Joern Huenteler

Influence of the volute on the flow in a centrifugal compressor of a high-pressure ratio turbocharger

Abstract The asymmetric influence of the volute on the flow in a transonic, high-pressure ratio centrifugal compressor at off-design conditions was investigated. Fully three-dimensional viscous steady-state computational fluid dynamics (CFD) was applied to simulate the flow in a 4.2:1 design pressure ratio compressor for automotive application. Computed performance characteristics are presented for low- and high-pressure ratio operating conditions, with and without an overhung volute. The volute was found to severely harm aerodynamic stability of the investigated compressor when operating at lower than design mass flow. The relative narrowing effect of the volute on compressor map width increases with pressure ratio up to a 42 per cent drop in stable flow range at design speed. The inter-passage variations in performance quantities and the influence of the volute tongue region are discussed in detail. The circumferential variations of incidence angle correlate with rotational speed, which, in combination with the higher sensitivity to incidence angle at transonic inflow conditions, seems to deteriorates stability when transonic inflow conditions are reached.

Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetric Flow Control-Part I: Non-Axisymmetrical Flow in Centrifugal Compressor.

This is Part I of a two-part paper documenting the development of a novel asymmetric flow control method to improve the stability of a high-pressure-ratio turbocharger centrifugal compressor. Part I focuses on the nonaxisymmetrical flow in a centrifugal compressor induced by the nonaxisymmetrical geometry of the volute while Part II describes the development of an asymmetric flow control method to avoid the stall on the basis of the characteristic of nonaxisymmetrical flow. To understand the asymmetries, experimental measurements and corresponding numerical simulation were carried out. The static pressure was measured by probes at different circumferential and stream-wise positions to gain insights about the asymmetries. The experimental results show that there is an evident nonaxisymmetrical flow pattern throughout the compressor due to the asymmetric geometry of the overhung volute. The static pressure field in the diffuser is distorted at approximately 90 deg in the rotational direction of the volute tongue throughout the diffuser. The magnitude of this distortion slightly varies with the rotational speed. The magnitude of the static pressure distortion in the impeller is a function of the rotational speed. There is a significant phase shift between the static pressure distributions at the leading edge of the splitter blades and the impeller outlet. The numerical steady state simulation neglects the aforementioned unsteady effects found in the experiments and cannot predict the phase shift, however, a detailed asymmetric flow field structure is obviously obtained.

How a Product's Design Hierarchy Shapes the Evolution of Technological Knowledge – Evidence from Patent-Citation Networks in Wind Power

We analyze how a products design hierarchy shapes the focus of inventive activity and the expansion of the underlying body of knowledge, building on the complex-system perspective on technological evolution. This perspective suggests that the design hierarchy of a product can have an ordering effect on the evolution of commercialized artifacts, in particular when product design decisions on high levels of the design hierarchy set the agenda for subsequent variation and experimentation on lower levels. We extend this literature by analyzing the design hierarchys effect on the evolution of the industrys knowledge base, using the case of wind turbine technology over the period 1973–2009. We assess the technological focus of patents along the core trajectory of knowledge generation, identified through a patent-citation network analysis, and link it to a classification of technological problems into different levels in the design hierarchy. Our analysis suggests that the evolution of an industrys knowledge base along a technological trajectory is not a unidirectional process of gradual refinement: the focus of knowledge generation shifts over time between different sub-systems in a highly sequential pattern, whose order is strongly influenced by the design hierarchy. Each of these shifts initiates the integration of new domains of industry-external knowledge into the knowledge base, thus opening windows of competitive opportunity for potential entrants with strong knowledge positions in the new focus of inventive activity. We discuss implications for the understanding of the competitive advantage of specific knowledge positions of firms and nations and technology policy for emerging technologies.

Creating Markets for Energy Innovations - Case Studies on Policy Design and Impact (Dissertation Synopsis)

