Investigation on the drainage condition within the ballast layer based on 3D CFD simulations

Optimization methods have been widely applied to the aerodynamic design of gas turbine blades. While applying optimization to high-fidelity computational fluid dynamics (CFD) simulations has proven capable of improving engineering design performance, a challenge has been overcoming the prolonged run-time due to the computationally expensive CFD runs. Reduced-order models and, more recently, machine learning methods have been increasingly used in gas turbine studies to predict performance metrics and operational characteristics, model turbulence, and optimize designs. The application of machine learning methods allows for utilizing existing knowledge and datasets from different sources, such as previous experiments, CFD, low-fidelity simulations, 1D or system-level studies. The present study investigates inserting a machine learning model that utilizes such data into a high-fidelity CFD driven optimization process, and hence effectively reduces the number of required evaluations of the CFD model. Artificial Neural Network (ANN) models were trained on data from over three thousand two-dimensional (2D) CFD analyses of turbine blade cross-sections. The trained ANN models were then used as surrogates in a nested optimization process alongside a full three-dimensional Navier–Stokes CFD simulation. The much lower evaluation cost of the ANN model allows for tens of thousands of design evaluations to guide the search of the best blade profiles to be used in the more expensive, high-fidelity CFD runs, improving the progress of the optimization while reducing the required computation time. It is estimated that the current workflow achieves a five-fold reduction in computational time in comparison to an optimization process that is based on three-dimensional (3D) CFD simulations alone. The methodology is demonstrated on the NASA/General Electric Energy Efficient Engine (E3) high pressure turbine blade and found Pareto front designs with improved blade efficiency and power over the baseline. Quantitative analysis of the optimization data reveals that some design parameters in the present study are more influential than others, such as the lean angle and tip scaling factor. Examining the optimized designs also provides insight into the physics, showing that the optimized designs have a lower amount of pressure drop near the trailing edge, but have an earlier onset of pressure drop on the suction side surface when compared to the baseline design, contributing to the observed improvements in efficiency and power.

The article is directly related to the authors’ previous study of the remotely operated underwater vehicle’s (ROV) motion, where the mathematical model of the ROV motion is derived for laminar flow of water. This solution of the ROV motion has been improved by using the three-dimensional computational fluid dynamics (CFD) simulation that allows simulating the turbulent flow, which is mainly generated by propellers. Both methods were coupled to obtain more accurate values of hydrodynamic damping coefficients for the improved determination of the ROV motion velocity. Results of the solution are discussed and some of them are compared with the experiment.

One of the major barriers for polymer electrolyte membrane (PEM) fuel cells to be commercially viable for stationary and transport applications is the durability of membranes undergoing chemical and mechanical degradation over the period of operation. Toward understanding the effects of operating parameters on membrane durability, this paper presents numerical simulations for a single channel PEM fuel cell undergoing changes in load, by subjecting the unit cell to step change in voltage. The objective is to elucidate the mechanical response of membrane, which is subjected to hygral (water) loading and unloading cycles at constant temperature. Detailed three-dimensional (3D) computational fluid dynamics (CFD) simulations are conducted, taking in to account the complex interactions of water transport dynamics and load changes, to accurately capture the water content in the membrane with changes in cell voltage. The water content obtained through CFD simulations is, in turn, used to carry out two-dimensional (2D) finite element (FE) analysis to predict the mechanical response of the membrane undergoing cyclic change in water content, as the operating voltage is cycled. The effects of cyclic changes in cell potential on the stresses induced, amount of plastic strain and their localization are analyzed for various inlet cathode humidity values for two sections along the length of the fuel cell.

