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Reynolds-averaged Navier–Stokes simulations are performed for supersonic turbulent flow over a cylinder/flare with upstream surface distortion representative of structural deformation induced via fluid–structural and fluid–thermal–structural behavior. Broad parametric analysis is carried out through the generation of Kriging-response surfaces from a database of general simulations. A posteriori simulations are then carried out at parametric combinations that correspond to extrema in the Kriging response surfaces to gain deeper insights into the interaction between the surface distortion and flow responses. Upstream distortions tend to decrease, rather than increase, the peak pressure and heat flux loads on the flare compared to an undeformed cylinder. Furthermore, decreases in these quantities reach up to O(10%) compared to up to O(1%) for increases. Integrated quantities over the flare are relatively insensitive to upstream distortion. The corner separation length is the most sensitive quantity to upstream distortion, with protrusions tending to increase the separation length and recessions reducing the separation length. Modifications in the separation length of up to 40% are observed. Reductions in peak loads tend to correspond to increases in the corner separation length. The movement of the surface distortion relative to the corner indicates a negligible impact beyond 1.5 distortion lengths from the corner, and the largest impact on the corner separation length occurs when distortion is directly adjacent. These results are an important step toward understanding and quantifying the impact of surface deformations on downstream components. [ABSTRACT FROM AUTHOR]

Accurate resistance performance evaluation is essential to predict the minimum propulsion horsepower required for ships in real sea. Therefore, in this paper, the added resistance performance of K-Supramax in various wave conditions was calculated using CFD (Computational Fluid Dynamics). First, to compare the resistance performance according to the DOF (Degree of Freedom), the added resistance performance in the head regular wave was investigated and compared with the experiment. The 2DOF and 6DOF results in the head regular wave had no significant differences. Second, to compare the resistance performance among various wave conditions, the effect of the heading angle was analyzed by comparing resistance and motion RAOs (Response Amplitude Operators) in bow quartering sea conditions using 6DOF. The added resistance showed the highest value near the resonance frequency of 170°. As the heading angle increased, the added resistance tended to decrease, regardless of the wavelength ratio. Also, the added resistance performance in irregular waves was investigated with reference to the adverse conditions. The spectral method, which linearly superimposes regular wave results, and the added resistance generated during irregular waves directly through CFD were compared. The resistance in irregular waves increased by approximately 92% for the spectral method and by approximately 72% for the direct irregular wave calculation compared to the resistance in calm water. In addition, the PSD (Power Spectral Density) of resistance and the distribution of motion RAOs obtained from direct irregular wave calculations were investigated. [ABSTRACT FROM AUTHOR]

Reynolds-averaged Navier–Stokes simulations are performed for supersonic turbulent flow over a cylinder/flare with upstream surface distortion representative of structural deformation induced via fluid–structural and fluid–thermal–structural behavior. Broad parametric analysis is carried out through the generation of Kriging-response surfaces from a database of general simulations. A posteriori simulations are then carried out at parametric combinations that correspond to extrema in the Kriging response surfaces to gain deeper insights into the interaction between the surface distortion and flow responses. Upstream distortions tend to decrease, rather than increase, the peak pressure and heat flux loads on the flare compared to an undeformed cylinder. Furthermore, decreases in these quantities reach up to O(10%) compared to up to O(1%) for increases. Integrated quantities over the flare are relatively insensitive to upstream distortion. The corner separation length is the most sensitive quantity to upstream distortion, with protrusions tending to increase the separation length and recessions reducing the separation length. Modifications in the separation length of up to 40% are observed. Reductions in peak loads tend to correspond to increases in the corner separation length. The movement of the surface distortion relative to the corner indicates a negligible impact beyond 1.5 distortion lengths from the corner, and the largest impact on the corner separation length occurs when distortion is directly adjacent. These results are an important step toward understanding and quantifying the impact of surface deformations on downstream components.

The Reynolds-averaged Navier–Stokes (RANS) solver was used to calculate, using a test rig to verify the accuracy. The interaction mechanism between different sealed cooling air and gas ingestion at the rotor-stator cavity and chute rim clearance has been investigated. Several groups of representative sealed cooling air flow were selected to explore the cooling efficiency, flow characteristics, tangential and radial velocity ratios in the cavity and the pressure potential field characteristics of trailing edge. The conclusions are obtained: the sealed cooling air flow rate has a significant marginal effect on the sealing effect. The gas ingestion behavior under the small sealed cooling air flow belongs to the disc cavity intrusion, and the intrusion and outflow regions at the of rim clearance are obviously divided into the intrusion characteristic section and the outflow characteristic section. The ingestion behavior under large sealed cooling air flow belongs to clearance ingestion, and the intrusion flow is limited to the chute rim clearance position, which cannot be further penetrated into the cavity. At this time, the clearance area and the cavity area become independent, and the gas ingestion characteristics depend more on the internal flow of the clearance and the vortex structure formed. [ABSTRACT FROM AUTHOR]

Three-dimensional simulations using Reynolds-averaged Navier–Stokes equations were conducted to evaluate wind loads and structural displacements of ground-mounted solar panels under different flow conditions. The panels were arranged in a regular array consisting of 3 rows and 5 columns, with each row comprising 4 × 4 sub-panels inclined at 45°. To conserve computational resources, periodic flow conditions were applied to a single panel by specifying the pressure differential and inlet velocity ranging from 25 to 50 m/s. The fluid-solid coupling, fixed geometry multi-physics field coupling feature was employed to couple the boundary loads due to fluid flow from the fluid to the solid domain. Our results reveal the existence of circulation zones between the panels in the array. The pressure at the upper corners of the solar panel increases sharply with velocity, leading to a larger structural displacement in this region. As the wind speed increases, the safety factors obtained from the simulation for the solar panel support module and the glass panel are 22.8, 8.9, and 5.7 m/s, respectively. And the safety factor of the support frame and support rod junction and the upper row of glass panels decreases significantly. Therefore, the failure characteristics of this part of the structure should be considered in case of a sudden change in wind speed. [ABSTRACT FROM AUTHOR]

