Near-Critical Orographic Forcing Of Stratified Flow
| Project acronym: | HIII-CNRS21_Toulouse_JohnsonOrographicForcing |
| Name of Group Leader: | Pr. E.R. Johnson, Department of Mathematics, UCL, U.K.,
E-mail: e.johnson@ucl.ac.uk Dr. G. Esler, Department of Mathematics, UCL, U.K., E-mail: gavin@math.ucl.ac.uk |
| User-Project Title: | Near-Critical Orographic Forcing Of Stratified Flow |
| Facility: | Stratified Flume |
| Proceedings TA Project: | Near-critical orographic forcing of stratified flow |
| Data Management Report: | Data Management Reports Page You will need to login to view this page |
Summary:
Two inter-related aspects of flow over orography have proved difficult to model simply -- the structure of the flow-field and the pressure drag exerted on the oncoming flow – yet these are of great interest. Rising and falling air affects cloud cover and rainfall distribution, and drag is of particular importance to oceanographers, climate modellers and esearchers involved in the development of numerical weather-prediction models, because of the need to parameterize the drag exerted by orography with spatial scales below the model grid scale.
Analytical studies show that the dynamics of the flow of two fluid layers of almost equal depths and densities differs significantly from those where the densities are similar but the depths differ. In particular, the waves that appear behind isolated three-dimensional orography in near-critical, but slightly subcritical, flow are long compared to the obstacle dimensions and stretch laterally across the flow with little change of form.
Our results show that these aspects of the wake can be observed experimentally. The experiments have been done in the CNRM-GAME (CNRSToulouse) stratified water flume, using an optical measurement technique developed at IMFT and a drag measurement technique developed at CNRMGAME. This unique facility is indeed very pertinent for such a study, in particular due to its ability to generate density stratified flow at high Reynolds numbers with low confinement effect.
Fig. 1 Experimental set-up at the
CNRS-Toulouse stratified water
flume
Fig. 2 The two-dimensional interface
displacement pattern in the tank for an
experiment with Fr=1.08, just after the obstacle
left the field of view. X-axis is along the flow
(and flume main axis, center of the obstacle
is close to X~130cm, below the figure Y-axis).
Y-axis is perpendicular to the flow (center of the
obstacle and flume axis are close to Y~135cm).
Flow is going from the bottom to the top.
| Publication References |
| Esler J.G., Rump O.J., Johnson E.R. (2005): Steady rotating flows over a ridge. Physics of Fluids 17(11): 116601. |
| Esler J.G., Rump O.J., Johnson E.R. (2007): Transcritical rotating flow over topography. Journal of Fluid Mechanics 590, 81--106. |
| Johnson E.R., J.G. Esler, A. Paci, S. Cazin, E. Cid, O. Eiff and L. Lacaze (2010): Near-critical orographic forcing of stratifier flow, proceedings of HYDRALAB-III Joint User Meeting. |
| Johnson, E.R., and G.G. Vilenski (2004): Flow Patterns and Drag in Near-Critical Flow over Isolated Orography. J. Atmos. Sci., 61, 2909–2918. |
| Johnson E.R. and G.G. Vilenski (2005): Two-dimensional leaps in near-critical flow over isolated orography. Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences 461(2064): 3747. |
| Johnson E.R., Esler J.G, Rump O., Sommeria J., Vilenski G. (2006): Orographically generated nonlinear waves in rotating and non-rotating two-layer flow. Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences 462(2065): 3. |