The viscoelastic behavior of thermoplastic polymers is significantly influenced by external conditions such as temperature and moisture. High temperatures accelerate polymer chain mobility, reducing stiffness, while moisture absorption acts as a plasticizer, altering key thermomechanical properties, including the glass transition temperature. The time- and temperature dependence for thermorheologically simple materials is effectively described by the time-temperature superposition principle. This study aims to describe the material properties of the thermoplastic polymers continuously under varying temperatures and moisture levels within the glass transition range. Fractional models are attractive for describing moisture-dependent material properties due to the few required parameters. Furthermore, in contrast to standard discrete rheological models, fractional approaches can accurately capture the distinct asymptotic behavior of the loss factor of the thermoplastic polymers. We validate the performance of a fractional model using a new data set that incrementally resolves the influence of moisture on mechanical properties and evaluate it against the well-established generalized Maxwell model. The results demonstrate that the fractional model accurately predicts the moisture-dependent thermoviscoelastic material behavior and requires significantly fewer model parameters compared to standard discrete rheological models.

Advanced fuel injection systems are vital for improving combustion performance and reducing emissions in liquid-fuel-powered, high-momentum jet-stabilised combustion systems. This paper introduces an additively manufactured (AM) μ-scale annular slit injector with a nominal gap width of 50μm, realised by laser powder bed fusion in Inconel 718. μ-XRCT measurements confirm a manufacturable width of 52μm and reveal a transition towards statistically isotropic circumferential discharge at the slit exit. Compared with conventional dual airblast injection (AB), the μ-slit topology generates more uniformly fine droplets (d32 ≈ 10μm) and a markedly reduced radial asymmetry in fuel placement. The homogenised annular fuel discharge suppresses sectional bias and intermittency at the nozzle edge while enhancing fuel–air mixing, redistributing clustering length scales, and promoting more robust combustion across variations in jet velocity and fuel loading. Structural variants, e.g., μ-bumps and a low-swirler configuration, further modulate near-field multi-phase interaction and flame anchoring while enhancing overall flame homogeneity. This mixing-optimised stabilisation enhances the symmetry of the OH∗-marked heat-release structures and enables stable low-NOX combustion under lean atmospheric conditions. The injector operates with a comparatively low pressure drop with excellent reproducibility across all investigated mass flow rates, facilitating a wide dynamic operating range, yet heat transfer within the μ-channels under elevated preheating conditions requires further investigation. These results establish the AM μ-slit injector as a scalable low-emission architecture for compact, jet-stabilised micro gas turbine and hybrid aero-engine combustors.

Abstract High-Performance Concrete (HPC) is gaining attention due to its exceptional compressive strength and durability. Understanding its mechanical behaviour under high-cycle fatigue loading is crucial for designing long-lasting structures. This study examines how factors like loading frequency, moisture content, and temperature affect the fatigue damage behaviour of HPC and Ultra-High-Performance Concrete (UHPC). Mechanical fatigue damage tests were conducted at different cyclic loading frequencies and upper stress levels to characterise strain evolution and its correlation with failure cycles. An evaluation method was developed to minimize variability in the relationship between failure cycles and applied load or temperature variations. High-frequency fatigue testing (20–200 Hz) simulated dynamic cyclic loading conditions. By stopping fatigue tests before complete failure, concrete samples were collected at specific damage phases and analysed using micro X-ray computed tomography (µXRCT) and dynamic mechanical analysis (DMA). This µXRCT-DMA characterization provides insights into local damage processes and the evolution of mechanical properties. Results highlight that moisture significantly impacts failure cycles, strain development, and temperature changes. The DMA and µXRCT effectively characterise stiffness degradation, while high-frequency fatigue testing enhances understanding of concrete behaviour under different frequency loads.

