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In this study, high-Fidelity Large eddy simulation (LES) data was used to create a surrogate turbulence model to enhance the estimation of turbulent heat flux in a Reynolds averaged Navier Stokes (RANS) solver for film cooling applications. The LES simulation (A flat plate film cooling application with a Reynolds number of 17,382, a blowing ratio of 1 and a density ratio of 2) was validated by comparison with experimental data. A correlation analysis was performed to identify the most influential parameters, and temperature gradient, velocity gradient, turbulent dissipation rate, shear strain rate, and turbulent viscosity ratio were selected as the most effective parameters. A second model was developed to create a Galilean-invariant model that remains unaffected by changes in the coordinate system. Neural network was applied to the LES training data to propose a modified surrogate dynamic turbulent Prandtl number to be applied to the k − ε realizable RANS simulation. The first surrogate model was implemented to two different geometries, one geometry was a flat plate film cooling similar to the training data but with different flow conditions, and another one was a more complex geometry with pressure gradient. The second model was only implemented on the second geometry and produced similar results. The surrogate models predicted a more accurate thermal field near the cooling wall (up-to 58 % error reduction) with a computational time complexity similar to the base RANS solver.

More extreme, frequent and longer heat waves negatively affect people all around the world, and especially inhabitants of urban areas which face even higher temperatures due to the urban heat island effect. A precondition to develop adaptation strategies to counteract adverse effects of heat in cities is to gain knowledge about the urban temperature distribution. One approach that has been applied in various cities is the implementation of dense urban temperature measurement networks. Since financial resources are usually limited, such networks consist of cost-effective measurement devices whose (daytime) data quality is prone to errors due to radiative influences. This was also the case in Zürich, Switzerland, where an urban temperature network with 272 measurement stations was operated from 2019 to 2021. In this study, we present a radiation correction method to enhance the data quality for practical use. Applying the proposed correction method led to a reduction in mean RMSE from 1.47 K to 0.57 K and in the overall mean bias from +0.88 K to +0.04 K. Following from that, we use the corrected database for two application cases: i) As a spatially and temporally high-resolution validation dataset for the physics-based large eddy simulation model PALM and ii) as input data for a geostatistical land use regression model. The analysis shows that the daytime radiation correction is crucial to detect the negative bias of the PALM model, which is most pronounced in the highly built-up area of Zürich, and to enhance the quality of the daytime land use regression. The developed radiation correction presented in this study can also be applied for other urban temperature networks that are facing similar challenges.

Abstract There is growing interest in discovering interpretable, closed‐form equations for subgrid‐scale (SGS) closures/parameterizations of complex processes in Earth systems. Here, we apply a common equation‐discovery technique with expansive libraries to learn closures from filtered direct numerical simulations of 2D turbulence and Rayleigh‐Bénard convection (RBC). Across common filters (e.g., Gaussian, box), we robustly discover closures of the same form for momentum and heat fluxes. These closures depend on nonlinear combinations of gradients of filtered variables, with constants that are independent of the fluid/flow properties and only depend on filter type/size. We show that these closures are the nonlinear gradient model (NGM), which is derivable analytically using Taylor‐series. Indeed, we suggest that with common (physics‐free) equation‐discovery algorithms, for many common systems/physics, discovered closures are consistent with the leading term of the Taylor‐series (except when cutoff filters are used). Like previous studies, we find that large‐eddy simulations with NGM closures are unstable, despite significant similarities between the true and NGM‐predicted fluxes (correlations >0.95). We identify two shortcomings as reasons for these instabilities: in 2D, NGM produces zero kinetic energy transfer between resolved and subgrid scales, lacking both diffusion and backscattering. In RBC, potential energy backscattering is poorly predicted. Moreover, we show that SGS fluxes diagnosed from data, presumed the “truth” for discovery, depend on filtering procedures and are not unique. Accordingly, to learn accurate, stable closures in future work, we propose several ideas around using physics‐informed libraries, loss functions, and metrics. These findings are relevant to closure modeling of any multi‐scale system.

In the pursuit of decarbonization, the reduction of greenhouse gas emissions from power generation through gas turbine (GT) engines plays a crucial role in the whole industrial sector. As industries strive to transition towards cleaner energy sources, the design and optimization of novel GT burners require a deep comprehension of the complex interaction between fluid dynamics and combustion processes embedded within the system. Computational Fluid Dynamics (CFD) plays a pivotal role in these processes by providing valuable insights into the complex flow patterns, flame topology, and stability limits within the combustor. Concurrently, the burner design phase necessitates a considerable number of simulations to ascertain flame stability limits under various burner designs and operating conditions. Therefore, it is imperative to control computational costs while ensuring a high level of accuracy. The present work is focused on a comprehensive comparative analysis of two widely employed turbulent combustion closure models: the Flamelet Generated Manifold (FGM) and the Artificially Thickened Flame (ATF). Both models utilize extended versions with specific modifications aimed at effectively addressing their respective limitations. The investigation is performed through a Large Eddy Simulation (LES) based CFD analysis within the context of a lean premixed burner designed by Baker Hughes and operated with methane at atmospheric pressure. The primary benchmark for numerical validation will be provided by detailed chemiluminescence images from a test campaign conducted by the University of Florence, thereby yielding valuable insights into flame topology and positioning. Furthermore, potential disparities in the flow field and fuel concentration at the burner exit between the two models will be revealed.