This study aims to investigate the aerodynamic analysis of a Darrieus-type vertical axis wind turbine (VAWT) using the Lattice Boltzmann Method (LBM). The objective is to assess the accuracy and performance of the meshless LBM approach in predicting torque coefficients, velocity, turbulence intensity, and vorticity distributions for VAWT aerodynamic analysis. Two turbulence modelling approaches, Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS), are employed to model the flow domain. The central problem revolves around comparing the performance of different turbulence models based on their agreement with experimental results for power and torque coefficients. The findings demonstrate the effectiveness of the WALE turbulence model in achieving the best agreement with experimental data. Overall, the study provides valuable insights into applying LBM in VAWT aerodynamic analysis and highlights the advantages of the meshless approach compared to traditional CFD methods. [ABSTRACT FROM AUTHOR]

This study explores the implementation of physics-informed neural networks (PINNs) to analyze turbulent flow in composite porous-fluid systems. These systems are composed of a fluid-saturated porous medium and an adjacent fluid, where the flow properties are exchanged across the porous-fluid interface. The segregated PINN model employs a novel approach combining supervised learning and enforces fidelity to flow physics through penalization by the Reynolds-averaged Navier-Stokes (RANS) equations. Two cases were simulated for this purpose: solid block, i.e. porous media with zero porosity, and porous block with a defined porosity. The effect of providing internal training data on the accuracy of the PINN predictions for prominent flow features, including flow leakage, channeling effect and wake recirculation was investigated. Additionally, L _2 norm error, which evaluates the prediction accuracy for flow variables was studied. Furthermore, PINN training time in both cases with internal training data was considered in this study. Results showed that the PINN model predictions with second-order internal training data achieved high accuracy for the prominent flow features compared to the RANS data, within a 20% L _2 norm error of second-order statistics in the solid block case. In addition, for the porous block case, providing training data at the porous-fluid interface showed errors of 18.04% and 19.94% for second-order statistics, representing an increase in prediction accuracy by 7% compared to without interface training data. The study elucidates the impact of the internal training data distribution on the PINN training in complex turbulent flow dynamics, underscoring the necessity of turbulent second-order statistics variables in PINN training and an additional velocity gradient treatment to enhance PINN prediction.

Staggered labyrinth seals are used in gas turbines for cooling turbine blades. In this study, numerical analyses were performed to evaluate the discharge coefficients about the shape variables of staggered labyrinth seals. Four shape variables were considered: cavity width (CW), staggered height (GH), staggered width (GW), and staggered position (GP). Changes in the discharge coefficient with the shape variables were analyzed. Strategies were investigated to decrease the discharge coefficient of a staggered labyrinth seal. The discharge coefficient of the optimized staggered labyrinth seal was 37 % smaller than that of a straight labyrinth seal. We hypothesized that the size of the vena contracta and acceleration in the axial direction were related to the discharge coefficient. However, an association between only the GW was not observed. The wall shear stress was sensitive only to the GH and independent of the other shape parameters. [ABSTRACT FROM AUTHOR]

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Darrieus–Landau instability is an essential driving mechanism behind flame acceleration, especially in the absence of turbulence. Effectively quiescent initial conditions are particularly relevant for explosion safety in various process facilities or parts of nuclear power plants. Large-scale industrial facilities pose a considerable challenge for numerical modeling through CFD since applying methods that rely on resolving the internal flame structure to predict the flame dynamics is well outside the limits of today's computational resources. Therefore, in present work, a new scale-adaptive URANS (Unsteady Reynolds-Averaged Navier–Stokes) model for sub-grid closure is introduced. It is aimed at modeling the effects of the Darrieus–Landau instability at a significantly reduced computational cost. Model validation was performed using lean and stoichiometric hydrogen deflagration experiments at medium ( ∼ 1 m) and large ( ∼ 10 m) geometric scales. [ABSTRACT FROM AUTHOR]

Turbofan engine intakes are designed to provide separation-free flow at the fan face over a wide range of operating conditions. But at some off-design conditions, like at high flight speeds and high angles of attack (AoA), the aero engine intake may encounter flow separation. This boundary layer separation inside the nacelle inlet of an aircraft engine can lead to a large number of undesirable outcomes like reduction in fan efficiency, engine stall and high levels of stress on the fan blades. Active flow control is a promising solution to reduce inlet boundary layer separation and the associated fan-face flow distortion at such off-design conditions. By blowing pressurized air into the intake near the separation point, the boundary layer is energized and separation can be controlled. This study investigates the applicability of lip blowing, an active flow control technique, to control intake separation and flow distortion at the fan-face. First, intake separation was triggered in a 3D CFD model based on the NASA Common Research Model (CRM) using high AoA cases at cruise condition (Mach number 0.85, Mass flow capture ratio ∼0.7) and the features of separated flow were analyzed. Thereafter, active flow control was introduce to the intake in the form of two types of lip blowing, direct and pitched blowing. The efficacy of lip blowing at achieving separation control in an ultra high bypass ratio turbofan engine intake has been established through this study. The present paper also examines the significance of blowing parameters like the type of blowing, blowing pressure ratio, and blowing slot dimension, at different angles of attack to identify the critical control parameters. Our research successfully establishes proof of concept by demonstrating the feasibility of using lip blowing for separation control in aero-intakes, via numerical modelling. Furthermore, this study also provides crucial insights regarding the important variables to be considered for future experimental studies, and also for detailed studies covering a wider range of operating and blowing conditions.

