Polymer Maximum Drag Reduction: A Unique Transitional State

The upper bound of polymer drag reduction is identified as a unique transitional state between laminar and turbulent flow corresponding to the onset of the nonlinear breakdown of flow instabilities

On the role of pressure in elasto-inertial turbulence

The dynamics of elasto-inertial turbulence is investigated numerically from the perspective of the coupling between polymer dynamics and flow structures. In particular, direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 are used to study the formation and dynamics of elastic instabilities and their effects on the flow. Based on the splitting of the pressure into inertial and polymeric contributions, it is shown that the polymeric pressure is a non-negligible component of the total pressure fluctuations, although the rapid inertial part dominates. Unlike Newtonian flows, the slow inertial part is almost negligible in elasto-inertial turbulence. Statistics on the different terms of the Reynolds stress transport equation also illustrate the energy transfers between polymers and turbulence and the redistributive role of pressure. Finally, the trains of cylindrical structures around sheets of high polymer extension that are characteristics of elasto-inertial turbulence are shown to be correlated with the polymeric pressure fluctuations

Sustainable transformation of energy systems in MENA countries : comparative report

A clear understanding of socio-technical interdependencies and a structured vision are prerequisites for fostering and steering a transition to a fully renewables-based energy system. To facilitate such understanding, a phase model for the renewable energy (RE) transition in the Middle East and North Africa (MENA) countries has been developed and applied to ten countries: Algeria, Egypt, Iraq, Israel, Jordan, Lebanon, Morocco, Palestine, Tunisia, and Yemen. This report synthesises the results of these ten studies. The analysis shows that the state of the energy sector in the MENA region varies from country to country, but some underlying trends are present in all countries. In the majority of countries, energy prices are subsidised, and energy markets are mostly not liberalised. The energy demand in all analysed countries is growing and most grid systems are poorly interconnected across borders. Still, the expansion of RE in the MENA region can benefit from significant global progress and cost reductions in RE technologies. Reducing greenhouse gas (GHG) emissions is not the only key driver for energy transition. In fact, the main motives for transition are that RE can help to meet growing demand, reduce dependence on imports, increase energy security, and provide opportunities for economic development. All countries studied have RE targets. While some countries are on track to meet these targets, others need to increase their efforts to expand renewable electricity generation in order to meet their goals. Strong progress has been made in countries with limited fossil energy resources, while in some countries that produce and export large amounts of fossil energy resources, the energy transition is progressing rather slowly

Sustainable transformation of Tunisia's energy system : development of a phase model

A clear understanding of socio-technical interdependencies and a structured vision are prerequisites for fostering and steering a transition to a fully renewables-based energy system. To facilitate such understanding, a phase model for the renewable energy (RE) transition in the Middle East and North Africa (MENA) countries has been developed and applied to the country case of Tunisia. It is designed to support the strategy development and governance of the energy transition and to serve as a guide for decision makers. The analysis shows that Tunisia has already taken important steps towards a RE transition. According to the MENA phase model, Tunisia can be classified as being in the "Take-Off Renewables" phase. Nevertheless, natural gas still plays the dominant role in Tunisia's highly subsidised electricity generation. In addition to the elevated political uncertainty, there are numerous structural, political, social, and economic challenges within the energy sector that hinder progress in the transition to REs. Strong support at all levels is needed to promote the breakthrough of RE. This includes more detailed long-term planning and improving the regulatory framework, as well as reducing offtaker risks to improve the bankability of RE projects in order to attract private investment. Furthermore, institutional buy-in needs to be increased and the engagement of key non-state stakeholders must be strengthened. In light of the growing domestic energy demand and with the on-going global decarbonisation efforts in favour of sustainable fuels, Tunisia would be well advised to embark on a sustainable energy path sooner rather than later to seize economic opportunities that can arise from RE development

Sustainable transformation of Iraq's energy system : development of a phase model

A clear understanding of socio-technical interdependencies and a structured vision are prerequisites for fostering and steering a transition to a fully renewables-based energy system. To facilitate such understanding, a phase model for the renewable energy transition in MENA countries has been developed and applied to the country case of Iraq. It is designed to support the strategy development and governance of the energy transition and to serve as a guide for decision makers. The transition towards renewable energies is still at a very early stage in Iraq. Despite the drop in renewable technology costs over the last decade and the increasing deployment of renewables in the MENA region, the pathway towards renewable energies seems to be challenging for Iraq. This is attributable to the country's political instability and the dominant economic role played by the fossil fuel sector. The most pressing concern for Iraq's electricity sector is the need to secure a constant electricity supply. At operational level, Iraq's electricity infrastructure requires significant investment to rebuilt, retro-fit and expand its overall capacity and to improve efficiencies. Yet, the need to rebuild the energy system after the war and the subsequent violent conflicts could offer an opportunity for a transition towards renewables that would benefit Iraq in the short term and also provide a long-term economic development perspective. To take advantage of this opportunity, Iraq needs to improve the framework conditions for renewable energies and raise awareness about the benefits it offers. Renewable energy regulations need to be introduced, market development supported, a realistic timeframe for the transition process established and an appropriate and reliable legal framework developed. The results of the analysis along the transition phase model towards 100% renewables are intended to stimulate and support the discussion about Iraq's future energy system by providing an overarching guiding vision for the energy transition and the development of appropriate policy strategies

Radiation Modeling of a Hydrogen-Fueled Scramjet

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90696/1/AIAA-2011-3769-521.pd

Full-system RANS of the HyShot II scramjet Part 1: Numerics and non-reactive simulations

Predictive Science Academic Alliance Program (PSAAP

Sustainable transformation of Egypt's energy system : development of a phase model

A clear understanding of socio-technical interdependencies and a structured vision are prerequisites for fostering and steering a transition to a fully renewables-based energy system. To facilitate such understanding, a phase model for the renewable energy transition in MENA countries has been developed and applied to the country case of Egypt. It is designed to support the strategy development and governance of the energy transition and to serve as a guide for decision makers. Egypt, with its abundant solar and wind energy potential, has excellent preconditions to embark on the pathway towards a 100% renewable energy system. The country has successfully taken its first steps in this direction by attracting international finance and implementing several large-scale solar and wind projects. Yet, while Egypt has made significant progress, increased efforts are still required if the country aims to proceed towards a fully renewables-based system. The stronger system integration of renewable energies requires, for example, an alignment of regulations for the electricity, mobility and heat sectors. In this context, Egypt would be well advised to develop and implement an overall strategy for the energy transition that includes not only electricity generation but all sectors. By placing a stronger focus on renewable energy, also to decarbonise the industrial sector, Egypt, as Africa's second most industrialised country, could seize the opportunity for economic development within a decarbonising global economy. The results of the analysis along the transition phase model towards 100% renewable energy are intended to stimulate and support the discussion on Egypt's future energy system by providing an overarching guiding vision for the energy transition and the development of appropriate policies