This study investigates the influence of network geometry, wettability, and flow conditions on end effects during steady-state immiscible two-phase flow in model pore networks. Systematic co-injection experiments were performed in planar microfluidic networks with periodic and non-periodic geometries and varying wettability characteristics, enabling direct comparison over a broad range of flow conditions, expressed in terms of capillary number and flow-rate ratio. Using the DeProF theoretical framework, pressure-drop measurements were analyzed to evaluate the flow-rate-dependency of relative permeabilities, intrinsic dynamic capillary pressure, and energy efficiency. In parallel, sub-pore-scale imaging provided direct insight into the spatiotemporal evolution of interstitial flow structures under both steady and transient flow conditions. The study: (a) further validates the DeProF framework as a robust and efficient approach for analyzing two-phase flow in porous media, capturing flow-rate dependency and energy efficiency across diverse flow conditions, fluid pairs, and pore-network configurations; and (b) demonstrates its potential to infer interstitial flow-structure characteristics from ex-core (macroscopic) relative permeability measurements. The results show that system-specific correlations can be established between macroscopic flow measurements at critical flow conditions and the underlying interstitial flow structures. These findings support the development of flow-dependent relative permeability scaling models and improved special core analysis (SCAL) protocols that more accurately capture the physics governing two-phase flow in natural porous media.

Accurate and precise contact angle measurements are critical for characterizing surface wettability and fluid–solid interfacial phenomena in scientific and engineering applications. However, most high-pressure, high-temperature (HPHT) contact angle instruments are limited to static measurements, while dynamic techniques such as tilted-plate analysis with controlled rotation remain restricted to ambient-pressure conditions. This work presents an integrated measurement system enabling both static and dynamic contact angle measurements using sessile-drop, captive-bubble, and tilted-plate techniques with continuous rotation under controlled pressure and temperature. The system integrates a titanium measurement cell designed for operation up to 50 MPa with a heating system capable of reaching 300 °C. It is coupled with a MATLAB-based image analysis framework that ensures consistent contour extraction, contactpoint detection, and contact angle computation across all techniques, thereby enabling direct comparison between techniques, reducing operator-dependent variability, and improving reproducibility. Algorithmic performance was tested using 1,600 synthetic droplet contours spanning contact angles from 5° to 173°. Bland–Altman analysis demonstrated strong agreement between the computed contact angles and the known ground-truth values. Measurement precision and system robustness were assessed using 3D-printed reference substrates containing embedded droplets with predefined geometries. An uncertainty analysis performed in accordance with the Guide to the expression of Uncertainty in Measurement (GUM) yielded an expanded uncertainty of U = 4.00° at approximately 95% confidence. Experimental demonstrations using a water–N2 system on a quartz surface at pressures up to 10 MPa and temperatures up to 110 °C confirmed stable and repeatable performance across all techniques. The proposed system provides a unified and validated platform for HPHT static and dynamic wettability characterization, achieving measurement precision comparable to commercial instruments and uniquely extending experimental capabilities through continuous-rotation tilted plate measurements under controlled pressure and temperature conditions.

Solid grains immersed in a carrier fluid can be found in many fields of engineering and geophysics. Considering single grains and especially spheroids immersed in a fluid under shear flow conditions, the rotational motion of these grains leads to the so-called Jeffery orbits. Considering both a Newtonian and non-Newtonian (Bingham–Papanastasiou) fluid, the flow behavior in the near field of such a spheroid can be analyzed in terms of hydromechanical forces between the fluid and the solid phase only numerically. Therefore, a meshless Smoothed Particle Hydrodynamics (SPH) approach is implemented to perform direct numerical simulations of a single spheroid in a Newtonian or non-Newtonian carrier fluid with and without an additional volumetric force. We study near field properties in the immediate vicinity of a solid grain rotating in shear flow (“Jeffery orbits”-like) to provide insights into the hydrodynamic interactions for a Newtonian and non-Newtonian carrier fluid by using the advantages of an SPH model that can capture this in the best way. Furthermore, we discuss and analyze parameters such as the effective viscosity of the fluid, which leads to quasi-rigid behavior in the vicinity of the solid grain. Therefore, the effective size of the solid grain appears to be larger than it naturally is. With our study, we aim to give an insight into particle–fluid interactions as well as to analyze the near field of solid spheroids immersed in a non-Newtonian fluid, as it is also done in micro-rheology studies, to form a basis for the modeling of multi-particle systems.