Aortic dissection is a life-threatening vascular disease associated with high rates of morbidity and mortality, especially in medically underserved communities. Understanding patients' blood flow patterns is pivotal for informing evidence-based treatment as they greatly influence the disease outcome. The present study investigates the flow patterns in the false lumen of three aorta dissections (fully perfused, partially thrombosed, and fully thrombosed) in the chronic phase, and compares them to a healthy aorta. Three-dimensional geometries of aortic true and false lumens (TLs and FLs) are reconstructed through an ad hoc developed and minimally supervised image analysis procedure. Computational fluid dynamics (CFD) is performed through a finite volume unsteady Reynolds-averaged Navier–Stokes approach assuming rigid wall aortas, Newtonian and homogeneous fluid, and incompressible flow. In addition to flow kinematics, we focus on time-averaged wall shear stress and oscillatory shear index that are recognized risk factors for aneurysmal degeneration. Our analysis shows that partially thrombosed dissection is the most prone to false lumen degeneration. In all dissections, the arteries connected to the false lumen are generally poorly perfused. Further, both true and false lumens present higher turbulence levels than the healthy aorta, and critical stagnation points. Mesh sensitivity and a thorough comparison against literature data together support the reliability of the CFD methodology. Image-based CFD simulations are efficient tools to assess the possibility of aortic dissection to lead to aneurysmal degeneration, and provide new knowledge on the hemodynamic characteristics of dissected versus healthy aortas. Similar analyses should be routinely included in patient-specific hemodynamics investigations, to plan and design tailored therapeutic strategies, and to timely assess their effectiveness. [ABSTRACT FROM AUTHOR]

Via analysis of velocity and stress fields from Reynolds-Averaged Navier–Stokes simulations over diverse complex terrains spanning several continents, in neutral conditions we find displaced areal-mean logarithmic wind speed profiles. The corresponding effective roughness length ( z 0,eff ), friction velocity ( u ∗ ,eff ), and displacement height ( d eff ) characterise the drag exerted by the terrain. Simulations and spectral analyses reveal that the terrain statistics—and consequently d eff , u ∗ ,eff and z 0,eff —can change significantly with flow direction, including flow in opposite directions. Previous studies over scaled or simulated fractal surfaces reported z 0,eff to depend on the standard deviation of terrain elevation ( σ h ), but over real terrains we find z 0,eff varies with standard deviation of terrain slopes ( σ Δ h / Δ x ). Terrain spectra show the dominant scales contributing to σ Δ h / Δ x vary from ∼ 1–10 km, with power-law behaviour over smaller scales corresponding to fractal terrain used in earlier works. The dependence of z 0,eff on σ Δ h / Δ x is consistent with fractal terrain having σ Δ h / Δ x ∝ σ h , as well as classic theory for individual hills. We obtain relationships for z 0,eff , d eff , and u ∗ ,eff in terms of σ Δ h / Δ x , finding that d eff acts as a characteristic length scale within z 0,eff . Considering flow in opposite directions, use of upslope statistics did not improve z 0,eff predictions; sheltering effects likely require more sophisticated treatment. Our findings impact practical applications and research, including micrometeorological flow, computational fluid dynamics, atmospheric model coupling, and mesoscale and climate modelling. We discuss limitations of the z 0,eff formulations developed herein, and provide recommendations for practical use. [ABSTRACT FROM AUTHOR]

Accurate resistance performance evaluation is essential to predict the minimum propulsion horsepower required for ships in real sea. Therefore, in this paper, the added resistance performance of K-Supramax in various wave conditions was calculated using CFD (Computational Fluid Dynamics). First, to compare the resistance performance according to the DOF (Degree of Freedom), the added resistance performance in the head regular wave was investigated and compared with the experiment. The 2DOF and 6DOF results in the head regular wave had no significant differences. Second, to compare the resistance performance among various wave conditions, the effect of the heading angle was analyzed by comparing resistance and motion RAOs (Response Amplitude Operators) in bow quartering sea conditions using 6DOF. The added resistance showed the highest value near the resonance frequency of 170°. As the heading angle increased, the added resistance tended to decrease, regardless of the wavelength ratio. Also, the added resistance performance in irregular waves was investigated with reference to the adverse conditions. The spectral method, which linearly superimposes regular wave results, and the added resistance generated during irregular waves directly through CFD were compared. The resistance in irregular waves increased by approximately 92% for the spectral method and by approximately 72% for the direct irregular wave calculation compared to the resistance in calm water. In addition, the PSD (Power Spectral Density) of resistance and the distribution of motion RAOs obtained from direct irregular wave calculations were investigated.

The present paper attempts to study the flood wave propagation at a right-angled combining open channel junction utilizing the three-dimensional (3D) transient Reynolds-averaged Navier-Stokes (RANS) equations. The present study advocates using the 3D model over the depth-averaged two-dimensional (2D) model by comparing simulations obtained from 3D and 2D models for steady flows. The 3D model is validated against the experimental results of the flood routing in a single reach channel, available in the literature. The flood wave at the channel inlet is generated by a half-cycle of the sinusoidal function. Three different cases (Cases 1, 2, and 3) are considered by applying the flood wave at the inlet of the main channel, tributary channel, and both the channels, respectively. The steady-state junction flow with equal discharge in both the upstream channels is considered as the initial condition for the flood wave simulations. The rising flood flow of the main channel offers huge flow blockage to the tributary channel flow in Case 1, while vice versa in Case 2. The blockage causes significant flow accumulation leading to the stage rise. In Case 2, the flow reversal occurs as the flow in the main channel is entirely blocked by the rising flood flow of the tributary channel. The interplay of the flow blockage by the main channel to the tributary channel and vice versa results in water accumulation and release, alternatively. The maximum stage rise occurs in Case 3 due to the combined effects of the rising flood wave and flow blockage, simultaneously. The previous flood routing studies at the channel junction have disregarded the momentum equation. This may not be accurate as momentum exchange occurs between the main and tributary channel flow. Considering the dynamic interaction between the approaching flows, the present paper attempts to study the flood wave propagation at a right-angled combining open channel junction utilizing the fully three-dimensional numerical model. Three different simulation cases considered for investigating the flood wave propagation demonstrate the impact of the main channel flood wave on the tributary flow and vice versa. The alternate amplification and attenuation of the flow discharge in both the upstream channels continue to happen due to the interplay of the blockage offered by the main channel to the tributary channel and vice versa before the junction flow attains the base flow condition. The results of the present study improve the understanding of flood wave propagation at the channel junction. [ABSTRACT FROM AUTHOR]