In previous work, a Large Eddy Simulation turbulence (LES) algorithm was developed for finite element-based computational fluid dynamics, using a hybrid continuous-discontinuous Galerkin scheme. The test case for this was a backward-facing step, which is a well-known example with published experimental results for validation. The results of this simulation were used to produce temporal statistics, such as averaged velocity and Reynolds stress profiles, and time-series data. In conjunction with previous published work by the authors, this data here will allow validation of other LES models and as well as detailed comparisons with the original model.

In response to growing environmental and ecological awareness, eco-friendly in-stream structures such as vanes have been implemented in different parts of the world to enhance stream conditions. FLUENT (ANSYS) was used to perform three-dimensional large eddy simulation to investigate the effect of the vanes permeability rate on flow characteristics. To evaluate the numerical model accuracy, numerical and experimental free surface profiles compared. It is observed that simulated free surface profiles agree reasonably well with measured values. The effect of different permeability rates is obvious in the flow characteristics such as depth-averaged velocity distribution, tip velocity variations, formation of the secondary flows in the flow field, turbulent kinetic energy, and mean kinetic energy contours. On average, maximum velocity values in the flow field is 1,54 times the approach velocity. Tip velocity decreases up to 30,6 % for the 70,0 % permeable vane. Maximum turbulent kinetic energy and mean kinetic energy for the 70,0 % permeable vane decrease up to 58,0 % and 43,3 %, respectively. Generally significant velocity and flow pattern variations around the impermeable vane can be attributed to the local effect of the vane structure and channel cross sectional constriction in comparison to the permeable vanes.

[Introduction] Combining mesoscale numerical model and large eddy simulation (LES) model, numerical sumulation of sub-kilometer-scale project unit placement is carried out, which takes into account atmospheric boundary layer changes. It provides offshore wind turbine projects with high-efficiency power generation placement schemes. [Method] This study converted the mesoscale numerical weather simulation results into boundary conditions for the input of the LES model and introduced model parameters reflecting the operation of an actual wind farm into the LES simulation. The numerical sumulation experiments of the ambient wind field in the wind farm region was carried out under the consideration of the change of the actual atmospheric boundary layer, and the results of the refined simulation scheme of this wind field were evaluated based on the observation data collected from the wind farm. [Result] The simulation results indicate that by converting the results of the mesoscale weather model into the dynamic drive which is read by the LES model and simulating the wind field where the wind farm is located based on the model, the simulation results are able to replicate the changes in the external wind field after passing through the wind farm and the wake generated within the wind turbine fleet, as well as its impact on the internal wind field of the wind farm. The root mean square error of wind speed simulation at the hub of wind turbines is 1.54 m/s. [Conclusion] The refined wind field simulation scheme, which takes into account the variation of mesoscale meteorological elements and the impact of wind farms on the ambient wind field, can provide guidance for the design phase of actual projects.

In-vessel retention through external reactor vessel cooling (IVR-ERVC) is a severe accident management (SAM) strategy that has been adopted and used in many nuclear reactors such as AP1000, APR1400, and light water reactor etc. Some reactor accidents have raised concerns about nuclear reactors among residents, leading to a decrease in residents' acceptability and many studies on SAM are being conducted. Experiments on IVR-ERVC are almost impossible due to its specificity, so fluid characteristics are analyzed through BALI experiments with similar condition. In this study, computational fluid dynamics (CFD) via Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) for BALI experiments were performed. Steady-state CFD analysis was performed on three turbulence models, and SST k-ω model was in good agreement with the experimental measurement temperature within the maximum error range of 1.9%. LES CFD analysis was performed based on the RANS analysis results and it was confirmed that the temperature and wall heat flux for depth was consistent within an error range of 1.0% with BALI experiment. The LES CFD analysis results were compared with those of the Lagrangian-based solver. LES matched the temperature distribution better than SOPHIA, but SOPHIA calculated the position of boundary between stratified layer and convective layer more accurately. On the other hand, Lagrangian-based solver predicted several small eddy behaviors of the convective layer and LES predicted large vortex behavior. The vibration characteristics near the cooling part of the BALI experimental device were confirmed through Fast Fourier Transform (FFT) investigation. It was found that the power spectral density for pressure at least 10 times higher near the side cooling than near the top cooling.

