The Centre for ECO2 Vehicle Design (ECO2) is a Swedish multilateral competence centre based at KTH Royal Institute of Technology with a focus on the development of resource effcient vehicle for sustainable transport. This report covers the first 18 months of ECO2’s new agreement period (Jul 2024 – Dec 2029), marking a period of organizational renewal, research excellence, and strategic positioning for future growth. During this period, ECO2 successfully completed three PhD defences, produced 33 peer-reviewed journal publications, 50 conference papers, and strengthened its research portfolio with 12 projects multiple project applications. The new five-year centre agreement was finalized, securing partner and KTH financing co-financing and establishing enhanced governance structures. ther highlights include the holding of the second Resource Efficient Vehicles conference in Graz with 10 ECO2 contributions, establishing a collaboration agreement with Fraunhofer IAO, and expanding industrial partnerships through new doctoral projects. ECO2’s research continues to address critical attributes of vehicles as part the transport system – effciency, accessibility and resilience, which contribute sustainable transport and other major societal challenges.

The usage of perforated plates in passive noise-control systems in e.g. aircraft liners and mufflers involves the standard operating conditions of grazing flow and high-amplitude acoustic incidence. This study focuses on the usage of the three-port experiment technique for the experimental passive acoustic characterisation of a perforated plate. Expanding on the previous paper about the resistance of the perforate, the influence of operating conditions on the imaginary part of the transfer impedance, i.e., the reactance is discussed here. The relationship between the end correction in the linear range, without the presence of grazing flow, and the frequency of acoustic excitation is demonstrated. The reduction in the value of the mass end correction under the individual effects of grazing flow, and high-amplitude excitation is presented. Additionally, depending on the excitation wavelength, the partial recovery of the reduced value of the end correction under simultaneous exposure is also shown. Using the experimental results, models for the end correction, and by extension the reactance are proposed. These models take into account the geometrical parameters of the perforate, and the dimensionless Mach, Shear and Strouhal numbers.

Sound reducing treatment in for instance aircraft engine and IC engine applications often involve the use of perforates. In these applications they are exposed to fluid flow and high-level acoustic excitation, and this influences the acoustic properties of the perforate, as is well known from many published papers. The acoustic properties are usually described using a transfer impedance. The transfer impedance of a perforate sample has been studied using both a conventional impedance tube (two-port) setup and an innovative three-port setup. The three-port configuration made it possible to study both the effect of grazing flow and high-level excitation effects separately as well as jointly. In the present paper these recent experimental results are presented and comparisons are made with results from previously published papers and empirical models.

This study introduces an agent-specific assessment method of traffic noise exposure in agent mobility simulations. The assessment is achieved through a combination of an energy-based noise exposure impact assessment using noise exposure cost, and the state-of-the-art traffic noise prediction tool NoiseModelling coupled with the activity-based agent mobility simulation software MATSim. The agent-specific noise exposure cost is a measure to evaluate how the noise emissions from the transport of agents relate to the noise-related impact on other agents performing stationary activities. By introducing an agent-specific level, each agent’s individual responsibility for the noise exposure may be estimated. The potential of the agent-specific noise exposure cost concept, combined with the MATSim-NoiseModelling framework, is illustrated through a case study, applying activity-based agent mobility simulations across Nantes, France. The results of the case study highlight, among other considerations, the insights that an agent-specific, activity-based noise exposure cost approach provides by visualizing the noise exposure ”footprint” resulting from an agent’s transportation activities.

Perforates are frequently used as part of sound reducing treatment in for instance aircraft engine and IC engine applications. In these applications they are exposed to fluid flow and high-level acoustic excitation, and this influences the acoustic properties of the perforate, as is well known from many published papers. The acoustic properties are usually described using a transfer impedance. The transfer impedance of a perforate sample has been studied using both a conventional impedance tube (two-port) setup and an innovative three-port setup. The three-port configuration made it possible to study both the effect of grazing flow and high-level excitation effects separately as well as jointly. The present paper concentrates on the nonlinear effects. Comparisons are made with results from previously published papers and empirical models.

