This year’s recipient of the Overijssel PhD Award is Xiaojue Zhu. He receives the award from Eddy van Hijum, member of the Provincial Executive of Overijssel responsible for Economic Affairs, at Twente’s 57th Dies Natalis, the university’s traditional Foundation Day celebration.
Prof. Detlef Lohse and Prof. Roberto Verzicco supervised Zhu’s dissertation, with Zhu obtaining his doctorate, cum laude, in February 2018. His thesis is entitled “Taylor-Couette and Rayleigh-Bénard turbulence: the role of the boundaries”. Most people know turbulence mainly as an unpleasant phenomenon they experience while flying, but it also affects our everyday lives. The more we learn about turbulence, the better we are able to understand the weather, the climate and ocean currents. Turbulence also affects the flow of blood in our large blood vessels, which plays a role in heart-valve replacement surgery.
What makes Zhu's doctoral thesis so remarkable is the breakthrough it has brought about in a classic subject in the field of hydrodynamics: the scaling law for so-called ultimate turbulence. In 1962, Robert Kraichnan had hypothesized a scaling relation for this regime, but since it only applies to exceptionally strong turbulence its workings had never been studied in detail. In his dissertation, Zhu showed that he had been able to numerically achieve this ‘ultimate turbulent regime’ and compare the results with corresponding experiments in his Physics of Fluids group in Twente.
In particular, Zhu could enhance the turbulence with wall roughness – the boundaries mentioned in the title. Roughness elements differ from each other in terms of shape, size, density and position. An important question is whether different types of roughness have different effects on transport and flow structure. This may sound simple, but it is extremely complex.
Zhu combined his numerical simulations with physical experiments done in the Physics of Fluids group, with the numerical and experimental data complementing each other perfectly and providing explanations for turbulent flow and current behaviour at different degrees of wall roughness. In less than four years, Zhu not only changed the research landscape with regard to turbulence, but he also gained insights and achieved results that no one could have ever dreamed of.
During his PhD research, Xiaojue Zhu was part of the Physics of Fluids department at the Science and Technology faculty’s MESA+ Institute. He has already published 20 articles in leading professional journals. Zhu is currently a much sought-after keynote speaker at international conferences. He has won the ninth annual NWO Physics Thesis Prize, which he will receive in February 2019. Zhu recently accepted a postdoc position at Harvard University.
The Overijssel PhD Award spotlights PhD research of an exceptionally high academic quality that marks the beginning of a promising career in the scientific field. The award is sponsored by the Province of Overijssel and consists of a certificate and €5,000. Each of the University of Twente’s faculties and research institutes was allowed to nominate one doctoral thesis for the award.