Variational Multiscale Large Eddy Simulation of Turbulent Flow in a Diffuser

Abstract

In the present study, variational multiscale large eddy simulation (LES) is applied to turbulent flow in a diffuser, which represents a challenging test case due to the appearance of flow separation and subsequent reattachment. Two different scale-separating operators based on multigrid operators are used for separating large and small resolved scales. Dynamic as well as constant-coefficient-based subgrid-scale modeling are employed in the variational multiscale LES. The results show that the variational multiscale LES with a simple constant-coefficient Smagorinsky model using a projective scale-separating operator yields a very good prediction of most of the crucial flow features. Furthermore, it turns out to be by far the most computationally efficient approach, resulting in a computing time reduction of about 18% compared to the traditional LES with a dynamic Smagorinsky model. The variational multiscale LES with a dynamic Smagorinsky model does not prove to be a superior approach.

Variational Multiscale Methods for incompressible flows

“…Several features of this flow indicate its higher complexity (i.e., a large unsteady separation bubble due to an adverse pressure gradient, a sudden change of the streamwise pressure gradient from slightly favorable to strongly adverse at the diffuser throat, and a slowly growing internal layer emerging at the upper flat wall in the relaxation zone downstream of the sharp variation in the streamwise pressure gradient). The problem setup and several results from this test case are reported in [5]. The diffuser geometry, which basically matches the experimental configuration in [1] ("Buice-experiment") as well as the numerical setup in [11] ("Wu-LES"), is shown in Fig.…”

“…Since the underlying assumption (i.e., the mutual influence of the small scales is confined to individual elements of an initially chosen discretization) often appears to be too restrictive, we turned to an approach where the interaction of the small resolved scales is not localized in such a way, see [4]. This global variational multiscale approach was applied to turbulent flow in a channel in [4] and turbulent flow in a diffuser in [5]. As outlined above, three different scale groups (i.e., large resolved scales, small resolved scales, and unresolved scales) are distinguished, and the modeled effect of the unresolved scales is directly applied only to the small resolved scales.…”

“…4 depicts the results for the skin Results for further flow parameters can be found in [5]. It is stated that all methods tend to underpredict C f compared to the results from the Wu-LES and the Buice-experiment.…”

“…Using the scale-separating operator SM, the numbers increase drastically for CMS. Less effort is required for PM compared to SM for reasons explained in [4] and [5].…”

Calculation of hydrodynamic noise in the diffuser of a pulsation damper flow channel

“…Как показывает анализ работ, посвящённых исследованию турбулентного течения в каналах [22][23][24][25][26][27][28][29], в расширительной части трубопровода формируются вихревые структуры, являющиеся возможной при-чиной внутреннего шума. Существуют лишь приближённые полуэмпирические модели гидродинамики такого течения.…”