The mechanisms of drainage of supraglacial lakes are not yet fully understood. Here we present an indepth study of drainage characteristics of a 21km^2 large supraglacial lake in Northeast Greenland from its genesis in mid 1990s to 2023. We discuss the fracture modes involved in drainage and compare this to simulated principal stress fields. A particular focus of the presentation is the formation of gullies. Using high resolution optical satellite imagery (WV2 and Planet), we detect fracture networks at the surface. We find evidence for reactivation of former gullies in subsequent lake drainage events. In addition we present viscoelastic modelling of gullies at the surface that support the continued existence of open gullies at the surface. In vertical direction, we surveyed the glacier using airborne radio echo sounding in 2016, 2018 and 2021. This data reveals englacial channels and their remnants over the entire live span of the lake.

Kinetic interface-sensitive (KIS) tracing is a recently developed methodology to monitor the change in fluid-fluid interfacial area (FIFA) in the context of geological storage of supercritical CO2 in saline aquifers. Previous studies have demonstrated the applicability of KIS tracers at the scCO2 injection stage, while its application at the storage stage when the tracked scCO2 is residually trapped has not yet been studied. The main challenges that impede tracer application at the storage stage are the unknown concentration of the reacted tracer accumulated in the measurement region, resulting from the persistent interfacial reaction that occurs at the scCO2 / brine interface with the KIS tracer injected by the scCO2, as well as the effects of the spatial distribution and shape of residual scCO2 blobs. A "water push-pull" method is proposed here, enabling the application of the KIS tracer at the storage stage. This study applies pore-scale and field-scale numerical simulations to study the KIS tracer reactive transport during the "water push-pull" experiments. It is found that the measurement is not affected by the residual scCO2 architecture, when the Peclet number is smaller than 5. The measurement relies on the steadystate concentration distribution formed in the measurement region, resulting from the equilibrium between the reaction production and the tracer removal due to the freshwater injection. The tracer breakthrough curves (BTCs) are not affected by the initial concentration nor a change in flow rate, and correlation functions between the FIFA and the slope of the BTCs are found.

Porous materials are ubiquitous in various engineering and geological applications, where their permeability plays a critical role in viscous fluid flow and transport phenomena. Understanding and characterizing the microscale properties, the effective hydraulic parameters, and also the anisotropy of porous materials are essential for accurate modeling and predicting fluid flow behavior. The study pursues the Digital Rock Physics approach to retrieve intrinsic permeability and its evolution in anisotropic configurations of porous media, which are subjected to pore space alterations. Therefore, we discuss the development and implementation of a computational framework based on the finite difference method to solve the pseudo-unsteady Stokes equations for fluid flow on the pore scale. We present an efficient and highly parallelized implementation of this numerical method for large voxel-based data sets originating from different image-based experimental setups. A comprehensive variety of benchmarks has been conducted to assess and evaluate the performance of the proposed solver. The solver's compatibility with huge domain sizes generated by state-of-the-art imaging techniques is demonstrated. We investigate an open-cell foam undergoing deformation, observing that contrary to initial expectations, no anisotropy emerges. Further, we examine a microfluidic cell experiencing precipitation within its pore space, resulting in clear anisotropic development during the clogging process.

