Fluid dynamics research

My research focuses on buoyancy-driven mixing and the development of stratification in confined environments.

Institution: University of Bristol
Supervisors: Dr Andrew Lawrie and Dr Stuart Thomson
Discipline: Applied mathematics and fluid dynamics

Fluorescent dye showing a plume and mixing layers in a laboratory tank — A laboratory plume visualised using planar laser-induced fluorescence.

PhD research

My thesis is titled Mixing behaviour of plumes. I began the PhD in November 2022 and submitted my thesis in October 2026. I am awaiting my viva. My PhD research is funded by Nuclear Waste Services through its Research Support Office.

My PhD addresses an engineering problem arising in the safe storage of nuclear waste. Water radiolysis can generate hydrogen gas, creating a safety concern if combustible or explosive mixtures accumulate within a vault. Predicting this hazard requires understanding how a lighter fluid released into a denser ambient mixes, spreads and becomes density stratified over time.

I study this process experimentally using fresh water released into denser salt water. The system is dynamically analogous to hydrogen released into air, while being easier to control and measure in the laboratory. The evolving density field is obtained using planar laser-induced fluorescence.

Experimental measurements are used to develop and test mathematical models for the growth of stratified layers. I also use finite-element simulations in FEniCS to examine aspects of the plume dynamics that complement the experiments.

Methods: laboratory experiments, planar laser-induced fluorescence, conservation-based scaling models, reduced-order theory and finite-element simulation.

Current research topics

Buoyant plume dynamics in confined environments
Mixing and stratification following plume impingement
Laminar plumes with and without ventilating crossflow
The influence of enclosure geometry and source configuration
Reduced-order models for the evolution of density profiles
Validation of theory against laboratory measurements

Research software

PLIF acquisition system. C receiver and BeagleBone control code for continuous DALSA image acquisition and storage on request. GitHub · Archived software (Zenodo).
Stratified plume experimental analysis. MATLAB tools for greyscale stratification-depth measurements and fluorescence-based density reconstruction. GitHub · Archived software (Zenodo).
FEniCS stratification modelling. Legacy FEniCS solvers and post-processing for Cartesian, axisymmetric and three-dimensional plume models. GitHub · Archived software (Zenodo).

Research data

Plume simulation datasets (2026). Saved fields, profiles and mesh and time-step sensitivity comparisons from my PhD research: 2D Cartesian, 2D axisymmetric and 3D rectangular (Zenodo).
Experimental apparatus: CAD models and intake-design calculations; design archive (Zenodo, 2026).

MSc research project co-supervision

From January to September 2026, I co-supervised an MSc research project at Bristol investigating density-layer development from single and twin buoyant plumes, providing day-to-day research guidance. The project was titled Stratification Development in a Confined Region: An Experimental Comparison of Density-Layer Development Generated by Single- and Double-Nozzle Buoyant Flows.

Talks and presentations

On the mixing behaviour of plumes in a confined environment — Osborne Reynolds Day, June 2026.
On the mixing behaviour of plumes in a confined environment — British Applied Mathematics Colloquium (BAMC), Norwich, March 2026. View the programme (PDF).
How does hydrogen build up in a closed vault environment? — NWS RSO Annual Conference, Manchester, January 2026.
Mixing behaviour of plumes — 2nd European Fluid Dynamics Conference (EFDC2), Dublin, August 2025.
Hydrogen ventilation in a GDF — NWS RSO Annual Conference, Bristol, January 2025.
Mixing behaviour of laminar plumes with and without a ventilating crossflow — NWS RSO Annual Conference, Sheffield, January 2024. Read the conference report.
Ventilation of hydrogen in UILW vaults — NWS RSO Advanced Manufacturing Webinar (online), October 2023. Watch the recording.
Hydrogen ventilation in a geological disposal facility — NWS RSO Annual Conference, Leeds, January 2023.
The motion of anisotropic carbon nanoparticles in shear flow: a hydrodynamic perspective — Cambridge Mathematics Placements (CMP) Presentation Day, August 2022.

Undergraduate mathematics talk

In 2019, I gave a talk on sphere packing to my undergraduate cohort at Murray Edwards College, Cambridge.

Earlier research

Cambridge Mathematics Open Intern, Faculty of Mathematics (July–August 2022)

During an eight-week project supervised by Dr Catherine Kamal, I investigated the dynamics of a Navier-slip ellipsoid in shear flow as a model for anisotropic carbon nanoparticles. The project considered particle orientation and motion in viscous flow, and I presented the work at the Cambridge Mathematics Placements Presentation Day. View the Cambridge past-projects listing.

Work in preparation

Arij Asad, Andrew G. W. Lawrie and Stuart J. Thomson, On the mixing behaviour of plumes in a confined environment.
Arij Asad, Andrew G. W. Lawrie and Stuart J. Thomson, Stratification development in a laminar crossflow.
Arij Asad, Andrew G. W. Lawrie and Stuart J. Thomson, Stratification development in a confined circular domain with and without laminar crossflow.