Contribution
Controlling entrainment in the smoke cloud using level set-based front tracking
Dietze, Eckhard; Schmidt, Heiko; Stevens, Bjorn; Mellado, Juan Pedro
Meteorologische Zeitschrift Vol. 23 No. 6 (2015), p. 661 - 674
32 références bibliographiques
publié: Jan 13, 2015
publication en ligne: Nov 14, 2014
manuscrit accepté: Jul 24, 2014
révision final du manuscrit reçu: Jul 23, 2014
révision du manuscrit demandée: Apr 19, 2014
manuscrit reçu: Feb 28, 2014
Open Access (article peut être télechargé gratuitement)
Abstract
Although large-eddy simulation (LES) has been shown to produce a reasonable representation of the turbulent circulations within the stratocumulus-topped boundary layer, it has difficulties to accurately predict cloud-top entrainment rates. In this paper, we present a front-tracking algorithm for LES to untangle the numerical and physical contributions to entrainment. Instead of resolving the cloud-top inversion, we treat it as a discontinuity separating the boundary layer from the free atmosphere and use the level set method to track its location. We apply our method to the smoke cloud test case as presented by Bretherton et al. (1999) which is simpler than stratocumulus in that it is only driven by radiative cooling avoiding evaporative feedbacks on entrainment. We present three-dimensional LES results with and without use of the level set method varying the grid resolution and the flux limiter. With the level set method, we prescribe zero entrainment and use this case to evaluate our method's ability to maintain a non-entraining smoke-cloud layer. We use an empirically-based entrainment law to estimate numerical errors. With the level set method, the prescribed entrainment rate was maintained with errors about one order of magnitude smaller than the entrainment errors found in the standard LES. At the same time, the dependence of the entrainment errors on the choice of the limiter was reduced by more than a factor of 10.
Mots-clefs
Entrainment • Stratocumulus • Large-eddy simulation • Level set method