976–977.

In 1913–1914, Bénard and Dauzère made a series of eight films, on convection and solidification in an evaporating fluid, which were produced with the aid of a large firm, Gaumont.H. Bénard and C. Dauzère, 1914: Notice sur une série de films obtenus dans les laboratoires Gaumont, juillet–octobre 1913. Société des Établissements Gaumont. Also in these years, the two scientists received subsidies from the Bonaparte Fund, administered by the French Academy of Science, for their research.Compt. Rend., vol. 157, pp. 250, 1311–1312 (1913); vol. 159, p. 941 (1914).

Dauzère completed his Ph.D. in 1919 in Paris, after spending a year doing solidification experiments under Charles Fabre in Toulouse.Wesfreid (2006), p. 19. Dauzère then became director of the Pic du Midi observatory in 1920 until his retirement in 1937.

In 1919, Bénard was elected to the Council of the University of Bordeaux,C. Charle and E. Telkes (1989). Les Professeurs de la Faculté des Sciences de Paris: Dictionnaire Biographique 1901–1939 (INEP Éditions du CNRS), pp. 33–34. and he began publishing the results of his wartime work (see next section).

World War I