The demand for new propeller designs has increased alongside the development of new technology, such as urban aircraft and large unmanned aerial vehicles. In order to experimentally identify the performance of a propeller, a wind tunnel that provides the operating flow is essential. However, in the case of a meter class or larger propeller, a large wind tunnel is required and the related equipment becomes heavy; therefore, it is difficult to implement in reality. For this reason, propeller studies have been conducted via reduced models. In this case, it is necessary to investigate the different performance outputs between the full- and model-scale propellers due to the size difference. In the current study, a method is proposed to investigate the difference in the aerodynamic performance caused by the difference in propeller scale using VLM and RANS calculations, and the differences are analyzed. The wind tunnel test also verified the propeller performance prediction method. The boundary of aerodynamic performance independent of the Reynolds number could be predicted through the VLM based on the ideal fluid assumption. From the RANS calculations, it was possible to present the difference in the aerodynamic performance when propellers of the same geometry with different ratios were operated using different Reynolds numbers. It was confirmed that each numerical method matched well with the wind tunnel test results in the range of the advance ratio that produced the maximum efficiency, and from the results, it was possible to observe the change in aerodynamic performance that differed according to the scale change. [ABSTRACT FROM AUTHOR]

A series of numerical simulations were performed to study the discharge coefficient based on the geometric parameters of a stepped labyrinth seal that sealed the secondary flow path of a gas turbine. In contrast with straight-through seals, stepped labyrinth seals introduce additional geometrical parameters related to the steps. In this study, three shape variables were observed: step height (SH), position, and cavity width (CW). The sensitivity to the leakage flow of the shape variable in the stepped labyrinth seal was analyzed. The mechanism for improving the sealing performance of stepped labyrinth seals was investigated. The results indicated that the stepped labyrinth seal exhibited up to 17.9% higher leakage-suppression performance than the straight labyrinth seal. Seals with large discharge coefficients had a large vena contracta upstream of each tooth structure and a rapidly accelerated axial velocity in the radial direction. We could observe that the discharge coefficient changed according to the flow field in the cavity. The wall shear stress was sensitive to the SH but not to the CW or step position. [ABSTRACT FROM AUTHOR]

This study aims to investigate the aerodynamic analysis of a Darrieus-type vertical axis wind turbine (VAWT) using the Lattice Boltzmann Method (LBM). The objective is to assess the accuracy and performance of the meshless LBM approach in predicting torque coefficients, velocity, turbulence intensity, and vorticity distributions for VAWT aerodynamic analysis. Two turbulence modelling approaches, Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS), are employed to model the flow domain. The central problem revolves around comparing the performance of different turbulence models based on their agreement with experimental results for power and torque coefficients. The findings demonstrate the effectiveness of the WALE turbulence model in achieving the best agreement with experimental data. Overall, the study provides valuable insights into applying LBM in VAWT aerodynamic analysis and highlights the advantages of the meshless approach compared to traditional CFD methods.

The computational approaches of CFD are more powerful than the analytical solutions for high-speed compressible flows over a flat plate. A small number of expensive experimental data can be generated to aid high-speed vehicle design. However, CFD can be used to simulate a large variety of flows with different freestream and wall conditions in a cost-effective manner. The current work aims to numerically calculate the turbulent boundary layer flows over a flat plate at different Mach numbers in the range of 2–8 at different wall conditions and unit Reynolds numbers. The Reynolds-averaged Navier–Stokes method with k − ω turbulence model is applied to resolve the flow over the flat plate at zero angle of attack. The computed skin friction coefficient and Stanton number are compared with the available experimental data in the literature. The calculated results indicate some agreement with the experimental data. An increase in the Mach number and wall temperature decreases the skin friction and the Stanton number. A polynomial curve fit data estimation is proposed for skin friction under adiabatic wall conditions for Mach numbers in the range of 2–8. Numerical simulations over compression corner flows are also presented in the present work. The freestream Mach number influences the thickness of the subsonic layer in the undisturbed boundary layer on the flat plate in compression corner flows. The higher freestream Mach number results in a lower subsonic thickness near the wall, leading to a small separation bubble and lower peak heat transfer in shock/boundary-layer interaction flows. [ABSTRACT FROM AUTHOR]

In this study, the performance of a twin-screw propeller under the influence of the wake field of a fully appended ship was investigated using a coupled Reynolds-averaged Navier—Stokes (RANS)/boundary element method (BEM) code. The unsteady BEM is an efficient approach to predicting propeller performance. By applying the time-stepping method in the BEM solver, the trailing vortex sheet pattern of the propeller can be accurately captured at each time step. This is the main innovation of the coupled strategy. Furthermore, to ascertain the effect of the wake field of the ship with acceptable accuracy, a RANS solver was developed. A finite volume method was used to discretize the Navier—Stokes equations on fully unstructured grids. To simulate ship motions, the volume of the fluid method was applied to the RANS solver. The validation of each solver (BEM/RANS) was separately performed, and the results were compared with experimental data. Ultimately, the BEM and RANS solvers were coupled to estimate the performance of a twin-screw propeller, which was affected by the wake field of the fully appended hull. The proposed model was applied to a twin-screw oceanography research vessel. The results demonstrated that the presented model can estimate the thrust coefficient of a propeller with good accuracy as compared to an experimental self-propulsion test. The wake sheet pattern of the propeller in open water (uniform flow) was also compared with the propeller in a real wake field. [ABSTRACT FROM AUTHOR]

Aortic dissection is a life-threatening vascular disease associated with high rates of morbidity and mortality, especially in medically underserved communities. Understanding patients’ blood flow patterns is pivotal for informing evidence-based treatment as they greatly influence the disease outcome. The present study investigates the flow patterns in the false lumen of three aorta dissections (fully perfused, partially thrombosed, and fully thrombosed) in the chronic phase, and compares them to a healthy aorta. Three-dimensional geometries of aortic true and false lumens (TLs and FLs) are reconstructed through an ad hoc developed and minimally supervised image analysis procedure. Computational fluid dynamics (CFD) is performed through a finite volume unsteady Reynolds-averaged Navier–Stokes approach assuming rigid wall aortas, Newtonian and homogeneous fluid, and incompressible flow. In addition to flow kinematics, we focus on time-averaged wall shear stress and oscillatory shear index that are recognized risk factors for aneurysmal degeneration. Our analysis shows that partially thrombosed dissection is the most prone to false lumen degeneration. In all dissections, the arteries connected to the false lumen are generally poorly perfused. Further, both true and false lumens present higher turbulence levels than the healthy aorta, and critical stagnation points. Mesh sensitivity and a thorough comparison against literature data together support the reliability of the CFD methodology. Image-based CFD simulations are efficient tools to assess the possibility of aortic dissection to lead to aneurysmal degeneration, and provide new knowledge on the hemodynamic characteristics of dissected versus healthy aortas. Similar analyses should be routinely included in patient-specific hemodynamics investigations, to plan and design tailored therapeutic strategies, and to timely assess their effectiveness.