The viscoelastic complex Poisson’s ratio, which describes the frequency-dependent ratio of transverse and longitudinal strains, can be determined directly from simultaneous strain measurements or indirectly from successively measured complex moduli based on the elastic-viscoelastic correspondence principle (EVCP). There has been considerable debate regarding its definition and measurability, with common but often incorrect analogies to complex moduli and compliances. We investigated cylindrical samples of polymethyl methacrylate (PMMA) and Berea sandstone using different measurement set-ups to compare the two methods. For direct measurement, we used strain gauges in harmonic uniaxial tension and compression tests to measure longitudinal and transversal strains. For the indirect method, we measured the complex Young’s and shear moduli by complementing uniaxial tests with torsion experiments on the same specimen under the same conditions using a torsional-axial rheometer. Our analysis on samples from a single product line showed that both methods yielded consistent values for the absolute value of the complex Poisson’s ratio. However, the direct method provided a more accurate determination of its loss factor. Experimental results confirmed that the loss factor of the complex Poisson’s ratio can be positive or negative, depending on which strain lags more behind the axial force excitation, aligning with theoretical expectations.

This work assesses classical density functional theory (DFT) for predicting static contact angles of pure substances and mixtures by comparison with new experimental data. A Helmholtz energy functional based on perturbed-chain statistical associating fluid theory (PC-SAFT) describes fluid-fluid interactions, combined with an effective external potential for solid-fluid interactions. The solid is characterized by adjusting a single solid-solid interaction parameter to the contact angle of n-octane; all other results are predictions. Surface tensions between solid, liquid, and vapor phases are determined from one-dimensional DFT, and Young's equation yields the contact angle. Experiments employ the sessile droplet method on a nonpolar polytetrafluoroethylene (Teflon) substrate. Accurate results are achieved for pure substances except monohydric alcohols, where neglecting orientational effects contributes to systematic overestimation. For mixtures, predictions are reliable whenever the respective pure substances are described well, including polar and hydrogen-bonding systems. Overall, DFT based on PC-SAFT enables fast and accurate contact angle predictions.

This data set contains two micro X-ray Computed Tomography (micro-XRCT) data sets resulting from region of interest scans (diameter 58.32 mm, height 46.06 mm) of the center region of a stone mastic asphalt (SMA) drill core. The drill core was scanned with identical scanner settings before ("reconstructed_20200429_01.tar.gz") and after ("reconstructed_20201015_01.tar.gz") a uniaxial compression test.The sample had a diameter of 75.12 mm and a height of 70.93 mm before, respectively a diameter of 78.05 mm and a height of 67.11 mm after the compression test (measured by caliper). The asphalt mixture is a stone mastic asphalt with a nominal maximum aggregate size (NMAS) of 11 mm (SMA 11 S). It contains diabase aggregates and a 50/70 bitumen binder. The material is described in detail by Hu et al. (2017).The compression test was performed by controlling the load with the following procedure: Starting the measurement at a contact load of 10 N. Increasing the load to 500 N (stress around 0.11 N/mm2) with a speed of 100 mm/min. Holding the load at 500 N (stress around 0.11 N/mm2) for 600 s. Increasing the load by another 500 N (stress around 0.11 N/mm2) with a speed of 100 mm/min and holding it for 600 s. Repeating the procedure of adding load in 500 N (stress around 0.11 N/mm2) increments, until the maximum load of 5000 N (stress around 1.13 N/mm2) is reached and held for 600 s.During the test, time (s), distance (mm), and load (N) were logged at regular intervals and can be found in "2_1_compression_test_data.csv". A visualization of the test procedure is shown in "test_procedure.pdf".NOTE: It turned out that the specimen top and bottom surfaces were not exactly plane-parallel which led to an non-uniform transmission of the load, which lead to a first full-surface contact between the load plate and top surface of the specimen when the 1500 N load increment was reached.

