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Salt precipitation is a crucial process occurring during CO2 injection into saline aquifers. It significantly alters the porous space, leading to reduced permeability and impaired injectivity. While the dynamics of precipitation have been studied within porous media, our understanding of precipitation patterns and permeability evolution within rough fractures remains inadequate. Here, we conduct flow‐visualization experiments on salt precipitation, wherein dry air invades brine‐filled rough fractures under various flow rate conditions. Our observations reveal that the precipitation pattern shifts from ex situ precipitation to homogeneous form as the flow rate (capillary number Ca) increases. Through real‐time imaging of the salt precipitation process, we determine that ex situ precipitation is due to capillary‐driven backflow. This backflow phenomenon occurs when previously precipitated salt, acting as a hydrophilic porous medium, attracts the brine flow backward. As a result, precipitation occurs at a location different from the original site. We further show that the impact of capillary‐driven backflow is significant at low flow rates and is gradually suppressed as the flow rate increases. We provide a theoretical estimation for the critical Ca for the occurrence of capillary‐driven backflow. As Ca is smaller than this critical value, backflow‐precipitation positive feedback causes fracture voids to become completely clogged, thereby leading to a more substantial permeability reduction. In contrast, a homogeneous precipitation pattern tends to only partially clog the fracture voids, causing a relatively smaller permeability reduction. This study enhances our understanding of the role of capillary‐driven backflow in controlling salt precipitation and permeability reduction in fractures. Plain Language Summary Injecting CO2 into underground water layers (saline aquifers) is one way to tackle climate change by storing it away from the air. However, this process can lead to salt formation within the rock fractures, especially near the injection well, which can block the flow pathways and make it more challenging to inject additional CO2. Our research focuses on how salt forms within the rock fractures when we introduce dry air into areas filled with salty water, at different flow rates. We discover that at slower flow rate, the salt forms in patches due to a process where the salt already formed pulls more water toward it, leading to blockages. At higher flow rates, this doesn’t happen, and the salt is distributed more uniformly, causing less blockage. We identify a specific flow rate at which the transition between these two types of salt formation occurs. Understanding this can help us better manage CO2 injection strategies and make it more effective by minimizing the risk of blockages. This work is important for enhancing how we store CO2 underground, an important strategy in reducing its levels in the atmosphere and fighting global warming. Key Points We show that precipitation pattern shifts from ex situ to homogeneous form and ex situ precipitation is due to capillary‐driven backflow We verify that capillary‐driven backflow occurs when previously precipitated salt, as a hydrophilic porous medium, draws brine flow back We quantify that capillary‐driven backflow causes voids to be completely clogged, leading to a more substantial permeability reductions

This paper presents three-dimensional (3D) direct numerical simulations (DNS) of flow past a circular cylinder over a range of Reynolds number ( $Re$ ) up to 300. The gradual wake transition process from mode A* (i.e. mode A with large-scale vortex dislocations) to mode B is well captured over a range of $Re$ from 230 to 260. The mode swapping process is investigated in detail with the aid of numerical flow visualization. It is found that the mode B structures in the transition process are developed based on the streamwise vortices of mode A or A* which destabilize the braid shear layer region. For each case within the transition range, the transient mode swapping process consists of dislocation and non-dislocation cycles. With the increase of $Re$ , it becomes more difficult to trigger dislocations from the pure mode A structure and form a dislocation cycle, and each dislocation stage becomes shorter in duration, resulting in a continuous decrease in the probability of occurrence of mode A* and a continuous increase in the probability of occurrence of mode B. The occurrence of mode A* results in a relatively strong flow three-dimensionality. A critical condition is confirmed at approximately $Re=265{-}270$ , where the weakest flow three-dimensionality is observed, marking a transition from the disappearance of mode A* to the emergence of increasingly disordered mode B structures.

The introduction of Maritime Autonomous Surface Ships (MASS) and the accelerating digitalization of ports require precise and dynamic analysis of traffic conditions. However, conventional marine traffic analyses have been limited to low-resolution grids and static density visualizations without fully integrating vessel direction and speed. To address this limitation, this study proposes a traffic flow visualization model that incorporates dynamic maritime traffic structure. The model integrates density, dominant direction, and average speed into a single symbol, thereby complementing the limitations of static analyses. In addition, high-resolution grids of approximately 90 m were applied to enable detailed analysis. AIS data collected between 2022–2023 from the coastal waters of Mokpo, South Korea, were preprocessed, aggregated into grid cells, and analyzed to estimate representative directions (at 10° intervals) as well as average speeds. These results were visualized through color, thickness, length, and direction of arrows. The analysis showed high-density, low-speed traffic patterns and starboard-passage behavior in port approaches and narrow channels, while irregular directions with low density were observed in non-standard routes. The proposed model provides a visual representation of dynamic traffic structures that cannot be revealed by density maps alone, thus offering practical applicability for MASS route planning, VTS operation support, and risk assessment.

In this paper, we addressed the flow patterns over a light boxplane scale model to explain the previously discovered disagreement between its predicted and experimental aerodynamic characteristics. By tuft flow and CFD visualization, we explored the causes yielding a large zero lift pitching moment coefficient, lateral divergence, difference in fore and aft elevator lift, and poor high lift performance of the aircraft. The investigation revealed that the discrepancy in the pitching moment coefficient and lateral stability derivatives can be attributed to insufficient accuracy of the used predictive methods. The difference in fore and aft elevator lift and poor high lift performance of the aircraft may occur due to the low local Reynolds number, which causes the early flow separation over the elevators and flaperons when deflected downward at angles exceeding 10°. Additionally, some airframe changes are suggested to alleviate the lateral divergence of the model.

