Imperial College London

Dr John Craske

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Lecturer in Fluid Mechanics
 
 
 
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Contact

 

+44 (0)20 7594 9702john.craske07 Website

 
 
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Assistant

 

Miss Rebecca Naessens +44 (0)20 7594 5990

 
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Location

 

328BSkempton BuildingSouth Kensington Campus

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Summary

 

Summary

My research involves the modelling and optimisation of flow physics for the built environment. Part of this work comprises fundamental studies of mixing in buoyancy-driven turbulence. Another part concerns the representation of open and closed systems using bulk models and network thermodynamics for the prediction and control of temperature and ventilation in buildings. In this regard, I am particularly interested in questions relating to system robustness, the composition and interaction of systems, data assimilation and optimal control.

My background is in fluid mechanics (at Imperial College London) and architecture (at the Bartlett, UCL). I am an associate member of the Institute of Mathematics and its Applications and a member of their London Branch committee.


Here is a summary of recent and current projects:


This figure shows the phase-space trajectory of an emptying filling box that is subjected to the `smallest' variation in an opposing wind that is sufficient to permanently reverse the flow. The vertical axis corresponds to the height of a density interface and the horizontal axis corresponds to the buoyancy (temperature) of the upper layer.

The robustness of natural ventilation

Buildings that are naturally ventilated admit multiple steady states and changes in their external environment can produce transitions between such states. Graham Hughes and I have looked in detail at the `stability' properties of a single room, heated by an isolated point source, that is subjected to changes in an opposing wind. The animation below shows the system's phase space in terms of the height of a density interface and upper layer buoyancy. The inset figure shows the profile of the `smallest' change in the wind that is sufficient to permanently reverse the original forward displacement ventilation. For further details see JFM 199.


The energetics of confined turbulent plumes

With Megan Davies Wykes (University of Cambridge) I have been looking in detail at flow driven by isolated sources of heat in confined spaces (see arXiv). Here's an image from a direct numerical simulation that shows how much energy the flow expends in mixing regions of different density:

BPE production by confined turbulent plumes

The video below combines the information above (blue) with the viscous dissipation of kinetic energy (red) to illustrate differences in their spatial distribution.

The instantaneous dissipation of kinetic energy (red) and (available) potential energy (blue) above an isolated source of heat in a confined and stratified environment from a direct numerical simulation (see https://arxiv.org/abs/1808.04625).

The statistical topology of enstrophy

With Jean-Paul Mollicone and Maarten van Reeuwijk, I have been looking into the statistical topology of enstrophy in temporal jets. This involves quantifying how isosurfaces of enstrophy are connected in space in an effort to discriminate different turbulent flows. Here's a picture showing isosurfaces corresponding to extrema of the Euler characteristic (e.g. maximising the number of `voids' in the enstropy field):


Enstrophy




Publications

Journals

Craske J, Davies Wykes M, The entrainment and energetics of turbulent plumes in a confined space, Journal of Fluid Mechanics, ISSN:0022-1120

Craske J, Hughes G, 2019, On the robustness of emptying filling boxes to sudden changes in the wind, Journal of Fluid Mechanics, Vol:868, ISSN:0022-1120

Craske J, 2019, Adjoint sensitivity analysis of chaotic systems using cumulant truncation, Chaos, Solitons and Fractals, Vol:119, ISSN:0960-0779, Pages:243-254

Craske J, Salizzoni P, van Reeuwijk M, 2017, The turbulent Prandtl number in a pure plume is 3/5, Journal of Fluid Mechanics, Vol:822, ISSN:1469-7645, Pages:774-790

Van Reeuwijk M, sallizoni P, Hunt GR, et al., 2016, Turbulent transport and entrainment in jets and plumes: A DNS study, Physical Review Fluids, Vol:1, ISSN:2469-990X

More Publications