Momentum diffusion and kinetic energy transfer in turbomachinery have always been significant issues, with a considerable impact on the performance of the bladeless Tesla turbine. This radial turbine shows high potential for various energy applications, such as Organic Rankine Cycle or combined heat and power systems. Analyzing the flow inside the gap between the corotating disks of the Tesla turbine presents challenges due to several factors, including submillimeter length scales, variations in flow cross-section, interactions of body forces arising from rotation with turbulence, interactions between the turbine’s inlet nozzles and rotor, and moving walls. General design parameters, e.g., number of nozzles, also pose a challenge in order to achieve the full potential of this turbine. In this research, two different variants of the supply system are considered with six and forty nozzles. To minimize computational expenses, a portion of the entire domain is considered. The flow in each domain, consisting of one inlet nozzle and a segment of one gap between the disks, is examined to reveal the complexity of flow structures and their impact on the Tesla turbine performance. Large Eddy Simulation (LES) with the Smagorinsky subgrid-scale model is used to verify the results of the k-ω Shear-Stress Transport (SST) turbulence model in the first case study with six nozzles. Analyzing the results indicates that the k-ω SST model provides valuable insights with appropriate accuracy. The second case study, with forty nozzles, is simulated using the k-ω SST turbulence model. The research compares flow structure, flow parameters, and their impact on the system’s performance. From the comparison between the k-ω SST turbulence model and LES simulation, it was observed that although the k-ω SST model slightly overestimates the general parameters and damps fluctuations, it still provides valuable insights for assessing flow structures. Additionally, the mesh strategy is described, as the LES requirements make this simulation computationally expensive and time-consuming. The overall benefits of this method are discussed.

In fuel assemblies of pressurized water reactors (PWRs), mixing-vane spacer grids are extensively employed to array fuel rods and enhance inter- and intra-subchannel mixing. The turbulent flow downstream of spacer grids is essential knowledge to support the design of spacer grids and mixing vanes. As a high- fidelity approach for turbulence simulation, large eddy simulation (LES) results are assessed with the high-resolution flow field measured with particle image velocimetry (PIV). The LES results reveal a mixing vane effect on vortex structures and Reynolds stresses. The mechanism of vortex generation at the mixing vanes and the development downstream of the spacer grid are visualized by the Q-criterion. The distributions of the root mean square fluctuating velocity and Reynolds stresses decay rapidly downstream of the spacer grid. The secondary flow intensity downstream of the spacer grid predicted by LES is evaluated and follows an exponentially decaying law with distance from the spacer grid. [ABSTRACT FROM AUTHOR]

AbstractThe large Eddy Simulation approach is applied to simulate turbulent mixed convection of nanofluid through a vertical channel. Nanofluid consists of nano-encapsulated phase change material (NEPCM) nanofluid (5% n-octadecane/water) and hybrid nanofluid (1% CuO + 5% n-octadecane/water). The wall-adapting local eddy-viscosity model is used. The computations are performed at a friction Reynolds number of 180. The turbulence statistics quantities including normalized mean velocity and temperature, root mean square of velocity and temperature fluctuations, Reynolds shear stress and turbulent heat flux are estimated. The agreement between computed mean velocity and temperature profiles and turbulence statistics by direct numerical simulation data is good. The present numerical results show that addition of nanoparticles into pure water increases normalized mean stream-wise velocity, fluctuations of velocity and temperature, Reynolds shear stress and turbulent heat flux. By adding NEPCM and CuO nanoparticles into pure water normalized velocity fluctuations grow in three directions, as a result of which normalized Reynolds shear stress augments. Enhancement of normalized root mean square of velocity fluctuations can cause a strengthening exchange of mass and momentum, and leads to augmentation of heat transfer. The average decrease in normalized mean temperature is 8.5% for NEPCM nanofluid and 12% for hybrid nanofluid. The results indicate that hybrid nanofluid containing CuO and NEPCM nanoparticles shows a better thermal performance than nanofluid containing only NEPCM nanoparticles and pure water. This makes hybrid nanofluid in presence of NEPCM particles to be a possible choice in cooling process applications. [ABSTRACT FROM AUTHOR]

Sunken square is a semi-open public space that has been gaining popularity in urban planning and designs. Its semi-open design is beneficial to ventilation of the connected underground spaces, but it is also subject to potential exposure to ground-level traffic pollutants. To evaluate the semi-open design's influence on the balance between underground ventilation efficiency and the pollutant exposure, this study uses large eddy simulation (LES) to simulate turbulent wind flow characteristics and pollutant dispersion in a typical sunken square. The sunken square is connected to two indoor spaces with single-sided opening, and the design features of staircase and arcade are further tested for their influences on the wind flow field. The air change rate per hour (ACH, h−1) is adopted to quantify the ventilation efficiency of the two connected indoor spaces. Results show that the staircases amplify wind velocities for the indoor spaces but also bring higher pollutant concentrations inside together. Moreover, the design of the arcade at the opening prompts the vortex to shift towards the entrance, leading to a heightened concentration of pollutants. Meanwhile, the effective ACH is mostly contributed by the turbulent diffusion (ACHt), while the mean flow (ACHm) has much less effect on the ventilation of the indoor spaces. These findings of this study provide references for sunken square design. [ABSTRACT FROM AUTHOR]