Rationale: We previously found oropharyngeal enlargement and subglottal narrowing in asthma and chronic obstructive pulmonary disease (COPD) patients compared to healthy individuals. This study aimed to investigate the impact of oropharyngeal remodeling on the upper airway airflow dynamics in association with lung structure-function impairment in obstructive lung disease (OLD). Methods: Upper airway computed tomography (CT) scans, inspiratory (total lung capacity) and expiratory (functional residual capacity) lung CTs, and clinical data were collected from 185 participants (26 healthy, 56.6±5.1y; 73 COPD, 71.1±7.5y, and 86 asthma, 64.8±12.5y) enrolled in Jeonbuk National University Hospital, Jeonju, Korea. We conducted quantitative inspiratory-expiratory CT analysis and one-dimensional (1D) computational fluid dynamics (CFD) simulations of airflow in the lower airways, for all participants. Then, we selected ten representative subjects in each group based on key features of upper airways (healthy: 56±6.2y; COPD: 69.7±7.4y; asthma: 63.2±6.3y) and conducted three-dimensional (3D) CFD simulations of breathing (tidal volume: 6 ml/kg). Results: Patients with OLD showed 11 times greater CFD-derived lower airway resistance and 3.8% smaller transpulmonary pressure than healthy controls. 3D CFD simulations showed less pressure drop from the mouth to the level of the sixth cervical vertebra (C6) during inhalation in OLD (COPD: 37.3±41.9Pa; asthma: 32.01±18.4 Pa) than in healthy subjects (70.7±48.5) Pa. Upper (oropharyngeal) airway resistance was also smaller in OLD (COPD: 155.0±188.0 kPa·s/m³; asthma: 116.2±61.5 kPa·s/m³) than in healthy subjects (229.4±142.2 kPa·s/m³). This is attributable to oropharyngeal enlargement measured by greater oral space air fraction and larger supraglottal airway diameter at the level of the fourth cervical vertebra (C4). Less upper airway pressure drop to the level of C6 correlated with upper airway enlargement measured by normalized upper airway air volume (r=-0.60, p<0.001) and diameter at C4 (r=-0.56, p=0.001) as well as lung structure-function impairment such as functional small airways disease percent (fSAD%), less volumetric deformation (J), and less relative displacement (s[asterisk]) (r=-0.40, 0.47, 0.54; p=0.030, 0.009, 0.002) and worse spirometry outcomes such as post-BD FEV1% (r=0.54, p=0.002) and FEV1/FVC (r=0.54, p=0.002). Conclusion: CT-based CFD simulations showed patients with obstructive lung disease experienced elevated airway resistance in the lower airways but reduced pressure drop and airway resistance due to oropharyngeal enlargement during inhalation. Reduced aerodynamic effort may help compensate excessive respiratory effort required in the lower airways. Findings suggest that upper airway imaging and airflow analysis allows more complete interpretation of the entire respiratory function altered with airflow obstruction.

CFD simulation and experimental validation of a GM type double inlet pulse tube refrigerator

Effect of geometry on the thermal behavior of catalytic micro-combustors

Investigating the impact of gas emission uncertainty on airflow distribution in an auxiliary ventilation system using CFD and Monte-Carlo simulation

CFD simulations of the wind environment around an airport terminal building

In industrial environments, boiler units are widely used to supply heat and electrical power. At an integrated steel mill, industrial boilers combust a variable mixture of metallurgical gases combined with additional fuels to generate high-pressure superheated steam. Most tangentially fired boilers have experienced water wall tube failures in the combustion zone, which are thought to be caused by some deficiency in the combustion process. The challenge faced in this present process is that there are very limited means to observe the boiler operation. In this study, a three-dimensional Computational Fluid Dynamics (CFD) modeling and simulation of an industrial tangentially fired boiler firing metallurgical gases was conducted. Simulation results obtained from the assembled CFD model were validated by industrial experiments. A quick comparison of the flame shape from the simulation to the actual flame in the boiler showed a good agreement. The flow field and temperature distribution inside the tangentially fired boiler were analyzed under the operation conditions, and a wall water tube overheating problem was observed and directly related to the flow characteristics.