The demand for new propeller designs has increased alongside the development of new technology, such as urban aircraft and large unmanned aerial vehicles. In order to experimentally identify the performance of a propeller, a wind tunnel that provides the operating flow is essential. However, in the case of a meter class or larger propeller, a large wind tunnel is required and the related equipment becomes heavy; therefore, it is difficult to implement in reality. For this reason, propeller studies have been conducted via reduced models. In this case, it is necessary to investigate the different performance outputs between the full- and model-scale propellers due to the size difference. In the current study, a method is proposed to investigate the difference in the aerodynamic performance caused by the difference in propeller scale using VLM and RANS calculations, and the differences are analyzed. The wind tunnel test also verified the propeller performance prediction method. The boundary of aerodynamic performance independent of the Reynolds number could be predicted through the VLM based on the ideal fluid assumption. From the RANS calculations, it was possible to present the difference in the aerodynamic performance when propellers of the same geometry with different ratios were operated using different Reynolds numbers. It was confirmed that each numerical method matched well with the wind tunnel test results in the range of the advance ratio that produced the maximum efficiency, and from the results, it was possible to observe the change in aerodynamic performance that differed according to the scale change.

This work is focused on the aerodynamic shape optimization (ASO) of airfoils with the aim of attaining natural laminar flow (NLF) designs. The two-equation Amplification Factor Transport (AFT) model is utilized for an accurate prediction of the transitional boundary layer flows. The NLF designs are achieved by utilizing two different objective functions. In the first approach, the conventional drag minimization problem is solved with a target lift coefficient. In addition, a second approach is proposed in this work that directly aims at delaying the transition onset on both the pressure and suction sides, thus expanding the natural laminar flow region around the airfoil. It is shown that by utilizing a sigmoid fitting of the turbulence index profile, the transition onset locations can be accurately predicted in a differentiable and smooth fashion, which is essential to the adjoint-based sensitivity analysis of the RANS solver. The efficacy of the proposed technique for NLF design has been tested for NACA 0012 and RAE 2822 airfoils at moderate lift coefficients. Results have shown that a significantly lower drag count can be achieved by delaying the transition onset locations compared to the case where only a drag minimization is sought. Additionally, the transition onset locations on both sides of the airfoil are delayed using our proposed technique which results in a significant expansion of the natural laminar flow region. [ABSTRACT FROM AUTHOR]

Since ship-bank interaction affects the manoeuvrability of a ship navigating close to a bank, the determination of hydrodynamic derivatives is of great importance to assess the ship manoeuvrability. To obtain the hydrodynamic derivatives of the KVLCC2 model ship with different water depths and ship-bank distances, the simulation of PMM tests are carried out using an unsteady Reynolds-Averaged Navier–Stokes (RANS) based solver. Hybrid dynamic mesh technique is proposed to realize the simulation of pure yaw tests in confined water. Studies on the grid convergence and time-step-size convergence are firstly performed. Hydrodynamic derivatives for the ship in different water depths and ship-bank distances are compared. The course stability is investigated based on time-domain simulations and eigenvalue analysis, and the results show that the ship-bank interaction and shallow water effect have a remarkable influence on the course stability.

The present paper reports numerical simulation of turbulent flow over a square cylinder using a novel scale resolving computational fluid dynamics technique named Partially-Averaged Navier–Stokes (PANS), which bridges Reynolds-Averaged Navier–Stokes (RANS) with Direct Numerical Simulation (DNS) in a seamless manner. All stream-wise and wall normal mean velocity components, turbulent stresses behavior have been computed along the flow (streamwise) as well as in transverse (wall normal) direction. The measurement locations are chosen based on the previous studies so that results could be compared. However, the Reynolds number (Re) of the flow is maintained at 21,400 and K – ω turbulence model is considered for the present case. All the computations are performed in OpenFOAM framework using a finite volume solver. Additionally, turbulent kinetic energy variations are presented over a wide range of measurement planes in order to explain the energy transfer process in highly unsteady turbulent flow field. The fluctuating root mean square velocities in the streamwise as well as in the wall normal direction have been discussed in the present work. It has been found that Partially-Averaged Navier–Stokes (PANS) model is capable of capturing the properties of highly unsteady turbulent flows and gives better results than Reynolds-Averaged Navier–Stokes (RANS). The results obtained using Partially-Averaged Navier–Stokes (PANS) are quite comparable with Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) data available in literature. The partially-averaged Navier–Stokes results are compared with our simulated Reynolds-Averaged Navier–Stokes (RANS) results, available experimental as well as numerical results in literature and it is found to be good in agreement. [ABSTRACT FROM AUTHOR]

In this paper, numerical modeling of the movement and dispersion of pollutant emissions between houses as well as the effect of a continuous barrier on the spread of pollutants was considered. To solve this problem, a system of Reynolds-averaged Navier–Stokes equations was used, and various turbulent models were applied to close this equation system. To test the mathematical model, the numerical algorithm and the choice of the optimal turbulent model, the test problem was solved numerically. The obtained numerical results were compared with experimental data and the results of modeling by other authors. After checking the mathematical model, the numerical algorithm and the choice of the optimal turbulent model, the main problem describing the process of pollutant emissions between houses using continuous grass barriers was solved. In this problem, the distribution of pollutants was considered when using herbal barriers and the optimal height for these barriers was chosen. For the simulation, the RNG k-epsilon turbulence model was applied, which was chosen from the obtained results of the test problem. The numerical simulation results were compared with the obtained calculated data using different heights of solid grass barriers. And it was found that when using a solid grass barrier with a height of 0.1 m, the concentration value drops by more than 1.5 times compared with that without using a barrier, and further increasing the height of the barrier does not give the desired result. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation of motion and dispersion of pollutant emissions into the atmosphere under real atmospheric conditions were considered. To solve this problem, a system of Reynolds-averaged Navier–Stokes equations was used, and the standard k-epsilon and SST k-omega turbulence models were used to close this system of equations. Moreover, the test problem was solved numerically to verify the mathematical model and numerical algorithm. The obtained numerical results were compared with the experimental data and modeling results of well-known authors. A proven mathematical model and numerical algorithm was used to describe the process of pollutant emissions from Ekibastuz SDPP (Ekibastuz State District power plant) chimneys and the spread of CO2 in the air flow field under real atmospheric conditions. For this problem, four different speed regimes (the first—0.5 m/s and 1 m/s, the second—1 m/s and 1.5 m/s, the third—2 m/s and 4 m/s, and the fourth—4 m/s and 5 m/s), as well as three different temperature regimes (constant temperature, decrease temperature, and temperature inversion) were considered. [ABSTRACT FROM AUTHOR]