The flow over circular cylinders or tubes arranged in different configurations is widely employed in various engineering applications, ranging from combustion systems to HVAC systems. The Reynolds number serves as the governing parameter defining the flow around the cylinders, determining the separation of the flow from the cylinder surface, and establishing a separation point. This separation point, in turn, dictates the formation of a jet with parameters such as jet height, jet velocity, and jet length. The jet formation, influenced by varying Reynolds numbers, introduces the possibility of various characteristic lengths, including the diameter of the cylinders, height of the duct, gap between adjacent cylinders, jet height, and jet length. This study aims to explore the profound influence of these characteristic lengths on the aeroacoustic properties and the flow acoustic coupling at cylinders in cross flow. The jet parameters are derived from the analysis of experimental and analytical modeling data. Through a systematic investigation, we examine the interdependencies between these characteristic lengths and the resulting aeroacoustic properties.

Collapsible tubes can be employed to study the sound generation mechanism in the human respiratory system. The goals of this work are (a) to determine the airflow characteristics connected to three different collapse states of a physiological tube and (b) to find a relation between the sound power radiated by the tube and its collapse state. The methodology is based on the implementation of computational fluid dynamics simulation on experimentally validated geometries. The flow is characterized by a radical change of behavior before and after the contact of the lumen. The maximum of the sound power radiated corresponds to the post-buckling configuration. The idea of an acoustic tube law is proposed. The presented results are relevant to the study of self-excited oscillations and wheezing sounds in the lungs.

Perforated plates are frequently applied in passive noise-control systems in e.g. aircraft liners and mufflers. Many of the applications of a perforated plate involve an exposure to grazing flow and high-amplitude acoustic incidence. The ongoing scientific effort of providing experimental results using multiform test setups is continued in this study. Incorporating the three-port technique, the passive acoustic response of a perforated plate is studied under acoustic excitation from three directions in presence of grazing flow and high-amplitude acoustic excitation. The applied three-port technique has an advantage of being a direct method for impedance determination and is not bound by any boundary conditions traditionally considered in presence of grazing flow. In this study, a semi-empirical model for the normalised resistance of a perforate is presented. The model takes the Mach, Strouhal, and Shear numbers into account. Additionally, for low grazing flow speeds, the non-linear effects of resistance are found to be dependent on the grazing flow speed.

Perforates are frequently used as part of sound reducing treatment in for instance aircraft engine and IC engine applications. In these applications they are exposed to fluid flow and high-level acoustic excitation, and this influences the acoustic properties of the perforate, as is well known from many published papers. The acoustic properties are usually described using a transfer impedance. In a previous part of this study the effect on the real part (resistance) of the transfer impedance was studied using both a conventional impedance tube (two-port) setup and an innovative three-port setup. The three-port configuration made it possible to study both the effect of grazing flow and high-level excitation effects separately as well as jointly. The present paper is a follow-up study where the imaginary part (reactance) of the transfer impedance is the focus. Comparisons are made with results from previously published papers and empirical models.

Flexible tubes are simple yet powerful tools for the modeling of respiratory and circulatory systems [1, 2]. In the last decade, access to high-performance computational resources has allowed the implementation of realistic numerical models of human vessels based on Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) simulations. Interestingly, the recently proven correlation [3] between CFD observables (like the pharyngeal airway's resistance) and clinical data (such as the Apnoea Hypopnea Index in Obstructive Sleep Apnoea patients) suggests a possible development of diagnostic methods based on numerical simulations. This work aims to investigate the extension of these correlations to the aeroacoustics characteristics of flexible conduits by means of a fully coupled FSI numerical model based on the Large Eddy Simulation method. These results have relevant applications to studying diseases of the human upper vocal tract, voice production, obstructive sleep apnoea, and adventitious lung sounds, such as wheezing and crackling.

[1] Grotberg, J. B., & Jensen, O. E. (2004). Annu. Rev. Fluid Mech., 36, 121–147.

[2] Schwartz, A. R., & Smith, P. L. (2013). The Journal of Physiology, 591(Pt 9), 2229.

[3] Schickhofer L., Malinen J., Mihaescu M., J. Acoust. Soc. Am. - JASA, 145 (4): 2049–2061, 2019. https://doi.org/10.1121/1.5095250