Stratified flow over asymmetric and double bell-shaped obstacles

We performed experiments on quasi-two-dimensional lee-wave formation behind obstacles towed through a linearly stratified fluid. Initial transient times, amplitudes and wavelengths are measured for five different obstacle shapes at several flow velocities. We found that the wave field is determined primarily by the height and the leeward slope of the obstacle, in agreement with previous works. Differences between measured quantities and predictions of linear theories indicate that nonlinear effects are important in our parameter range. Experiments with a twin obstacle gave surprising results: average wavelengths and amplitudes are systematically lower than that of produced by an isolated obstacle, which we attribute to the dominance of essential nonlinearities such as anomalously strong wave dispersion. (C) 2003 Elsevier B.V. All rights reserved.