The NO x -O 3 photochemical reactive air pollutant dispersion around an isolated building bears significant scientific and engineering implications. The present work extends the investigation to the role of turbulence models and building aspect ratio, providing valuable insights for future numerical investigations and building complex design. Validated against wind tunnel experiments, a serial Computational Fluid Dynamics (CFD) investigation was conducted with physiochemical coupling, including one large eddy simulation with near-wall resolution (LES-NWR) and three Reynolds-averaged Navier-Stokes (RANS) viscosity models (i.e., standard k-ε model (STK), renormalization group k-ε model (RNG), realizable k-ε model (RLZ)). The numerical models were assessed regarding the predictive capability of the mean pollutant concentration and velocity fields. Results show that the areas of high NO concentration are generally indifferent to the selection of turbulence models. Elsewhere, the RLZ provides the most comparable results to the LES-NWR, whereas the RNG and STK underestimate the reverse flow in the building wake and produce subpar predictions at the roof. The RNG also yields the weakest prediction by overestimating the lateral separation bubbles' influence. Furthermore, changing the aspect ratio has negligible effects on the stream and spanwise dispersion of the highly concentrated pollutant. However, the building width plays a more decisive role in constraining the streamwise dispersion than the building height. Doubling the building length also slows down the shrinkage of recirculation, leading to a steep deduction in the streamwise dispersion along the building height. • Pollutant dispersion of NO x -O 3 photochemical reactions in a building's near wake. • High-fidelity CFD simulation involving pollutants' physiochemical coupling. • Evaluation and comparison of RANS and LES for CFD model selection guidance. • Fundamental pollutant dispersion mechanisms around isolated building with different aspect ratios. [ABSTRACT FROM AUTHOR]

• Examination of complex 3D flow structure within a coal power plant SCR reactor. • Magnetic resonance velocimetry (MRV) utilized to validate RANS CFD. • Asymmetric recirculation zone observed within the catalytic reactor. • Integral flow parameters were not affected by Reynolds number. • Flow bias caused by recirculation induces uneven de-NO x reactions. A selective catalytic reduction (SCR) reactor is commonly used to remove nitrogen oxides (NO x) from coal-fired boilers. Uniformity of the flow passing through the catalyst layer is important for increasing denitrification (de-NO x) efficiency. In order to examine flow uniformity, this study conducted an experimental and numerical analysis of the complex internal flow within a realistic SCR model. Magnetic resonance velocimetry (MRV) was utilized to obtain non-invasive measurements of three-dimensional three-component average velocity and validate Reynolds-averaged Navier-Stokes (RANS) numerical simulations. The computational results showed similar overall flow structure compared with the MRV results. Parameters representing flow quality such as relative standard deviation (RSD) and recirculation zone strength (RZS) were calculated by integrating the flow field. These parameters have the largest value after the straightener area and decrease towards the catalyst reactor, and are not significantly affected by Reynolds number upstream of the catalyst layer. The recirculation zone size was analyzed using spanwise uniformity and skewness indicators. As the recirculation zone induces biased flow, the non-reacted NO x concentration was more prominent in the outlet zone opposite of the recirculating area in the corresponding actual on-site SCR reactor. Based on this finding, a meaningful correlation between flow maldistribution and de-NO x reaction could be deduced. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to develop a validated numerical model of a water vortex power plant that serves as a digital twin for further studies such as assessments of the ethohydraulic characteristics or the performance of such devices. The reference for the validation process is a large-scale hydraulic installation equipped with a full-scale water vortex power plant prototype installed in Dresden (Germany), where flow field measurements were carried out using three-dimensional Acoustic Doppler Velocimetry. The numerical model was implemented within the software package Star-CCM+. The unsteady, two-phase flow was solved with the Reynolds-Averaged Navier–Stokes equations in a Eulerian Multiphase approach, deploying a Volume of Fluid method to describe the free-surface flow. Water level and flow velocities were systematically compared in key areas of the device, demonstrating that the simulation is in good agreement with experimental observations. Relative differences are limited to at most 4% regarding water height in the system, and even the much more challenging velocity fields are reproduced with typical relative errors of roughly 10%. This validates the ability of the model to model the challenging flow conditions found in a water vortex power plant, enabling subsequent studies of the characteristics of this power plant concerning fish migration.

