Reduced order hemodynamic models are an increasingly important complementary tool to in vivo measurements. They enable effective creation of large datasets with well-defined parameter variations, which can be used, for example, for training machine learning models, conducting virtual studies of intervention strategies, or for the development of pulse wave analysis algorithms. Here, a 1D frequency domain formalism for pulse wave propagation in the cardiovascular system is presented. Using the scattering matrix formulation, a computationally efficient and causal solution is obtained, including possible source terms and nonideal coupling conditions. Local nonlinear effects, as those seen in stenoses or aneurysms, are introduced via an iterative procedure, achieving as good accuracy as state-of-the-art time-domain solvers while being significantly more computationally efficient. The new formalism has been successfully validated against well-documented reference cases from the literature.

Axial cooling fans operating downstream of obstructions are often exposed to distorted inlet flow conditions, consequently impacting acoustic performance. Herein the impact of upstream obstructions with simple geometries on the psychoacoustics of an axial fan with rotating ring is investigated. Different loading conditions and inlet shroud lengths are considered, while a reference non-obstructed installation is also recorded. Results showcase significant increase in loudness for obstructed installations at intermediate and free discharge loading conditions irrespective of inlet shroud lengths tested. Sharpness, fluctuation strength and roughness demonstrate no sensitivity to loading conditions for obstructed installations, while tonality levels depend on inlet shroud length.

Low-speed axial fans for engineering cooling applications are often operating in the vicinity of humans. Over the last decades, an effort to mitigate fan noise has been observed. Novel fan designs with substantial noise abatement and little to no expense on aerodynamic performance have been achieved. However, the case of unfavorable installation conditions, namely fans immersed in non-ideal inlet flows, still complicates the optimization of fan designs with regard to acoustic performance. In this study, the acoustic performance alteration of a low-speed axial fan with a rotating ring is documented. Different inlet geometries are tested, while the fan aerodynamic performance is also monitored. The acoustic performance of the fan, including sound power and sound quality metrics, is discussed for three operating points. Furthermore, a parallel fan setup is tested to study the emergence of acoustic interference. Results show marginal gains in aerodynamic performance for elongated inlet geometries. On the contrary, acoustic performance and sound quality are negatively affected, particularly at high loading. Moreover, the inlet configuration with an elongated straight duct demonstrates weak coupling to loading conditions concerning sound power and roughness. An overall consistent scaling of aerodynamic and acoustic performance is observed for the parallel fan system when compared to the single fan case, irrespective of inlet geometry. Sound quality estimates of two incoherent sound sources agree well with measured values of the parallel fan system, apart from fluctuation strength, which is overestimated at stall conditions.

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.

In boilers and heat exchangers devices, tube banks are used to transfer heat. One of the commonly used arrangement in heat exchangers are staggered tube banks, which consists of tubes arranged in triangular array form. The tube banks are characterized by their longitudinal and transverse pitch ratios, which is the pitch-to- diameter ratio. Based on the pitch ratio the tube bank is considered either a compact or a widely spaced tube bank arrangement. The tube bank may cause acoustic instabilities in the system. In this study, an investigation was performed to analyse the aero-acoustic properties of tube bank samples. Experiments were conducted for three staggered tube bank samples with pitch ratio varying from 1.2 (compact arrangement) to 2 (widely spaced arrangement). Passive properties determine the sound propagation through the system, while the active acoustic properties describe the acoustic source in the system. The attention is in this paper on the passive acoustic properties of staggered tube banks. The experimental results consist of scattering coefficients for samples with different pitch ratios and power balance for all three samples which are compared to see the pitch ratio effect on the acoustic properties.