The effect of the injection pressure on the dynamic flow characteristics of a lean direct injection gas turbine combustor under nonreactive conditions during liquid fuel atomization was investigated. The location of the internal recirculation core, size of the vortex breakdown bubble, and shape of the precessing vortex core and shear layer were confirmed by increasing the fuel injection pressure. It was found that as the fuel injection pressure increased, the momentum of the droplets increased. The tangential momentum of the constant main air swirl flow transferred to the droplets increased as the pressure increased, causing the swirl strength to decrease. It was confirmed that, as the swirl intensity decreased with increasing injection pressure, the shape of the precessing vortex core generated in front of the combustor became shorter, and the size of the central recirculation area also decreased. [ABSTRACT FROM AUTHOR]

Large-eddy simulation of subsonic round jet impinging on a flat circular plate is performed at Mach number 0.9 and Reynolds number 25,000, based on the diameter and centerline velocity of the jet for two impingement distances h of 6r0 and 8r0 using high-order compact finite difference scheme. The complex flow phenomena associated with the impinging jet flowfield are studied. The power spectral density (PSD) of instantaneous pressure reveals a discrete impingement tone. Dynamic mode decomposition (DMD) of the velocity and pressure is also done for both cases to extract the most dominant modes of the flow. The fundamental impingement tone frequency obtained from the PSD of pressure is identical to that of the first dominant pressure mode obtained from DMD. Both axisymmetric and semihelical modes are present for the h=8r0 case, but only axisymmetric modes are there in the h=6r0 case, and it is noted that the modes corresponding to the fundamental tone have an axisymmetric structure. Also, one dominant mode showing the wall jet structures denoting the liftoff of fluid from the wall after impingement at some radial distance away from the stagnation region is present in both impingement distance cases. [ABSTRACT FROM AUTHOR]

A novel formulation of the vortex particle method (VPM) is developed for large-eddy simulation (LES) in a meshless scheme that is numerically stable. A new set of VPM governing equations are derived from the LES-filtered Navier-Stokes equations. The new equations reinforce the conservation of angular momentum by resizing vortex elements subject to vortex stretching. In addition to the VPM reformulation, a new anisotropic dynamic model of subfilter-scale (SFS) vortex stretching is developed. This SFS model is well suited for turbulent flows with coherent vortical structures, where the predominant cascade mechanism is vortex stretching. The mean and fluctuating components of turbulent flow and Reynolds stresses are validated through the simulation of a turbulent round jet. The computational efficiency of the scheme is showcased in the simulation of an aircraft rotor in hover, showing our meshless LES to be 100 times faster than a mesh-based LES with similar fidelity. The implementation of our meshless LES scheme is released as open-source software, called FLOWVPM. [ABSTRACT FROM AUTHOR]

The lack of observational data in Taklamakan Desert makes it very difficult to study its unique boundary layer structure. As a common means of supplementing observational data, the mesoscale boundary layer parameterization scheme in the numerical model method is difficult to capture small-scale turbulent processes, which may lead to large deviations in simulation. In order to obtain more accurate simulation data of desert atmospheric boundary layer, nested LES into WRF (WRF-LES) was configured to simulate the seasonal variations in Taklamakan Desert. By comparing LES with the conventional boundary layer parameterization scheme, the error characteristics between the two schemes are analyzed. The results show that LES exhibits superior performance in solving key atmospheric features such as small-scale processes and low-level jet streams. The simulation results in winter and summer have great uncertainty due to the boundary condition errors, respectively. LES also shows the maximum and minimum optimization degree in summer and winter, respectively, while the simulation results in spring and autumn are relatively stable. In the analysis of turbulence parameters, there are clear seasonal differences in turbulence characteristics, and the intensity of turbulence in summer is significantly higher than that in other seasons. When turbulent activity is strong, the difference in potential temperature and horizontal wind speed simulated between the two schemes is closely related to intense turbulent kinetic energy in LES. More accurate turbulence reproduced in LES leads to the better potential temperature and horizontal wind speed simulations in summer. In addition, large-scale cloud systems can lead to considerable simulation bias. Neither scheme can accurately simulate the cloud emergence process, and large differences between the two schemes occur at this point. [ABSTRACT FROM AUTHOR]

