The UMIST-N Near-Wall Treatment Applied to Periodic Channel Flow

CHAPTER 6. CONCLUSIONS & SUGGESTIONS FOR FUTURE WORK85
further optimised or simply expanded by the incorporation of other turbu-
lence models within the subgrid. This work has applied the k-ω model to the
subgrid. A further attempt was made to mix a k-ω subgrid with a k-ε main
grid, but the development effort was stopped when it became clear that dif-
ferences in the predicted values of k would necessitate the use of a blending
function similar to that used by the SST [42].
Building upon the use of k-ω, future work could be directed towards the
use of simpler turbulence models, particularly a one-equation model and an
algebraic model within the subgrid. If this can be done while retaining a
k-ε treatment in the main grid, then the adapted subgrid would offer an
additional level of flexibility in the cost/accuracy tradeoff associated with it.
Furthermore, the UMIST-N wall function could be applied to a further va-
riety of flows. Most notably, higher Reynolds numbers could be considered.
There is a difficulty in obtaining DNS results at higher Reynolds numbers,
but perhaps the completion of this work will allow the subgrid approach to
be confidently compared to experiments for periodic flow at higher Reynolds
numbers. Also, this work applies the subgrid treatment to periodic flow at
a relatively low frequency of oscillation and without sufficient amplitude to
generate flow reversal. A higher frequency and a larger amplitude would
provide an interesting test case, provided that suitable data can be found
for comparison. Such a test case would advise as to the applicability of
UMIST-N to the flow inside engines.
In a two-dimensional grid, the UMIST-N method involves simultaneously
storing subgrid results throughout the flow field. In addition to a storage
cost, this presents an added complexity in the implementation of the method.