A transformation that relates a compressible wall-bounded turbulent flow with nonuniform fluid properties to an equivalent incompressible flow with uniform fluid properties is derived and validated. The transformation accounts for both variable-property and intrinsic compressibility effects, the latter being the key improvement over the current state of the art. The importance of intrinsic compressibility effects contradicts the renowned Morkovin's hypothesis.

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The purpose of this paper is to investigate and compare in what ways different types of integrative and collaborative procurement strategies may enhance efficiency and innovation in public infrastructure projects. Further, implementation challenges are identified and discussed. Interview-based case studies were performed of ten infrastructure projects in Sweden and the Netherlands. The projects involve four types of collaborative procurement strategies - collaborative Design-Build (DB) contracts, Early Contractor Involvement (ECI) agreements, Design-Build-Maintain (DBM) contracts and Design-Build-Finance-Maintain (DBFM) contracts. The findings indicate that the duration of the collaboration is fundamental in setting the limits for innovation and that early involvement as well as long-term commitments open up for more innovation. Naturally, the potential for increased efficiency is higher than for innovation and also occurs in collaborations with limited duration. These integrated project approaches, however, still appear to be in an early stage of learning. For a public repeat client to realise the full potential of a new strategy, it is important to have a long-term perspective and capabilities to analyse and learn from the experiences.

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The purpose of this paper is to investigate and compare in what ways different types of integrative and collaborative procurement strategies may enhance efficiency and innovation in public infrastructure projects. Further, implementation challenges are identified and discussed. Interview-based case studies were performed of ten infrastructure projects in Sweden and the Netherlands. The projects involve four types of collaborative procurement strategies - collaborative Design-Build (DB) contracts, Early Contractor Involvement (ECI) agreements, Design-Build-Maintain (DBM) contracts and Design-Build-Finance-Maintain (DBFM) contracts. The findings indicate that the duration of the collaboration is fundamental in setting the limits for innovation and that early involvement as well as long-term commitments open up for more innovation. Naturally, the potential for increased efficiency is higher than for innovation and also occurs in collaborations with limited duration. These integrated project approaches, however, still appear to be in an early stage of learning. For a public repeat client to realise the full potential of a new strategy, it is important to have a long-term perspective and capabilities to analyse and learn from the experiences.@en

We derive and analyze a model for implicit Large Eddy Simulation (LES) of compressible flows that is applicable to a broad range of Mach numbers and particularly efficient for LES of shock-turbulence interaction. Following a holistic modeling philosophy, physically sound turbulence modeling and numerical modeling of unresolved subgrid scales (SGS) are fully merged, in a manner quite different from that of traditional implicit LES approaches. The implicit subgrid model is designed in such a way that asymptotic consistency with incompressible turbulence theory is maintained in the low Mach number limit. Compressibility effects are properly accounted for by a novel numerical flux function, which can capture strong shock waves in supersonic flows and also ensures an accurate representation of smooth waves and turbulence without excessive numerical dissipation. Simulations of shock-tube problems, Noh's three-dimensional implosion problem, large-scale forced and decaying three-dimensional homogeneous isotropic turbulence, supersonic turbulent boundary layer flows, and a Mach = 2.88 compression-expansion ramp flow demonstrate the good performance of the SGS model; across this range of flows, predictions are in excellent agreement with theory, direct numerical simulations, and experimental reference data. Results for implicit LES of canonical shock-turbulence interaction are compared with results of explicit LES using the dynamic Smagorinsky model. The analysis shows that details of the numerical method used for shock capturing clearly outweigh the effect of different turbulence modeling strategies in explicit and implicit LES. The implicit LES model recovers the ideal 2nd-order grid convergence of shockcapturing errors that has been predicted using Rapid Distortion Theory. The dynamic Smagorinsky model in conjunction with a hybrid method that combines sixth-order central differences with a seventh-order weighted essentially non-oscillatory scheme yields turbulence statistics that are very similar to the implicit LES results. However, while the explicit LES requires a tailored high-order low-dissipative numerical method that applies numerical dissipation only in shock normal direction, no such ad hoc adjustments are necessary with the proposed implicit LES method.

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Wall-models are essential for enabling large-eddy simulations (LESs) of realistic problems at high Reynolds numbers. The present study is focused on approaches that directly model the wall shear stress, specifically on filling the gap between models based on wall-normal ordinary differential equations (ODEs) that assume equilibrium and models based on full partial differential equations (PDEs) that do not. We develop ideas for how to incorporate non-equilibrium effects (most importantly, strong pressure-gradient effects) in the wall-model while still solving only wall-normal ODEs. We test these ideas using two reference databases: an adverse pressure-gradient turbulent boundary-layer and a shock/boundary-layer interaction problem, both of which lead to separation and re-attachment of the turbulent boundary layer.

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The objective of this paper is the analysis and the control of local truncation errors in Large Eddy Simulations. We show that physical reasoning can be incorporated into the design of discretization schemes. Using systematic procedures, a nonlinear discretization method is developed where numerical and turbulence-theoretical modeling are fully merged. The truncation error itself functions as an implicit turbulence model which accurately represents the effects of unresolved turbulence.@en