The urgency of the world’s environmental challenges has led governments around the globe to rethink the role of government in the innovation process. In addition to direct public spending on energy technology research, development and demonstration, many countries now subsidize the large-scale deployment of innovative energy technologies through so-called ‘deployment policies’. Examples include feed-in tariffs for renewable electricity, mandates for the blending of biofuels and investment subsidies for electric vehicles. Deployment policies can be expensive ways to mitigate the current environmental footprint of the energy system, but proponents justify them as ‘learning investments’ which will pay off in the long term as they stimulate innovation, bring down cost and enhance the performance of clean energy technologies for future generations. The debate on the validity of this claim is controversial and politicized, in part because the discussion often lumps together very different technologies and paints a simplified picture of the complex process of system transformation. This thesis presents six essays to advance this debate, three on the nature of the innovation process in different energy technologies and three on the design and governance of deployment policy instruments. Collectively, these essays make three distinct contributions.First, this thesis introduces a novel methodology to study the evolution of technology. A combination of patent content analysis and citation-network analysis, the method developed in this thesis allows to quantitatively study the focus of research activity in a sector over time and across geographies. In the future, this methodology will allow to study a number of under-researched phenomena in the evolution of technology, including (i) the relationship between the focus of research activity and competitive advantage; (ii) the division of labor in research and development between countries and regions in global value chains; (iii) the impact of public policy on shifts in the focus of research activities.Second, this thesis introduces the explicit consideration of differences in the innovation process between energy technologies into the analysis of deployment policies. It shows that the model of the technology life-cycle that is implicitly assumed in much of the current debate on deployment policies applies to mass-produced energy technologies, but does not adequately describe innovation in complex infrastructure technologies in the energy sector. This is important because different models of the life-cycle imply different roles for deployment – and thus deployment policies – in the evolution of technology. It means that the conceptual underpinnings of the debate on deployment policies do not apply to a significant share of the energy technology space, and calls for the explicit consideration of technological characteristics in decisions on deployment policy support for energy technologies, in particular the size, duration and geographical scope of support. It also allows us to reconcile conflicting evidence on the impact of deployment policies in the literature. These findings are based on three case studies in the first three essays of the thesis: (1) an analysis of the focus of inventive activity over time in wind turbine technology in 1973-2009, using a novel methodology that integrates expert assessment of patent data with patent-citation network analysis; (2) a comparison of technology life-cycles in wind turbine technology and solar PV technology in 1970-2009, using the same methodology; and (3) a techno-economic model of the impact of local and global learning on the cost of renewable energy deployment in Thailand in 2013-2021.Third, this thesis’ results emphasize the need to consider the complex political dynamics of socio-technical transformations in the debate on energy innovation policies in general and deployment policies in particular. In most technology policy analyses, policy decisions are seen as essentially exogenous to the technological change the intervention aims to induce. In practice, this means that the possibility of changes to public policy in response to induced technological change is not part of the analysis, nor is the ability of affected actors to foresee or respond to such changes. Essay 4 demonstrates that this may not adequately reflect political reality. The essay presents a qualitative analysis of the evolution of Germany’s public policy support for solar power in 2000-2012. The essay demonstrates that deployment policy instruments can become at least in part endogenous to the transformation they were designed to induce, because they trigger unforeseen changes in the socio-technical system, and develops a model to account for these dynamics. The findings have two important implications. First, because investors in innovative energy technologies are aware of the possibility of policy changes, the effect of deployment policies on innovation will depend, at least in part, on the political system and its ability to learn and respond. Second, the ability of a policy to induce desired technological outcomes will depend as much on the design of the policy itself as on the state of the socio-technical system. Policy designs and lessons learned can therefore not always be transferred between jurisdictions – e.g., the fact that Germany may no longer need costly feed-in tariffs to attract investment in photovoltaics does not mean this policy is not the most cost-efficient option to attract investment in other jurisdictions. The last two essays explore these two implications in more detail. Essay 5 reviews and analyzes the proposals for internationally supported feed-in tariffs for renewable energy in developing countries, and discusses how to minimize the risk premium demanded by investors due to the policy risk induced by the prospect of unforeseen cost developments. Essay 6 explores the implications of the German experience with deployment policies for solar power in the context of the newly introduced feed-in tariff for renewable electricity in Japan.

A Heuristic for Technology Strategies in Post-Kyoto Bottom-Up Climate Policy

The recent UNFCCC conferences starting with Bali in 2007 until Lima in 2014 have paved the way for the integration of nationally determined initiatives into the global climate governance architecture. National ‘green growth’ strategies have become a new paradigm for policymakers and executives. Designed with the aim of decoupling economic development from adverse environmental impacts, these bottom-up policies hold the promise of overcoming the gridlock in international climate negotiations. Building on the literature on innovation research, this paper contributes to the understanding of technology strategies in the context of nationally appropriate mitigation actions (NAMAs) under the UNFCCC. It is evident that NAMAs aiming to create domestic industries by leveraging technological innovation must consider the characteristics of the targeted technology. Working from this notion, this paper proposes a heuristic to differentiate between four distinct types of technologies. Each type features specific forms of technological learning, value chain constellations and modes of technology transfer. We illustrate the four types using the cases of small hydro, wind turbines, electric vehicles and solar cells and discuss methodologies to classify further technologies ex-ante. We argue that the heuristic captures essential technological characteristics that NAMAs and international support mechanisms need to consider. The different forms of technological learning and value chain constellations are relevant for a country’s choice of technological priorities, while the modes of technology transfer can inform strategies for implementation and international cooperation. We discuss technology-specific strategies for developing countries at different stages of development and international institutions such as the Green Climate Fund and the new Technology Mechanisms under the UNFCCC.