PhD Position in Wind Tunnel Experiments of Multiscale Topography in Turbulent Boundary Layers
Catholic University of Leuven

This PhD position is supervised by Prof. Johan Meyers (KU Leuven) and Prof. Raúl Bayoán Cal (Portland State University). The position is embedded in the FWO project “Development of roughness models for multiscale topography in neutral and stable atmospheric boundary layers”, funded by the Flemish Science Foundation. The project is a collaboration between the research group of Prof. Meyers at the department of Mechanical Engineering of KU Leuven and the research group of Prof. Raúl Bayoán Cal at the department of Mechanical Engineering of Portland State University (OR, USA). The PhD position is formally hosted at the university of Leuven, but will include a two-year research visit at Portland State University. It is one of two research positions on this project, with a focus on experimental work at the wind tunnel of Portland State University, as well as on the development of theoretical models to describe the effect of multiscale roughness on the boundary layer. The other PhD position focuses on the development of multiscale roughness models based on direct numerical simulation and large-eddy simulations.


Rough boundary layers are prevalent in many engineering applications and nature. A prime example is the atmospheric boundary layer (ABL) that is governed by the complex interaction of the wind system with land and structures.  Scales in terrain topography range from hundreds of meters (mountains, hills, buildings) down to submillimeter level (rocks, sand, plants). Modern LIDAR equipment can map terrain details down to centimeter resolutions. However, given current computational resources, simulations (e.g., Large-Eddy Simulations – LES) of the ABL use cell sizes ranging from 10 to 100 meters. Thus, terrain geometry can only be partly represented in simulations. Although rough boundary layers in engineering applications are commonly modelled in LES, approaches typically rely on homogenously distributed roughness with scales that are much smaller than the boundary layer height and the LES grid cells, so that a simple stress model based on roughness height suffices. In atmospheric boundary layer simulations, these type of roughness models are superposed on large-scale terrain features that are resolved by the grid. In recent years, there has been a renewed interest in surface roughness, as large secondary motions are excited by roughness arrangements that have horizontal heterogeneities with dominant spanwise length scales of the order of the outer length scale of the flow. In this case, the effect of roughness on the flow penetrates into the outer layer, such that simple parametrizations based on roughness length do not suffice. In the case of the atmospheric boundary layer, the topography may also extend (in height) into the outer layer of the boundary layer, invalidating classical arguments based on scale separation between roughness sublayer and outer layer. Moreover, the representation of multiscale roughness with a continuous range of scales (partly resolved and partly not resolved) is still a major modelling challenge, limiting predictive capabilities of simulations in many application areas, such as, wind energy, pollutant dispersion, industrial safety, urban planning, to name a few.
Research: The research concentrates on the development of next generation multiscale roughness models for the neutral and atmospheric boundary layers. The development of such models and new physical insight is based on wind-tunnel experiments (in stable and neutral conditions) and direct numerical simulations (at moderate Reynolds number) of situations including wind veer; seen as complementary to each other.  The current PhD concentrates on the design, set-up and execution of wind-tunnel experiments at the wind tunnel facility of Portland state university. Based on this, the research also looks into extending the theory of Meyers, Ganapathisubramani & Cal (J. Fluid Mech. 862, 2019) to stable stratification regimes. Finally, collaborative work will be pursued between both PhD students in the validation of new roughness models in large-eddy simulations.


The candidate must hold a Master degree in one of the following or related fields: fluid mechanics, aerospace or mechanical engineering, experimental methods, experimental fluid mechanics. The candidate should have a solid background and/or interest in fluid mechanics, experimental work, design and manufacturing of experiments, and laboratory work. Proficiency in English is a requirement. The position adheres to the European policy of balanced ethnicity, age and gender. All genders are encouraged to apply.


Start as soon as possible, and preferably before January 1st, 2021. The PhD position lasts for the duration of four years, and is carried out at the University of Leuven and at Portland State University. While in Leuven, the candidate also takes up a limited amount (approx. 10% of the time) of teaching activities. The remuneration is generous and is in line with the standard KU Leuven rates. It consists of a net monthly salary of about 2000 Euro (in case of dependent children or spouse, the amount can be somewhat higher).


To apply, use the KU Leuven online application platform (applications by email are not considered) Please include:
a) an academic CV and a PDF of your diplomas and transcript of course work and grades
b) a statement of research interests and career goals, indicating why you are interested in this position
c) a sample of technical writing, e.g. a paper with you as main author, or your bachelor or master thesis
d) two recommendation letters
d) a list of at least two additional references (different from recommendation letters): names, phone numbers, and email addresses
e) some proof of proficiency in English (e.g. language test results from TOEFL, IELTS, CAE, or CPE)

Please send your application as soon as possible.
Decision: as soon as a suitable candidate applies.
Starting Date: immediate start is possible. Start preferably before January 1st, 2021.

You can apply for this job no later than November 03, 2020 via the
KU Leuven seeks to foster an environment where all talents can flourish, regardless of gender, age, cultural background, nationality or impairments. If you have any questions relating to accessibility or support, please contact us at
  • Employment percentage: Voltijds
  • Location: Leuven
  • Apply before: November 3, 2020
  • Tags: Werktuigkunde

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