Summary: We present a hybridized discontinuous Galerkin (HDG) method for the incompressible Reynolds‐averaged Navier‐Stokes equations coupled with the Spalart‐Allmaras one‐equation turbulence model. The method extends upon an HDG method recently introduced by Rhebergen and Wells for the incompressible Navier‐Stokes equations. With a special choice of velocity and pressure spaces for both element and trace degrees of freedom (DOFs), the method returns pointwise divergence‐free mean velocity fields and properly balances momentum and energy. We further examine the use of different polynomial degrees and meshes to see how the order of the scalar eddy viscosity affects the convergence of the mean velocity and pressure fields, specifically for the method of manufactured solutions. As is standard with HDG methods, static condensation can be employed to remove the element DOFs and thus dramatically reduce the global number of DOFs. Numerical results illustrate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

This study numerically investigates the propagation characteristics of hazardous noxious substances (HNSs) spilled from transport ships and suggests the metal model for predicting the HNS propagation velocity varied with the current velocity and HNS density. The commercial computational fluid dynamics (CFD) code ANSYS FLUENT (V. 17.2) was used for two-dimensional simulation based on the Reynolds-averaged Navier–Stokes (RANS) equation together with the standard k–ε model. The scalar transport equation was also solved to estimate the spatial and transient behaviors of HNS. The main parameters to analyze the near-field propagation characteristics of HNSs spilled from the ship were layer thickness, HNS concentration, and propagation velocity. It was found that advection becomes more dominant in propagating an HNS layer that becomes thinner as the current velocity increases. When the current velocity increased beyond a certain level (~0.75 m/s), the mixing effect made the HNS layer less dense but thicker. Consequently, lower-density HNS causes increased HNS concentrations at sea level. As the current velocity increased, the concentration distribution became homogeneous regardless of HNS density. In particular, the second-order response surface model provided for three variables on the basis of the numerical results for 15 cases with the use of the general least-squares regression method, showing a good fit. This model would be useful in estimating the propagation velocity of HNS spilled from a ship. [ABSTRACT FROM AUTHOR]

Numerical works have been conducted to investigate the effect of nozzle geometries on the discharge coefficient. Several contoured converging nozzles with finite radius of curvatures, conically converging nozzles and conical divergent orifices have been employed in this investigation. Each nozzle and orifice has a nominal exit diameter of 12.7×10−3 m. A 3rd order MUSCL finite volume method of ANSYS Fluent 13.0 was used to solve the Reynolds-averaged Navier–Stokes equations in simulating turbulent flows through various nozzle inlet geometries. The numerical model was validated through comparison between the numerical results and experimental data. The results obtained show that the nozzle geometry has pronounced effect on the sonic lines and discharge coefficients. The coefficient of discharge was found differ from unity due to the non-uniformity of flow parameters at the nozzle exit and the presence of boundary layer as well.

A turbulent Couette flow over a wavy surface is subject to a detailed parametric study in which three parameters—Aspect Ratio, Wave Slope and Reynolds number—are independently varied over an order of magnitude to investigate their influence on the flow. Stdk−ε turbulence model with enhanced wall functions is used to simulate all cases in the study and the results are validated against experimental data as well as analytical theories pertaining to flow over wavy surfaces. Gross flow properties such as mean velocity profiles, mass flow rate, shear stress and pressure on the walls, as well as turbulent flow characteristics such as inner-wall coordinates, log-law fit, eddy viscosity profiles and turbulence kinetic energy across the domain, are presented and their corroboration with existing literature is discussed. The effect of the three parameters on the flow variables is investigated. It is observed that while all response flow variables scale monotonically with a progressive change in the parameters, there are certain flow characteristics that can be ascribed exclusively to one of the three parameters. The study also discusses the influence of the top plate, a much-needed discussion that seems to be absent in most literature pertaining to Couette flow in wavy channels.

Ducted propellers are unconventional systems that are usually adopted for ship propulsion. These devices have recently been studied with medium-fidelity computational fluid dynamics code (based on the potential flow hypothesis) with promising results. However, these tools, even though they provide a good prediction of the forces and moments generated by the blades and the duct, are not able to provide insight into the flow field characteristics due to their crude flow approximations. On the contrary, modern high-fidelity viscous-based computational fluid dynamics codes could give a better description of the near and far-field flow of these particular devices. In the present paper, forces and the most significant features of the flow field around two ducted propellers are analyzed by means of both experimental and computational fluid dynamics approaches. In particular, accelerating and decelerating ducts are considered, and we demonstrate the ability of the adopted solver to accurately predict the performance and the flow field for both types. These results, in particular for the less-studied decelerating duct, designate CFD as a useful tool for reliable designs.

Effects of spontaneous condensation of moist air on the shock wave dynamics around butterfly valves in transonic flows are investigated by experimental and numerical simulations. Two symmetric valve disk shapes namely- a flat rectangular plate and a mid-plane cross-section of a prototype butterfly valve have been studied in the present research. Results showed that in case with spontaneous condensation, the root mean square of pressure oscillation (induced by shock dynamics) is reduced significantly with those without condensation for both shapes of the valves. Moreover, local aerodynamic moments were reduced in case with condensation which is considered to be beneficial in torque requirement in case of on/off applications of valves as flow control devices. However, total pressure loss was increased with spontaneous condensation in both the valves. Furthermore, the disk shape of a prototype butterfly valve showed better aerodynamic performances compared to flat rectangular plate profile in respect of total pressure loss and vortex shedding frequency in the wake region.

Shock wave-boundary layer interactions (SWBLI) are observed in several practical high-speed internal flows, such as compressor blades, turbine cascades, nozzles and so on. Shock induced oscillations (SIO), aerodynamic instabilities so-called buffet flows, flutter, aeroacoustic noise and vibration are the detrimental consequences of this unsteady shock-boundary layer interactions. In the present study, a numerical computation has been performed to investigate the compressible flow characteristics around a 12% thick biconvex circular arc airfoil in a two dimensional channel. Reynolds averaged Navier-Stokes equations with two equation k-ω shear stress transport (SST) turbulence model have been applied for the computational analysis. The flow field characteristics has been studied from pressure ratio (ratio of back pressure, pb to inlet total pressure, p01) of 0.75 to 0.65. The present computational results have been compared and validated with the available experimental data. The results showed that the internal flow field characteristics such as shock wave structure, its behavior (steady or unsteady) and the corresponding boundary layer interaction are varied with pressure ratio. Self-excited shock oscillation was observed at certain flow conditions. Moreover, the mode of unsteady shock oscillation and its frequency are varied significantly with change of pressure ratio.