Thermographic flow visualization is a non-contact, non-invasive approach for assessing the aerodynamic state of wind turbine rotor blades and, as a result, the overall efficiency of the wind turbine. The distinguishability between the laminar and turbulent flow regimes in operating wind turbines cannot be easily increased intentionally and is totally dependent on the energy input from the sun. To deal with low-contrast measurement conditions and improve the distinguishability between flow regimes, advanced image processing using the feature extraction method principal component analysis is used. The image processing is applied to an image series of thermographic flow visualizations of a steady flow situation in a free-field experiment on a wind turbine in operation with a low distinguishability between the laminar and turbulent flow regime. The resulting feature images, based on the temporal intensity fluctuations in the images, are evaluated with regard to the global distinguishability between the laminar and turbulent flow regime. By applying the principal component analysis, the contrast-to-noise ratio was increased by a factor of 2.5. Furthermore, the resulting flow visualizations enable a localization of the laminar-turbulent flow transition, that is not possible in the raw data due to missing features in the intensity profile that allow a clear separation.

Non-uniform temperature distributions in air-conditioned areas can reduce the energy efficiency of air conditioners and cause uncomfortable thermal sensations for occupants. Furthermore, it is impractical to use physical sensors to measure the local temperature at every position. This study developed a soft-sensing model that integrates the fundamentals of thermodynamics and transport phenomena to predict the temperature at the target position in space. Water experiments were conducted to simulate indoor conditions in an air-conditioning cooling mode. The transient temperatures of various positions were measured for model training and validation. The velocity vectors of water flow were acquired using the particle image velocimetry method. Correlation analysis of various positions was conducted to select the input variable. The soft-sensing model was developed using the multiple linear regression method. The model for the top layer was modified by the correction of dead time. The experimental results showed the temperature inhomogeneity between different layers. The temperature at each target position under two initial temperatures and two flow rates was accurately predicted with a mean absolute error within 0.69 K. Moreover, the temperature under different flow rates can be predicted with one model. Therefore, this soft-sensing model has the potential to be integrated into air-conditioning systems.

Among extreme sports are wingsuits, which influence the safety and quality of an athlete’s flight through their reliability, ergonomics, and aerodynamics. Aerodynamic efficiency and wing surface reinforcement are due to ridges aligned with flow directions. Wrinkles appeared as a result of these. The created uneven surfaces have a significant effect on the performance, the arrangement and geometric shape of the surface can be useful or destructive in different flight situations. Geometric changes on the surface are one of the passive flow control methods. In this article, the geometric structure of these wavy protrusions and their effects on the flight performance of the wingsuit has been investigated. Flow structure is shown using the tuft flow visualization method, which shows the effects of geometric changes on the model in flight angles of attack (AOAs). The wingsuit model was also tested under different AOAs, and the best performance was achieved at AOA = 10 ° with seven wave ridges arranged on it. Based on the results of this study, we have evaluated the effect of the AOA, the side angle, and the Reynolds number (Re) on the performance of the model. Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 1 Given name: [Mohsen Nazemian] Last name [Alaei] and Author 2 Given name: [Mohammad Sadegh] Last name [Valipour]. Also, kindly confirm the details in the metadata are correct.It is checked and there is no problem.Please check the edit made in the article title.It is checked and there is no problem.

This study aimed to determine the optimal rotor spacing of two vertical-axis wind turbines, which are simulated by miniature models arranged side-by-side with a relatively low aspect ratio. Wind tunnel experiments with a pair of 3-D printed model rotors were conducted at a uniform velocity. A series of experiments were conducted involving both incremental adjustments to the rotor gaps, g, and the rotational direction of each rotor. Increases in the power and the related flow patterns were observed in all three arrangements: Co-Rotating (CO), Counter-Up (CU), and Counter-Down (CD). The maximum phase-synchronized rotational speed occurs at the narrowest gap in the CD arrangement. Meanwhile, local maxima arise in the CO and CU arrangements at g/D < 1, where D is the rotor diameter. From an engineering perspective, the optimal rotor spacing is g/D = 0.2 with the CO arrangement, using the same two rotors rotating in the same direction. Based on flow visualization using a smoke-wire method at a narrower gap opening of 0.2D, the wake width in the case of the CU arrangement was remarkably narrower than those obtained in the CO and CD arrangements. In the CU arrangement, a movement towards the center of the rotor pair of the nominal front-stagnation point of each rotor was confirmed via flow visualization. This finding explains a reduction tendency in the rotational speed of the rotors via a reduction in the lift in the CU arrangement.

Cavitation generation methods have been used in multifarious directions because of their diversity, and numerous studies and discussions have been conducted on cavitation generation methods. This study aims to explore the generating mechanism and evolution law of volume alternate cavitation (VAC). In the VAC, liquid water is placed in an airtight container with a variable volume. As the volume alternately changes, the liquid water inside the container continues to cavitate. Then, the mixture turbulence model and in-cylinder dynamic grid model are adopted to conduct computational fluid dynamics simulation of volume alternate cavitation. In the simulation, the cloud images at seven heights on the central axis are monitored, and the phenomenon and mechanism of height and eccentricity are analyzed in detail. By employing the cavitation flow visualization method, the generating mechanism and evolution law of cavitation are revealed. The synergistic effects of experiments and high-speed camera capturing confirm the correctness of the simulation results. In the experiment, the volume change stroke of the airtight container is set to 20 mm, the volume change frequency is 18 Hz, and the shooting frequency of the high-speed camera is set to 10000 FPS. The experimental results indicate that the position of the cavitation phenomenon has a reasonable law during the whole evolution cycle of the cavitation cloud. Also, the volume alternation cycle corresponds to the generation, development, and collapse stages of cavitation bubbles.