The Theory of Porous Media (TPM) with an embedded phase-field approach to fracture provides an elegant opportunity to study complex flow phenomena in fractured porous materials in a unified single-domain approach. On this basis, the interactive flow behaviour between free flow and porous-media flow is studied using the example of flow through a thin porous plate containing a rectangular channel. By considering different boundary conditions and investigating the flow behaviour for a range of hydraulic conductivities, our study is designed to reveal insights into phenomena which are relevant for various sub-surface geo-engineered applications. Furthermore, we show that the applied macroscopic single-domain approach is able to reveal local flow effects near the porous interface (channel walls), namely the so-called velocity profile inversion phenomenon. Moreover, we introduce a geometrically motivated estimation of the length-scale parameter ϵ used in phase-field approaches, which is directly related to the roughness of the fracture surface. Thus, values for ϵ are proposed for microfluidic devices and different rock types. Furthermore, we apply fully three-dimensional simulations to evaluate the influence of the thickness of thin porous plates on the overall flow resistance, which is typically relevant in microfluidic devices. In a combined numerical–experimental study, we compare results from representative microfluidic experiments and simulations and confirmed the choice of ϵ to correctly predict the flow transition across the porous interface.

Alterations in the pore morphology of porous materials cause changes to the characteristic hydraulic properties, which are mostly non-linear and inherently difficult to predetermine. Assuming the alterations are known with sufficient accuracy, the relation between the altered pore structure, measured in terms of porosity, and intrinsic permeability may be determined by simulations with enormous computational effort. We focus on microfluidic experiments during the course of which the pore space becomes increasingly occupied with solid precipitate over elapsed process time. To analyze these domains, we present a novel geometry-informed drag formulation which allows for solving pseudo-3D Stokes equations for image-based input data of clogging porous media with accuracy and efficiency. In a pre-processing step, local pore space properties are analyzed and employed to spatially vary the magnitude of the drag term, which reflects the influence of neglected 3D effects. Calibration and validation is achieved through fully 3D Finite Difference Stokes simulations of different benchmark cases. With the proposed formulation we achieve the high accuracy of the pseudo-3D methods as far as permeability is concerned (<30% deviation), but also with respect to local velocities, for a microfluidic domain throughout the clogging process. Noteworthy, the computational cost is being reduced to less than 1%. Combining the efficiency of a Stokes 2D simulation and accuracy of a 3D model the presented approach is rendered an interesting option to investigate remaining open questions, for example on anisotropy of effective hydraulic parameters during the clogging process.

Including specific interfacial area and saturation of the percolating phase into two-phase porous media flow models, on the Darcy scale, enhances our ability to capture the physical properties of porous media flow more effectively. Using optical microscopy and microfluidic devices, we perform sequential drainage and imbibition experiments. The relevant processes, images, and boundary pressures are monitored, recorded, and logged at all times. For comparative purposes, two PDMS micromodels are used, one with an ortho-canonical, homogeneous, and the other with a periodic heterogeneous pore network, with similar macro- but different pore-scale properties. After processing the images, parameters like interfacial area belonging to percolating and non-percolating phases and the corresponding phase saturations are determined. Our experimental results show that the relation between specific interfacial area and saturation of the percolating invading phase is a linear relationship with interesting properties. Additionally, after a number of fluid displacement processes (drainage and imbibition), and for both pore networks, unique flow paths for both phases are formed. We speculate that this happens due to the establishment of an effective porous medium, meaning a hydro-dynamically active region within the pore space where the corresponding phase remains connected and flowing, where the capillary forces act as the guide for creating the "path of least resistance" in a highly viscous flow regime by keeping the non-percolating phases in place. As the results can be specific to our experiments, more work needs to be done toward the potential generalization of these findings, especially in 3D flow domains.

Under in-situ conditions, natural hydraulic fractures (NHF) can occur in permeable rock structures as a result of a rapid decrease of pore water accompanied by a local pressure regression. Obviously, these phenomena are of great interest for the geo-engineering community, as for instance in the framework of mining technologies. Compared to induced hydraulic fractures, NHF do not evolve under an increasing pore pressure resulting from pressing a fracking fluid in the underground but occur and evolve under local pore-pressure reductions resulting in tensile stresses in the rock material. The present contribution concerns the question under what quantitative circumstances NHF emerge and evolve. By this means, the novelty of this article results from the combination of numerical investigations based on the Theory of Porous Media with a tailored experimental protocol applied to saturated porous sandstone cylinders. The numerical investigations include both pre-existing and evolving fractures described by use of an embedded phase-field fracture model. Based on this procedure, representative mechanical and hydraulic loading scenarios are simulated that are in line with experimental investigations on low-permeable sandstone cylinders accomplished in the Porous Media Lab of the University of Stuttgart. The values of two parameters, the hydraulic conductivity of the sandstone and the critical energy release rate of the fracture model, have turned out essential for the occurrence of tensile fractures in the sandstone cores, where the latter is quantitatively estimated by a comparison of experimental and numerical results. This parameter can be taken as reference for further studies of in-situ NHF phenomena and experimental results.

