An optimal path to transition in a duct

This paper is concerned with the transition of the laminar flow in a duct of square cross-section. Like in the similar case of the pipe flow, the motion is linearly stable for all Reynolds numbers, rendering this flow a suitable candidate for a study of the 'bypass' path to turbulence. It has already been shown \citep{Biau_JFM_2008} that the classical linear optimal perturbation problem, yielding optimal disturbances in the form of longitudinal vortices, fails to provide an 'optimal' path to turbulence, i.e. optimal perturbations do not elicit a significant nonlinear response from the flow. Previous simulations have also indicated that a pair of travelling waves generates immediately, by nonlinear quadratic interactions, an unstable mean flow distortion, responsible for rapid breakdown. By the use of functions quantifying the sensitivity of the motion to deviations in the base flow, the 'optimal' travelling wave associated to its specific defect is found by a variational approach. This optimal solution is then integrated in time and shown to display a qualitative similarity to the so-called 'minimal defect', for the same parameters. Finally, numerical simulations of a 'edge state' are conducted, to identify an unstable solution which mediates laminar-turbulent transition and relate it to results of the optimisation procedure

Transition to turbulence in duct flow

The transition of the flow in a duct of square cross-section is studied. Like in the similar case of the pipe flow, the motion is linearly stable for all Reynolds numbers; this flow is thus a good candidate to investigate the 'bypass' path to turbulence. Initially the so-called 'linear optimal perturbation problem' is formulated and solved, yielding optimal disturbances in the form of longitudinal vortices. Such optimals, however, fail to elicit a significant response from the system in the nonlinear regime. Thus, streamwise-inhomogeneous, sub-optimal disturbances are focussed upon; nonlinear quadratic interactions are immediately evoked by such initial perturbations and an unstable streamwise-homogeneous large amplitude mode rapidly emerges. The subsequent evolution of the flow, at a value of the Reynolds number at the edge between fully developed turbulence and relaminarization, shows the alternance of patterns with two pairs of large scale vortices near opposing parallel walls. Such edge states bear a resemblance to optimal disturbance

The purpose and role of product standards in the commercialization of new energy technologies : a preliminary analysis

This paper discusses the role of product standards in a commercialization program. The usefulness of standards is explained as arising from the existence of transaction costs and other market failures in the operation of markets, and the effects of standards upon market operation are broadly discussed. The role of standards in a commercialization program is then explored and is seen as justified by the existence of market failures and the lack of suitable options other than standards available for remedying certain particulars of the situation. A description of the voluntary standards system follows to show how its use in a commercialization program may modify the governmental role

Comments on proposed rulemaking concerning electric rates for solar users

Energy Laboratory Utility Systems Program

The transition from ias 39 to ifrs 9: main impacts on the Banking industry

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Standards, warranties and commercialization of new energy technologies

Photovoltaics ProjectSeveral federal energy programs aim to "commercialize" new energy tech- nologies, i.e., to bring them from research to the market. Product standards and warranties are sometimes a part of these programs. Yet the benefits which the standards and warranties are to achieve are rarely articulated, and how these benefits will be achieved is often even less clear. This article takes the view that the substantive goals of standards and warranties can be articulated. It examines the functions of standards and warranties and the processes which produce them, and casts their effects in terms of impacts upon the new technology's demand, supply and industrial market structure. The relevance of these impacts upon commercialization programs is then discussed, covering the role of standards in the new in- dustry's development, the need for standards and warranties in demonstration projects and in the private financing of new energy systems, and mechanisms for development of standards and warranties. The need for basic research on standards and warranties is then addressed