Liquid microjet impingement cooling has shown the potential to be the solution for heat removal from electronic devices such as very-large-scale integration (VLSI) chips. The post-impingement dynamics of the jet, specifically the interaction between the liquid fronts on the surface engendered by the jets is a critical criterion improving the heat transfer characteristics. While some seminally important experimental studies have investigated this attribute, the amount of accurate data and analysis is limited by the shortcomings of real-life experiments. In this article, numerical investigations into the fluid dynamics and heat transfer in microjet cooling systems are carried out. Specifically, this paper addresses the question regarding the necessary fidelity of the simulations. Different Reynolds-averaged Navier−Stokes (RANS) models are compared to the Large Eddy Simulations (LES) simulation and the potential fidelity of different eddy-viscosity-based closures is clearly shown. Recommendations are made regarding the RANS closures that should give the best performance. It is demonstrated that the transition Shear Stress Transport (SST) model and k - ω SST model both show excellent ability to predict the local or average Nu, and also local level pressure coefficient f with less than 5% difference in the range of 30 < Red < 4000, compared with the reference LES model. For the experimental measurements in the range of 130 < Red < 1400, the LES model, transition SST model and k - ω SST model all show less than 25% prediction error. Moreover, it is shown that the validity of the unit cell assumption for the temperature and flow distribution depends on the flow rate.

A validated standard k-ε model was used to investigate the effects of ground heating on ventilation and pollutant transport in a three-dimensional (3D) street canyon. Air entered the street canyon from the upper regions of side surfaces and most areas of the top surface and left from the lower regions of side surfaces. Ground heating enhanced the mean flow, ventilation, and turbulence, and facilitated pollutant reduction inside street canyons. The transport patterns in a street canyon that included a pollutant source (PSC) and a target street canyon downstream (TSC) were different. The pollutant did not enter the PSC, and turbulent diffusion dominated pollutant outflow at all boundaries. The pollutant entered the TSC from most regions of the side surfaces and exited from lower regions of the side surfaces and the entire top surface. Air convection dominated pollutant transport at the side surfaces, and its contribution increased significantly with ground temperature; Furthermore, turbulent diffusion dominated pollutant outflow for the top surface, and its contribution increased slightly with ground heating. As revealed by an analysis of both the total pollutant flow rates and air flow rates, although air/pollutant exchange between the TSC and outer space occurred primarily through the side surfaces, the increase in air inflow from the top surface reduced the pollutant concentration inside the street canyon when the ground temperature increased. The top surface played a major role in improving air quality in a 3D environment with ground dispersion. This study supplied valuable suggestions for urban planning strategies. The analyzing method used in this research is helpful for the pollutant transport investigations in urban areas.

In this study, the Reynolds-averaged Navier⁻Stokes (RANS) method and a model experimental test in a towing tank are used to investigate the unsteady hydrodynamic performance of L-type podded propulsion under different oblique flow angles and advance coefficients. The results show that the load of the operative propeller increases with oblique flow angle and the bracket adds resistance to the pod due to the impact of water flow, leading to a reduced propeller thrust coefficient with increased oblique flow angle. Under a high advance coefficient, the speed of increase of the pressure effect is higher than that of the viscosity effect, and the propeller efficiency increases with the oblique flow angle. The nonuniformity of the inflow results in varying degrees of asymmetry in the horizontal and vertical distributions of the propeller blade pressure. Under high oblique flow angle, relatively strong interference effects are seen between venting vortexes and the cabin after blades, leading to a disorderly venting vortex system after the blade. The numerical simulation results are in good agreement with the experimental values. The study findings provide a foundation for further research on L-type podded propulsors.

This study numerically investigates the propagation characteristics of hazardous noxious substances (HNSs) spilled from transport ships and suggests the metal model for predicting the HNS propagation velocity varied with the current velocity and HNS density. The commercial computational fluid dynamics (CFD) code ANSYS FLUENT (V. 17.2) was used for two-dimensional simulation based on the Reynolds-averaged Navier–Stokes (RANS) equation together with the standard k–ε model. The scalar transport equation was also solved to estimate the spatial and transient behaviors of HNS. The main parameters to analyze the near-field propagation characteristics of HNSs spilled from the ship were layer thickness, HNS concentration, and propagation velocity. It was found that advection becomes more dominant in propagating an HNS layer that becomes thinner as the current velocity increases. When the current velocity increased beyond a certain level (~0.75 m/s), the mixing effect made the HNS layer less dense but thicker. Consequently, lower-density HNS causes increased HNS concentrations at sea level. As the current velocity increased, the concentration distribution became homogeneous regardless of HNS density. In particular, the second-order response surface model provided for three variables on the basis of the numerical results for 15 cases with the use of the general least-squares regression method, showing a good fit. This model would be useful in estimating the propagation velocity of HNS spilled from a ship.

Round jets impinging at multiple impingement angles were considered for this study to gain better understanding of the parameters affecting resultant jet growth and velocity distribution. Work done by the authors previously on single jet has helped to establish that the SST (Shear Stress Transport) k-ω model is the ideal turbulence model for predicting flow characteristics of jets exiting a fully developed pipe at low Reynolds number. Hence, for the study of impinging jets, SST k-ω turbulence model was used to study the velocity and jet growth characteristics. Based on the mesh obtained from the grid sensitivity study, jets impinging at 30, 45 and 60 degrees at Reynolds number of 7500 were numerically analyzed. It was observed that the profile of the resultant jet closely matched with the prediction of elliptical profile predicted by past researchers. In addition, it was seen that higher jet growth was predicted in the case of jets impinging at a higher impingement angle.

Accurate flow ratings at water-control structures are essential for water-resource management. This paper presents an approach to obtain numerically generated data using computational fluid dynamics (CFD) to complement field measurements needed to improve spillway flow-rating formulas. The procedure to generate CFD flow data described herein is based on solving Reynolds-Averaged Navier-Stokes equations using the κ-ε turbulence closure model with the free surface resolved by the volume of fluid (VOF) method. The steps for setting the computational domain, generating the mesh, selecting the boundary conditions, and choosing a convergence criteria for the simulations are discussed. The turbulence closure model and VOF method for the present application are verified with data from laboratory measurements of submerged jet flow below a gate and in a sharp open-channel bend. CFD flow data generation is validated with laboratory and field measurements for gated ogee spillways in south Florida. The results presented here demonstrate that CFD is a plausible alternative to complement data measured at prototype structures and reduced-scale models for the purpose of calibration and validation of rating formulas used for real-time flow monitoring at prototype water-control structures. [ABSTRACT FROM AUTHOR]