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Item type:Publication, Access status: without files , The physics of stripe patterns in turbulent channel flow determined by DNS resultsThe turbulent flow in an infinitely extended plane channel is analysed by solving the Navier-Stokes equations with a DNS approach. Solutions are obtained in a numerical solution domain of finite size in the streamwise as well as in the lateral direction setting periodic boundary conditions in both directions. Their impact on large scale structures in the turbulent flow field is analysed carefully in order to avoid their suppression. When this is done appropriately well known stripe patterns in these flows can be observed and analysed especially with respect to their relative motion compared to the mean flow velocity. Various details of this stripe pattern dominated velocity field are shown. Also global parameters like the friction factor in the flow field and the Nusselt number in the temperature field are determined based on the statistics of the flow and temperature data in a very large time period that guarantees fully developed turbulent flow and heat transfer.Publicationtype: Journal Article100 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Natural convection in a vertical plane channel : DNS results for high Grashof numbersThe turbulent natural convection of a gas (Pr = 0.71) between two vertical infinite walls at different but constant temperatures is investigated by means of direct numerical simulation for a wide range of Grashof numbers (6.0 × 106 > Gr > 1.0 × 103). The maximum Grashof number is almost one order of magnitude higher than those of computations reported in the literature so far. Results for the turbulent transport equations are presented and compared to previous studies with special attention to the study of Verteegh and Nieuwstadt (Int J Heat Fluid Flow 19:135-149, 1998). All turbulence statistics are available on the TUHH homepage (http://www.tu-harburg. de/tt/dnsdatabase/dbindex.en.html). Accuracy considerations are based on the time averaged balance equations for kinetic and thermal energy. With the second law of thermodynamics Nusselt numbers can be determined by evaluating time averaged wall temperature gradients as well as by a volumetric time averaged integration. Comparing the results of both approaches leads to a direct measure of the physical consistency.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A critical analysis of turbulent natural and forced convection in a plane channel based on direct numerical simulationThe balance equations for mixed convection in plane channel flow, based on the Boussinesq assumption for buoyancy, are carefully analysed by considering the two limits of pure forced and natural convection. Additional information about the flow is gained from the mechanical energy equation and the entropy equation (the second law of thermodynamics). Since the Boussinesq approximation assumes ε = δT*/T* → 0, i.e. a vanishing dimensionless temperature difference between the hot and the cold wall, certain inconsistencies in modelling the flow appear for ε ≠ 0. They are identified and discussed with respect to their importance. Numerical solutions gained by a direct numerical simulation (DNS) approach give detailed information about the friction factors and Nusselt numbers including the influence of those terms in the equations that turn out to be the source of the inconsistency in the modelling for ε ≠ 0. © 2011 Taylor and Francis Group, LLC.Publicationtype: Journal Article13