Lee waves: new understanding of a classical problem

We explore the classical problem of lee wave generation by a stationary isolated three- dimensional obstacle in a uniform low-Froude-number stratified flow. By separating the permanent waves produced into three distinct categories, we compare detailed experimental measurements with theoretical predictions. We pay particular attention to the time-dependent establishment of the wave field and the orientation of the fan of lee waves that is established. As seen by previous authors, we find that the uniform flow can be divided into two regions: an essentially two-dimensional flow around the base of the obstacle and a wave-generating flow over the top portion of the obstacle. We show that quantitative agreement between experimental observations and predictions of linear wave theory is only possible if we take into account a small slope across the obstacle of the surface separating the quasi-two- dimensional flow around the base of the obstacle and the wave-generating flow over the top of the obstacle.