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ISSN オンライン: 2642-0554

ENERGY TRANSFER BETWEEN POD MODES OF FORCED TURBULENT FLOW OVER A FENCE

Alexander Orellano
Institut für Strömungsmechanik und Aerodynamik, LRT/WE7 Universität der Bundeswehr München, D-85577 Neubiberg, Germany

Jens Neumann
Institut für Strömungsmechanik und Aerodynamik, LRT/WE7 Universität der Bundeswehr München, D-85577 Neubiberg, Germany

Hans Wengle
Institut für Strömungsmechanik und Aerodynamik, LRT/WE7 Universität der Bundeswehr München, D-85577 Neubiberg, Germany

要約

From large-eddy simulations of unforced and forced turbulent boundary layer flow over a surface-mounted fence of height h (Reh = 3000) samples in time have been collected. These samples (snapshots) of the flow field have been used to carry out three-dimensional proper orthogonal decompositions (POD), in order to extract the dominating spatio-temporal structures of the flow.
The energy balance equation for an individual mode can be derived using a Galerkin projection of the Navier Stokes equation onto the POD modes. These POD modes have also been utilized to evaluate the nonlinear energy transfer terms. It can be concluded that the (high-frequency) roll-up process in the separated shear layer receives most of the energy from the mean flow and exchanges little energy with the other modes. In comparison to this, the (low-frequency) shedding of large-scale structures from the recirculation bubble receives larger amounts of energy from the mean flow and in addition, exchanges one order of magnitude larger amounts of energy with the 'neighbouring' modes. This also explains why, in our flow case, the low-frequency forcing (with Str = 0.08) leads to a much stronger reduction of the mean re-attachment length (36%) than the high-frequency forcing (with Str = 0.60).