I am a PhD student in the Department of Physics

at the University of Illinois at Urbana-Champaign.

I work with Professor Nigel Goldenfeld.

I am interested in critical phenomenon, non-equilibrium phase transition and turbulence.

Education

University of Illinois at Urbana Champaign (UIUC)Doctor of Philosophy in PhysicsResearch advisor: Professor Nigel Goldenfeld | Aug 2017 - present |

Tongji UniversityBachelor of Science in Applied PhysicsGraduated with "Outstanding Graduates" award | Sep 2013 - Jun 2017 |

Skills

Programming: | C, C++, Python, MATLAB, Mathematica, Julia |

Software & Tools: | LaTeX, Linux/Unix |

Language: | Chinese (native) , English (fluent) |

Awards

John Bardeen Award for outstanding graduate research in condensed matter physics at UIUC |

Outstanding Bachelor Thesis Research Award of Tongji University |

Shanghai Outstanding Graduates Award |

China National Scholarship |

Employee experience

Research assistant | Jun 2019 - present |

Teaching assistant of physics department at UIUC | Aug 2017 - May 2019 |

Summer research internship at University of British Columbia | Jul 2016 - Sep 2016 |

Teaching assistant of physics laboratory at Tongji University | Oct 2013 - Jul 2014 |

## Research

Generally speaking, I am interested in solving foundamental problems in physics using the tool of statistical mechanics.

I am particularly interested in critical phenomenon, non-equilibrium phase transition and turbulence, because the idea of universality these problems imply reveals the subtly and beauty in physics laws of nature.

Transition to turbulence

I am currently working on transition to turbulence from the perspective of non-equilibrium phase transition. Viewing the dynamics near the critical point as a result of the interaction and competition for energy between different modes, I model and analyze various behaviors of turbulent structures.

Generally, fluid becomes turbulent at a high Reynolds number. There are two routes to turbulence. One is through a supercritical bifurcation where the complexity of the flow gradually increases with increasing Reynolds number. The other is through a subcritical bifurcation, where non-laminar exhibits a high level of complexity upon its first appearance. I am interested in the latter that shows up in shear flow systems for instance.

The subcritical transition to turbulence is believed, following Pomeau's pioneering idea and later proved by experimental and DNS results, to be a non-equilibrium phase transition that belongs to the universality class of Directed Percolation.

I extended the model proposed by my collaborators and introduced mean flow-turbulence interaction to the model.

This resulting model gives the correct phenomenology of the turbulent puff, turbulent weak slug, turbulent strong slug in pipe flow. From this model, we can show that the puff-slug transition results from the competition between stochasticity and deterministic nonlinearity. This model can also be applied to other shear flow systems

Works on extending the simple model to more complicated two-dimensional shear flows and critical behavior are in progress.

Dynamics of large-scale circulation in turbulent rotating Rayleigh-Bénard convection

In my undergraduate years, I worked on large-scale circulation dynamics in turbulent rotating Rayleigh-Bénard convection. My collaborators built the Rayleigh-Bénard convection cell on a slowly rotating plane and operated it in the parameter regime where the large-scale circulation shows up. They measured how the average azimuthal rotating speed of the large-scale circulation plane changes with the Rossby number. In the large Rossby number region, they discovered an unexpected growth of the relative retrograde azimuthal rotating speed of circulation plane with increasing Rossby number. Existing theories could not explain this phenomenon.

From the experimental data, we found out that the growth of relative retrograde rotation speed is caused by rare stochastic events like cessation and reversal of the circulation plane that are neglected by existing theories. During these rare events, the circulation plane rotates much faster than usual.

To quantitatively check how much the rare events contribute to the abnormal growth, we started from the idea of an early model and a revised theory based on it, where the system is described by two Langevin equations with additive white noise that captures the dynamics of the azimuthal angular motion and the strength of the circulation plane.

By decoupling the linear rotating component, we were able to reduce the model to an Ornstein-Uhlenbeck process-like form and further estimate theoretical values of frequencies of rare events and average azimuthal displacement per event at different Rossby number region. Based on these values, we calculated theoretically how much the rare events contribute to total relative rotation speed, which agrees very well with experimental values. Thus, our conjecture was confirmed, and the abnormal increase of rotation speed was explained -- the behavior of the large-scale circulation during those stochastic rare events are indeed the major cause of the unexpected growth in retrograde relative plain rotation speed.

We also estimated correction to previous models from Reynolds stress by fitting the probability distribution functions of plane rotation speed and circulation strength.

I did part of the theory and most of the data analysis for this project.

## Publications

Xueying Wang, Hong-Yan Shih, Nigel Goldenfeld. Stochastic model for quasi-one-dimensional transitional turbulence with stream-wise shear interactions. (Under review by Phys. Rev. Lett., 2021).

Jin-Qiang Zhong, Hui-Min Li, Xue-Ying Wang. Enhanced azimuthal rotation of the large-scale flow through stochastic cessations in turbulent rotating convection with large Rossby numbers. Phys. Rev. Fluids 2, 044602(2017).

## Talks

Xueying Wang, Hong-Yan Shih, Nigel Goldenfeld. Emergence of puffs, weak and strong slugs from a stochastic predator-prey model for transitional turbulence with stream-wise shear interactions. APS DFD Meeting, 2020.

Xueying Wang, Hong-Yan Shih, Nigel Goldenfeld. Phase diagram of transitional pipe flow turbulence from a three trophic-level stochastic predator-prey model. APS March Meeting, 2021.