As part of the Hypersonic International Flight Research Experimentation (HIFiRE) Direct-Connect Rig (HDCR) test and analysis activity, three-dimensional computational fluid dynamics (CFD) simulations were performed using two Reynolds-Averaged Navier Stokes solvers. Measurements obtained from ground testing in the NASA Langley Arc-Heated Scramjet Test Facility (AHSTF) were used to specify inflow conditions for the simulations and combustor data from four representative tests were used as benchmarks. Test cases at simulated flight enthalpies of Mach 5.84, 6.5, 7.5, and 8.0 were analyzed. Modeling parameters (e.g., turbulent Schmidt number and compressibility treatment) were tuned such that the CFD results closely matched the experimental results. The tuned modeling parameters were used to establish a standard practice in HIFiRE combustor analysis. Combustor performance and operating mode were examined and were found to meet or exceed the objectives of the HIFiRE Flight 2 experiment. In addition, the calibrated CFD tools were then applied to make predictions of combustor operation and performance for the flight configuration and to aid in understanding the impacts of ground and flight uncertainties on combustor operation.

Patients with chronic kidney disease suffer from immune dysfunction, increasing susceptibility to infections. The aim of the study was to investigate air contamination with respiratory viruses in a dialysis unit at a quaternary hospital using molecular detection techniques and to analyze airflow dynamics through computational fluid dynamics (CFD) simulations for a comprehensive assessment of air transmission risks. We conducted dialysis unit air sampling using AerosolSense™ samplers. Air and clinical sampling occurred during three periods in 2022: winter, early, and late fall. A technical team maintained the dialysis unit's ventilation system during mid fall. Ventilation system capacity and airflow rates were measured. CFD simulations were used to evaluate airflow dynamics. The investigation collected 144 air samples, revealing heterogeneous virus detection rates across locations and study periods. Virus positivity correlated with the presence of patients and the effectiveness of the ventilation system. The ratio of virus air positivity to virus patient positivity was 1.84 and 3.35 during the first and the second periods, respectively, and collapsed to 0.64 after maintenance. Airflow rate measurements highlighted a ninefold discrepancy between actual and theoretical airflow (393 m3/h vs. 3530 m3/h), which was rectified by maintenance actions. Airflow dynamics and particle dispersion visualization through CFD simulations contributed to a better understanding of transmission risks. Detection of viruses in the air, combined with CFD, revealed deficiencies in air renewal. Maintenance interventions significantly improved airflow dynamics and particle dispersion, reducing airborne virus spread.

Microchannels can create disturbed flow patterns by altering pressure gradients, shear forces, and flow symmetry, which are essential in the design of microfluidic devices and, hence, blood-contacting devices. The effect of asymmetric stenosis on pressure, wall shear stress, and velocity in rectangular and circular microchannels with same operating conditions was analyzed in this study using three-dimensional (3D) steady laminar computational fluid dynamics (CFD) simulations. Asymmetric flow patterns induced by asymmetric stenosis are of particular importance and remain underexplored, especially in the context of multiple constrictions. This is, to our knowledge, is the first systematic CFD comparison of multiple asymmetric stenoses in circular microchannels directly contrasted with rectangular and single-stenosis cases under identical settings. Several parameters, such as wall shear stress (WSS), pressure, and velocity distributions, were analyzed in various stenotic and non-stenotic geometries. These microchannel models, while not reflecting real blood vessels themselves nor exhibiting wall compliance, pulsatility, or non-Newtonian rheology, replicate important mechanical characteristics of stenosis-mediated flow disturbance. Single and multiple asymmetric stenoses create flow patterns that are similar to those of vascular pathologies. For this reason, these channels should be considered as simplified device-scale models of vascular phenomena as opposed to realistic, in vitro vascular models. The results showed that asymmetric stenosis creates asymmetric velocity peaks and elevated WSS, which are more evident in the case of circular configurations with double asymmetric stenosis. The findings will help design microfluidic devices that mimic unstable flow characteristics that occur in stenotic conditions, and assist in testing clinical devices. In this study, two fabrication-ready microchannel designs under fixed operating conditions (identical inlet velocity and fluid properties) that reflect common microfluidic use were compared. Consequently, all pressure, velocity, and WSS outcomes are interpreted as device-scale responses under fixed velocity, rather than a fundamental isolation of cross-section shape, which would require matched hydraulic diameters or flow rates. This study is explicitly device-oriented, representing a fixed operating point rather than a strict geometric isolation. Accordingly, the results are also expressed with dimensionless loss coefficients (Ktot and Klocal) to enable scale-independent, device-level comparison.

