Merge branch 'pub/update_hackathon' into 'master'

Pub/update hackathon

See merge request !10

pubs-2020.bib

@@ -229,7 +229,71 @@
   author = {Cooke, Emma},
   year   = {2020},
   school = {Imperial College London},
-  groups = {thesis}
+  groups = {thesis},
+  doi = {10.25560/83744},
+  abstract = { Destabilisation effects of forward facing steps,
+                  backward facing steps and bumps on stationary and
+                  travelling crossflow disturbances are investigated
+                  computationally for a 40 degree infinitely swept
+                  wing. Step and bump heights range from 18\% to 82\% of
+                  the boundary layer thickness and are located at 3\%,
+                  10\% and 20\% chord. The spectral/hp element solver,
+                  Nektar++, is used to compute base flow profiles with
+                  an embedded swept wing geometry. Parabolised
+                  Stability Equations (PSE) and Linearised Harmonic
+                  Navier-Stokes (LHNS) models are used to evaluate
+                  growth of convecting instabilities. The presence of
+                  surface step features impose an extremely rapidly
+                  varying flow field locally, which requires accurate
+                  resolution of the perturbed flow field. Derivations
+                  of these PSE and LHNS models incorporating the
+                  excrescence (PSEh, LHNSh) are elucidated. Unlike the
+                  PSE, which suffer from a stream-wise numerical step
+                  size restriction, the LHNS are a fully elliptic set
+                  of equations which may use an arbitrarily fine grid
+                  resolution. Unsurprisingly, the PSE codes fail to
+                  capture the effect of abrupt changes in surface
+                  geometry introduced by the step features. Results
+                  for the LHNS and roughness incorporating LHNSh are
+                  given for the varying vertical step and ramped type
+                  steps. Comparisons are made between the LHNSh model
+                  and direct numerical simulations involving the
+                  time-stepping linearised Navier-Stokes solver
+                  (NekLNS) in the Nektar++ software framework. Most
+                  previous work in the topic area has focused on
+                  Tollmien-Schlichting perturbations over
+                  two-dimensional flat plate flows or aerofoils, the
+                  novelty of this work lies with analysing crossflow
+                  instability over a swept wing boundary-layer flow
+                  with step features. PSEh and LHNSh models are tested
+                  with convecting Tollmien Schlichting instability
+                  over a dimple and randomly distributed roughness on
+                  an overall flat plate flow. The dimple case performs
+                  very well whereas it is more difficult to obtain
+                  converged results with the random roughness case,
+                  likely due to large stream-wise velocity gradient
+                  changes. A 45degree ramped shape roughness is
+                  investigated and remarkably good agreement between
+                  the LHNSh solution and NekLNS solution is
+                  found. Forward facing ramps and steps are found to
+                  act as greater amplifiers with increased height,
+                  whilst backward facing ramps and steps predict very
+                  weak changes in the disturbance development. This is
+                  contrary to the wider literature and an argument is
+                  made that backward facing steps and ramps initiate
+                  an immediate non-linear interaction which cannot be
+                  captured with linear theory. Vertical forward facing
+                  step cases also predict greater amplification with
+                  increased step height, which is not observed in the
+                  backward facing step cases. Again, this is believed
+                  to be due to non-linear mode interaction that is
+                  immediately triggered by the step. Bump roughness
+                  cases agree well qualitatively with experimental
+                  work on a 40 degree swept wing, the AERAST
+                  geometry. Good agreement locally to the roughness
+                  could not be drawn with the NekLNS solutions, likely
+                  due to the presence of strong stream-wise gradients
+                  and mesh limitations.}
 }
 
 @inproceedings{mejia-2020,