The frequency characteristics of lung sounds have great significance for noninvasive diagnosis of respiratory diseases. The rales in the lower respiratory tract region that can provide rich information about symptoms of respiratory diseases are not clear. In this paper, a three-dimensional idealized bifurcated lower respiratory tract geometric model, which contains 3rd to 13th generation (G3–G13) bronchi is constructed, where Re ∼ 10 1 - 10 3 , and then the large eddy simulation and volume of fluid are used to study the fluid flow characteristics. Ffowcs Williams and Hawkings model are subsequently used to study the frequency characteristics of rale of different generations of bronchi. The results showed that bronchial blockage and sputum movement will enhance the turbulence intensity and vortex shedding intensity of flow. The dominant frequency and highest value of sound pressure level (SPL) of rhonchi/moist crackles decrease with the increase of bronchial generation. The change rates of dominant frequency of rhonchi / moist crackles in adjacent generations were 5.0 ± 0.1 ~ 9.1 ± 0.2% and 3.1 ± 0.1 ~ 11.9 ± 0.3%, respectively, which is concentrated in 290 ~ 420 Hz and 200 ~ 300 Hz, respectively. The change rates of SPL of rhonchi/moist crackles were 8.8 ± 0.1 ~ 15.7 ± 0.1% and 7.1 ± 0.1 ~ 19.5 ± 0.2%, respectively, which is concentrated in 28 ~ 50 dB and 16 ~ 32 dB, respectively. In the same generation of bronchus (e.g., G8, G9) with the same degree of initial blockage, the dominant frequency and SPL of moist crackles can be 3.7 ± 0.2% and 4.5 ± 0.3% slightly higher than that of rhonchi, respectively. This research is conducive to the establishment of a rapid and accurate noninvasive diagnosis system for respiratory diseases. [ABSTRACT FROM AUTHOR]

Turbulent spray combustion in a generic kerosene-fueled single-cup combustor at typical idle and cruise conditions of an aeroengine are studied with Large Eddy Simulations (LES) using Lagrangian spray and finite-rate chemistry combustion modeling. Three reaction mechanisms of varying complexity are used to model the combustion chemistry. The choice of turbulence-chemistry interaction model is shown to affect the results significantly. The impact of the choice of chemical reaction mechanism and the difference in operating conditions are gauged in terms of time-averaged flow, spray, and combustion characteristics as well as unsteady behavior. Good agreement between LES predictions and experimental results are generally observed but with a notable dependence on the choice of chemical reaction mechanism. The mechanism specifically targeting Jet A displays the best agreement. The choice of reaction mechanism is further demonstrated to influence the flow and thermoacoustics in the combustor, resulting in different thermoacoustic modes dominating. The spray cone is found to be too narrow and thin, an inaccuracy which could be remedied by either making the injection method more empirical or by introducing additional models. [ABSTRACT FROM AUTHOR]

The cooling fan is one of the important noise sources for new energy vehicles, and the research on its aerodynamic and aeroacoustic characteristics is of great help to improve the noise, vibration and harshness performance of new energy vehicles. However, most of these studies focus on the impeller, and little consideration has been given to the study of the shroud. Based on the coupling calculation method of large eddy simulation and the Ffowcs-Williams and Hawkings acoustics model, the aerodynamic and aeroacoustic characteristics in a cooling fan with the shroud are investigated at flow rates from 0.623 kg/s to 1.019 kg/s (where 0.865 kg/s is the flow rate corresponding to the best efficiency point). The accuracy of numerical simulation results is verified by the grid independence verification and the comparison of experimental data. Research shows that several large-scale vortex structures are observed in the clearance between the impeller and the shroud. The maximum peak-to-peak values of pressure fluctuation at different flow rates occur in the intermediate section or outlet section of the shroud. Although the shroud contributes relatively less to the far field noise, its different distribution may change the position of the maximum sound pressure level. The dominant frequency of pressure fluctuation equals the blade passage frequency (BPF) and the maximum SPL is around the BPF, both of which are independent of flow rates. The maximum SPL and the amplitude of the dominant frequency decrease as the flow rate increases. [ABSTRACT FROM AUTHOR]