This study investigates the capillary-associated interfacial area during primary drainage in unconsolidated porous media for different mean grain diameters, employing pore-scale numerical simulation with the phase-field method. Five, two-dimensional porous media are generated with the same grain/pore size uniformity, but different mean grain diameters, ranging between 0.24 mm and 0.94 mm. Three cases are considered, representing stable displacement, crossover zone and viscous-fingering regimes. The findings reveal that the capillary-associated interfacial production rate increases with decreasing grain size. Specifically, the capillary-associated interfacial production rate is higher for the viscous-fingering regime compared to the stable displacement. The maximum capillary-associated interfacial area obtained for different grain sizes agrees with the correlation established in our previous study using the kinetic interface-sensitive tracer. Furthermore, the capillary-associated interfacial area is divided into two parts: one related to the disconnected water clusters and the other related to the connected water. The disconnected capillary-associated interfacial area correlates with the average volume of the clusters, following an exponential function. Furthermore, the average volume of the clusters depends on both, the grain size and displacement regime. Moreover, it is found that the displacement regime has a great impact on the connected capillary-associated interfacial area. For stable displacement, the connected capillary-associated interfacial area is larger for larger mean grain diameter. In contrast, for fingering, the connected capillary-associated interfacial area is smaller for increasing mean grain diameter.

Permeable, media transporting, components are an integral part in numerous technical applications. In gas turbines combustors, for example, gaseous oxidizer and fuel are transported separately into the burner, where they are injected and mixed, and subsequently combusted. The mixture homogeneity strongly affects the combustion performance and emissions formation and is, amongst other, determined by the spatial distribution of fuel injection ports. In this context, porous media provide the limiting case for a spatial distribution of mediainjecting pores, yet is typically associated with a high pressure drop that yields a loss in efficiency. In this study, possibilities of achieving gas permeability in additively manufactured porous structures are investigated. The objective is to selectively functionalize the permeable layers for gaseous media supply with low pressure loss and, when needed, enable a targeted mixing of different gas streams. For this purpose, a laser-based powder bed fusion process (PBF-LB/M) was used in this study. It offers the opportunity to manufacture varying porosities inside complex monolithic metal parts. To produce the porous structures and to achieve gas permeability, the effect of scan rotation angle, hatch distance, build-up direction and length of the porous specimen is investigated. Due to the high temperatures present in combustion systems, the present work utilizes Inconel 718 material. The AM gas permeable specimen are experimentally characterized by means of surface topography, micro X-ray computed tomography (mu XRCT) as well as flow and pressure loss test. The results show, that the AM process parameter provide effective control parameters to adjust the permeability. The strongest effect originates from the hatch distance for a given build-up direction. Depending on the scan rotation, the flow transitions from a turbulent pipe flow to a Darcy flow as present in conventional porous media. A structured alignment and connectivity of pores can be realized as evident in the mu XRCT results, surface topography and the flow measurements. Residual powder, powder adhering to the pore walls and stochastic closure of pores or channels lead to deviations and need to be considered when designing respective parts. Nonetheless, the results further show that a directional dependence of the permeability and the build-up direction can be realized and controlled. Consequently, when considering the AM build-strategy in the design of components, this directed permeability can be functionalized in the generation of gas transporting and gas mixing layers separately by adjusting the AM processing parameter.