Tube banks are common design elements in heat exchangers. The most common tube bank patterns are in-line tube banks which consists of tubes spaced parallel and equally. Tube banks are characterized by their longitudinal and transverse pitch ratios (pitch to diameter). The tube bank with a pitch ratio of less than 1.25 is considered a compact tube bank and a pitch ratio equal to or greater than 2 is considered as widely spaced. In this paper, the attention is focused on the effects of pitch ratio in tube banks on its passive acoustics properties which are experimentally investigated. The flow duct experimentation is performed with flow to analyse the passive acoustic properties of tube banks. The experiment is conducted for three In-line tube banks with pitch ratios 1.2,1.4 and 2. The Experimental results consist of scattering matrix coefficients and power balance. The results are compared to see the pitch ratio effect. Transmission and reflection coefficients were found to increase with frequency for higher flow speeds and shows more waviness for compact tube bank. The power balance is calculated to see the amplification and attenuation effects of the tube bank. It is observed that compact tube banks give amplification for higher frequencies and wide spaced tube bank give moderate attenuation for all frequencies.

Vehicle electrification is one of the biggest trends in the automotive industry. Without the presence of combustion engine, which is the main noise source on conventional vehicles, noise from other components becomes more perceivable; among these components, the cooling fan is one of the major noise sources, especially during battery charging. The design of cooling fan modules is usually carried out in the early stage before building prototype vehicles. Therefore, understanding the installation effects of the cooling fan on the radiated sound is essential to secure good customer satisfaction. In this study, three different measurement setups of cooling fans are carried out: free field, wall mounted, and in-vehicle measurement. Four cooling fan prototypes with different fan blade designs are used in each measurement. Correlations of these measurements are investigated through comparisons of the measurement results. The installation effects are identified through spectrum difference between free field and in-vehicle measurement. A spectral decomposition method is implemented to enable the separation of source strength and propagation effect in the results. One variable is introduced to represent the installation effects of vehicles tested in the present study. 

Thermoacoustic engine has been proven to be a promising technology for automotive exhaust waste heat recovery to save fossil fuel and reduce emission thanks to its ability to convert heat into acoustic energy which, hence, can be harvested in useful electrical energy. In this paper, based on the practical thermodynamic parameters of the automotive exhaust gas, including mass flow rate and temperature, two traveling-wave thermoacoustic engines are designed and optimized for the typical heavy-duty and light-duty vehicles, respectively, to extract and reutilize their exhaust waste heat. Firstly, nonlinear thermoacoustic models for each component of a thermoacoustic engine are established in the frequency domain, by which any potential steady operating point of the engine is available. Then, a matching between the required heat for the engine and the available heat from the exhaust gas is performed to determine the practical operating point and the performance of the thermoacoustic engine driven by this exhaust gas with a specified thermodynamic state. Furthermore, an outline-size optimization of the thermoacoustic engines is carried out for the heavy-duty and light-duty applications, respectively, to improve the waste heat utilization efficiency and maximize the acoustic power. To consider the impact of the system weight on vehicles, a power-to-weight ratio is adopted in this work as the optimization objective. It's shown that the optimum system outside diameters for the heavy- and light-duty applications are different due to the different thermodynamic characteristics of the exhaust gas. The available acoustic powers with the maximum power-to-weight ratio for heavy- and light-duty applications are approximately 515 Watts and 935 Watts with 8.2% and 18% of thermal efficiency, respectively, corresponding to 29.3% and 42.9% of their respective Carnot efficiencies. The resulted CO2 emission reductions are approximately 0.37 kg/h and 0.77 kg/h, respectively.

Heat exchangers and boilers are widely used in various applications. High-level sound generation and thermoacoustic instability in these systems can results in serious problems such as plant shut-downs. In this study the aeroacoustic characteristics of tube bundles typically used in heat exchangers was analyzed. The tube bundles can potentially act as a passive control system for instabilities as they can be designed to change the reflection, transmission and absorption of incident sound waves. This paper presents a fundamental experimental study of the aeroacoustic characteristics of two rows of tubes in In-lined and staggered configuration, respectively. The flow duct experimentation is done with multi microphone technique with and without bias flow (through flow). The experimental results are compared with earlier results from a single tube row.