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Today, aviation has grown significantly in importance. However, the challenge of flight delays has become increasingly severe due to the need for safe separation between aircraft to mitigate wake turbulence effects. The primary emphasis of this investigation resides in elucidating the evolutionary attributes of wake vortices in homogeneous isotropy turbulence. The large eddy simulation (LES) method is used to scrutinize the dynamic evolution of wake vortices engendered by an A333 aircraft in the atmospheric milieu and assess its ramifications on the ARJ21 aircraft. The research endeavor commences by formulating an LES methodology for the evolution of aircraft wake vortices, integrating adaptive grid technology to reduce the necessary grid volume significantly. This approach enables the implementation of axial and non-axial grid adaptive refinement, leading to more accurate simulations of both axial and non-axial vortices. Numerical simulations are conducted using the LES approach to scrutinize three distinct rates of turbulence dissipation amidst the ambient atmospheric turbulence, and the results are juxtaposed with Lidar measurements (Wind3D 6000 LiDAR) of wake vortices acquired at Chengdu Shuangliu International Airport (CTU). Subsequently, the rolling moment of the following aircraft is calculated, and three-dimensional hazard zones are determined for the A333. It is found that during the approach phase, the wake turbulence separation minima for an ARJ21 (CAT-F) following an A333 (CAT-B) is 3.35 NM, which represents a reduction of approximately 33% compared to ICAO RECAT (Wake Turbulence Re-categorization). The findings validate the dependability of the fine-grained mesh used in the vortex core region, engendered through the adaptive grid method, which proficiently captures the Crow instability and the interconnected phenomena of vortices in the numerical examination of aircraft wake. The safety of wake encounters primarily depends on the magnitude of environmental turbulence and the development of structural instability in wake vortices. [ABSTRACT FROM AUTHOR]

It is very important for the wind-resistant design of high-rise buildings to assess wind-induced vibrations efficiently. The Lattice Boltzmann Method-based Large Eddy Simulation and Fluid–Structure Interaction techniques are used to identify the surface wind pressure and wind-induced dynamic response of a CAARC standard high-rise building. Compared with wind tunnel tests, a detailed analysis of the accuracy of simulated wind pressures and base moments of the CAARC model are discussed under multiple wind direction angles. The differences between one-way and two-way Fluid–Structure Interaction simulations are compared under two different reduced wind velocities. The research results show that the simulated mean surface wind pressures of building under seven wind direction conditions have an error within 15% compared to probe measurements, and the average and root mean square base bending moments agree well with the wind tunnel tests. The top transverse wind-induced vibrations of the buildings are significantly larger when the reduced wind velocity reaches 4.6, indicating that aerodynamic damping effects on structural responses should not be overlooked. The research findings of this article provide valuable technical references for the application of LBM methods in the wind load effect assessments of high-rise buildings. [ABSTRACT FROM AUTHOR]

Trash racks installed at hydropower plants cause head losses that reduce energy output. Previous research has thoroughly investigated head losses through both experimental and field studies. However, only a limited number of numerical studies have been performed, which have shown significant simplifications in terms of model complexity. In this study, the head loss coefficients ξ of circular bar trash racks (CBTRs) were analyzed using 3D Large Eddy Simulation (LES). Specifically, a single submerged bar oriented perpendicular to the flow direction was studied under homogeneous inflow conditions while (i) the blocking ratio P was varied between 0.043 and 0.444, and (ii) the flow velocity U was varied between 0.3 and 1.0 m/s. The model parameters were selected primarily based on the extensive literature on flow past circular cylinders, particularly at a Reynolds bar number Reb of 3900. To ensure the validity of the parameters, systematic independence tests were performed, including simulations with three and five bars in the computational domain. The results confirmed the suitability of 3D LES as an appropriate tool to determine ξ of CBTRs. In general, ξ decreased continuously with decreasing P and increased with increasing U when Reb ≥ 3981, which is consistent with comparable flow parameters observed in previous studies of flow past circular cylinders. Notably, the study found that the empirical formulas used for comparison tended to underestimate ξ when P was relatively low. Finally, the potential of the presented approach for future applications was discussed in detail. [ABSTRACT FROM AUTHOR]

The dispersion of particulate pollutants around buildings raises concerns due to adverse health impacts. Accurate prediction of particle dispersion is important for evaluating health risks in urban areas. However, rigorous validation data using particulate tracers is lacking for numerical models of urban dispersion. Many prior studies rely on gas dispersion data, questioning conclusions due to differences in transport physics. To address this gap, this study utilized a combined experimental and computational approach to generate comprehensive validation data on particulate dispersion. A wind tunnel experiment using particulate tracers measured airflow, turbulence, and particle concentrations around a single building, providing reliable but sparse data. Validated large eddy simulation expanded the data. This combined approach generated much-needed validation data to evaluate numerical particle dispersion models around buildings. Steady Reynolds-averaged Navier–Stokes (SRANS) simulations paired with Lagrangian particle tracking (LPT), and drift-flux (DF) models were validated. SRANS had lower accuracy compared to LES for airflow and turbulence. However, in this case, SRANS inaccuracies did not prevent accurate concentration prediction when LPT or a Stokes drift-flux model were used. The algebraic drift-flux model strongly overpredicted the concentration for large micron particles, indicating proper drift modeling was essential. [ABSTRACT FROM AUTHOR]