Horizontal gravity separators are important components in the production of unconventional petroleum resources. While tremendous efforts have made on the sizing of separators, relatively few studies have addressed their operational performance under varying outlet conditions. This study aims to investigate the effect of water outlet pressure on the performance of the separator to establish guidelines for its proper operation. Three-dimensional computational fluid dynamics (CFD) simulations are conducted using the Eulerian multiphase model and interfacial concentration area. Four water outlet pressures ranging from 7537.2 to 7421.9 Pa are examined under fixed inlet flow rates. The numerical method is validated by comparing it with experimental results. The numerical results confirm that the separation efficiency improves as the water outlet pressure decreases primarily due to the increased thickness of the oil pad. Notably, the analysis reveals that meeting residence time criteria alone does not guarantee high separation performance, as outlet pressure significantly affects fluid distribution and phase separation. These findings suggest that maintaining the water outlet pressure below 7448.5 Pa is essential for achieving efficient separation in practical operations.

High pressure ratio, radial-inflow turbines typically experience supersonic expansion in the nozzle section. Accurate estimation of the flow conditions and velocity triangle at the nozzle outlet is of critical importance in correctly predicting the overall turbine performance. The meanline modeling of such a nozzle requires special attention, due to the significantly altered flow field downstream of the throat. In this study, the flow field of a supersonic expansion nozzle is investigated, using a three-dimensional (3D) computational fluid dynamics (CFD) simulation calibrated with test data. Three different CFD configurations are explored: the nozzle alone, the nozzle plus rotor coupled with a mixing plane, and the nozzle plus rotor coupled with the nonlinear harmonic (NLH) method. These configurations are compared to each other to gauge the effect of the rotor and stator interaction and the potential for error in establishing the velocity triangles. The exit vane angle, number of vanes, and expansion ratio across the nozzle are systematically varied to provide the data as the base for nozzle modeling. Finally, a meanline method is proposed to calculate the pressure loss and flow deviation at the nozzle outlet and is compared with CFD results.

While designing the power requirements of a ship, the most important factor to be considered is the ship resistance, or the sea drag forces acting on the ship. It is important to have an estimate of the ship resistance while designing the propulsion system since the power required to overcome the sea drag forces contribute to ‘losses’ in the propulsion system. There are three main methods to calculate ship resistance: Statistical methods like the Holtrop-Mennen (HM) method, numerical analysis or CFD (Computational Fluid Dynamics) simulations, and model testing, i.e. scaled model tests in towing tanks. At the start of the design stage, when only basic ship parameters are available, only statistical models like the HM method can be used. Numerical analysis/ CFD simulations and model tests can be performed only when the complete 3D design of the ship is completed. The present paper aims at predicting the calm water ship resistance using CFD simulations, using the Flow-3D software package. A case study of a roll-on/roll-off passenger (RoPax) ferry was investigated. Ship resistance was calculated at various ship speeds. Since the mesh affects the results in any CFD simulation, multiple meshes were used to check the mesh sensitivity. The results from the simulations were compared with the estimate from the HM method. The results from simulations agreed well with the HM method for low ship speeds. The difference in the results was considerably high compared to the HM method for higher ship speeds. The capability of Flow-3D to perform ship resistance analysis was demonstrated.