The present study is aimed to investigate the effect of temperature on the flow field. In this study, LES (large eddy simulation) and HWA (hot wire anemometry) are used to investigate the time-averaged and instantaneous flow field in the cyclone at different temperatures. The numerical results agree well with the experiment data. The results show that temperature has an impact on both the time-averaged flow field and the fluctuations of the flow field. To investigate the effect of temperature on flow field fluctuations, we first reveal the mechanism of flow field fluctuations. The effect of temperature on vortex motion and tangential velocity fluctuation is analyzed, and a mathematical model for predicting the freqeuncy of vortex core precession at different temperatures is proposed, f T / f 0 = k (T 0 / T) 0.125 (1 + m) . The Q criterion is used to identify the vortex in the cyclone. When the temperature is high, the vortex core undergoes a typical vortex breakdown phenomenon at the lower part of the cyclone separator: the vortex core breaks up into a double helix shape. This is the reason for the disappearance of the negative pressure region, the decrease in tangential velocity and the weak fluctuation of tangential velocity in the dipleg at high temperature. • LES model is used to simulate the flow at different temperatures. • HWA is used to measure the instantaneous tangential velocity. • Q criterion is applied to analyze vortex motion in the cyclone. [ABSTRACT FROM AUTHOR]

In this study, the generality and prediction accuracy of a generalised series model for the large eddy simulation of premixed and non-premixed turbulent combustion is explored. The model is based on the Taylor series expansion of the chemical source term in scalar space and implemented into OpenFOAM. The mathematical model does not depend on combustion regimes and has the correct limiting behaviour. The numerical error sources are also outlined and analysed. The model is first applied to a piloted methane/air non-premixed jet flame (Sandia Flame D). The statistical (time-averaged and RMS) results agree well with the experimental measurements, particularly with regard to the mixture fraction, velocity, temperature, and concentrations of major species CH4, CO2, H2O, and O2. However, the concentrations of the intermediates CO and H2 are over-predicted, due to the limitations of the reduced reaction mechanism employed. Then, a Bunsen-piloted flame is simulated. Most of the statistical properties of both the reactive species and progress variables are well reproduced. The only major discrepancy evident is in the temperature, which is probably attributed to the experimental uncertainties of temperature fields in the pilot stream. These findings demonstrate the model's generality for both a premixed and non-premixed combustion simulation, as well as the accuracy of prediction of reactive species distribution. [ABSTRACT FROM AUTHOR]

As modern aeroengine combustors advance towards high temperatures, afterburners are inevitably affected by diminished oxygen content in incoming flows, thus affecting combustion efficiency, instability, and flammability limits. In this study, the dynamic combustion characteristics of V-shaped bluff body-stabilised diffusion flames were investigated using a large eddy simulation method with an oxygen mass fraction range of 14–23% and temperatures ranging from 900 to 1100 K. The results show the significant effects of oxygen content and inflow temperature on the flame/flow behaviours downstream of the bluff-body flame holder. In a separated shear layer, two distinct modes of flow/flame shedding are observed when varying the oxygen content and inflow temperature. The results show that BVK instability governs the far-field wake flow/flame features, whereas the oxygen concentration and temperature significantly affect their oscillation amplitudes. In addition, variations in the incoming oxygen content and temperature shift the axial position of the transition from KH instability to BVK instability. Finally, a spectral analysis is conducted to investigate the characteristics of pressure and heat release pulsations under different scenarios. This study highlights the importance of oxygen content on the combustion dynamics of bluff body-stabilised diffusion flames at various temperatures, which is essential for optimising combustion efficiency and stability in practical applications. [ABSTRACT FROM AUTHOR]

Sand disasters can adversely impact on the operational safety of railway projects. To investigate eolian sand movement characteristics in the wind–sand environment around bridge–subgrade transition sections, in this study, we examine vortex and particle motion characteristics in eolian sand flow fields based on the large eddy simulation (LES) technique and discrete phase model (DPM) while proposing corresponding protection measures for this particular railway section. The results reveal that these methods can be employed to simulate turbulent flow fields. The deposition morphology of particles resembles a wavy ribbon, and the presence of horseshoe–shaped and conical vortices in the wind field affects the deposition of particles. Moving particles are deflected toward the side of the passageway under the bridge. Horizontal and vertical retaining walls are designed to control the wind speed and sand movement. The former obstructs particles, creating a low-velocity zone around the wall, while the latter prevents particle deflection. These protection measures can reduce the saltation distance of sand particles by up to 42.9%. The particle velocity is largely reduced to 0 ~ 2.5 m/s, and only a few small-sized particles (d < 0.35 mm) are transported in suspension. The designed T-shaped retaining wall can effectively prevent sand particles from deviating, achieving a protection rate of 99.85%, with only 0.81% of the sand particles entering the area of the railway operation. [ABSTRACT FROM AUTHOR]

Flow around a cylinder is an important research problem in fluid mechanics. However, studies on traveling wave wall (TWW) flow control for the wake generated by the flow around a 3D cylinder remain limited. This study performs large eddy simulation (LES) to investigate the wake characteristics of flow around a three-dimensional (3D) circular cylinder with the TWW. The influence of the main control parameters of TWW on the aerodynamic forces and wake of the 3D cylinder is analyzed. The wake characteristics of the 3D cylinder at Re = 4 × 104 are obtained, and the traveling wave propagating downstream is achieved on the rear surface of the 3D cylinder using dynamic mesh. The control effects of wave amplitude, number of waves, and wave velocity of the traveling wave on the aerodynamic forces of the cylinder are analyzed, and the optimal control parameter combination is determined. The results demonstrate that the TWW control method completely eliminates the spanwise 3D flow characteristics of the cylinder when the amplitude ratio, number of waves, and velocity ratio are 0.02, 4, and 1.5, respectively. Moreover, it effectively suppresses the flow separation on the cylinder surface, eliminates the wake vortex, and suppresses vortex-induced vibration (VIV). [ABSTRACT FROM AUTHOR]

In this paper, a large eddy simulation (LES) method was used to conduct a study on single and tandem jets in a crossflow, focusing particularly on their trajectory, penetration, and interaction. The numerical model was validated with an experimental test campaign. Examination of the time-averaged flow field allowed both the velocity and the tangential angle of the jet trajectories to be examined. In addition, the penetration depth of the jet based on a scalar transport model was analyzed. The unsteady flow characteristics around the trajectories were studied using both the power spectral density (PSD) function and a spectral proper orthogonal decomposition (SPOD). The results show that the upstream jet's trajectory changes little as a function of spacing, while the downstream jet deflects as a result of the influence of the counterrotating vortex pair. In addition, the curve height of the tandem jet trajectories is significantly higher than that of the single jet. The height of the trajectory formed by the tandem jets can reach four times that of the single jet, and the penetration depth of the tandem jets can be 2.8 times that of the single jet. Meanwhile, when the spacing between the two jets is small, the coherent structures tend toward the upstream jet distribution, and the fluctuation frequency after mixing is dominated by the upstream jet. With the increase of spacing, the fluctuation frequency after mixing is greatly affected by the downstream jet, and the frequency decreases. Furthermore, when the dimensionless spacing D′ is 5.67, the frequency difference between both jets is minimal and the coherent structures are significantly reduced, indicating that flow mixing is optimal and stable. [ABSTRACT FROM AUTHOR]

This research endeavors to study the kinetic behavior of hydrogen explosion flames as they pass through confined spaces with varying obstacle passage lengths using Large Eddy Simulation (LES). The model of premixed flame was customized adopting the OpenFOAM library built upon the evolution of progress variables. By considering the turbulence-induced wrinkling and stretching effects, this study accounts for the resulting increase in flame velocity. The numerical findings managed to correctly match the experimental data. Longer obstacle passages were found to give the flame more acceleration time, resulting in a higher peak propagation velocity and pressure rise rate, according to the study. The first and second peak velocity ratios were 1.09 and 1.46 for the ducts with passage lengths of 3.0 H and 0.5 H, respectively, and the proportion of the pressure rise rate was 1.26. The analysis of vortex dynamics reveals that the vorticity distribution range and intensity are proportional to the length of the obstacle channel, where the baroclinic torque and gas expansion effects are much higher than the contribution of viscous dissipation to vorticity. The study uncovered that during obstacle-induced flame acceleration and propagation, the flame is affected by the coupling effect of RayleighTaylor instability (RTI) and Kelvin-Helmholtz instability (KHI) mechanisms. [ABSTRACT FROM AUTHOR]

Turbulence-radiation interaction (TRI) arises from the highly non-linear coupling between fluctuations of radiative intensity and fluctuations of temperature and chemical composition of the medium. It is well-recognized that neglecting turbulent fluctuations of the latter scalars when computing the mean radiation field, as is standard in Reynolds-Averaged Navier-Stokes (RANS) simulations, leads to mispredictions of the radiative heat fluxes and the radiant fraction in as much as one order of magnitude. Conversely, the importance of TRI in large eddy simulations (LES)--i.e., the effect of subfilter-scale (SFS) fluctuations on the filtered radiation field--has only started to be investigated in the last decade. The present text reviews the knowledge gathered so far on the subject. The instantaneous and the spatially filtered forms of the radiative transfer equation (RTE) are presented, and the unresolved correlations resulting from the filtering operation are discussed. Models for accounting for SFS-TRI are surveyed, with the most popular ones (namely, probability density function-based methods and empirical approximations) reviewed in detail. An appraisal of the literature on the importance and characteristics of SFS-TRI is performed, with special attention given to turbulent jet diffusion flames and pool fires, which are the two configurations for which SFS-TRI has been studied the most. The main findings of these studies are summarized, and recommendations are given on directions of future works on the subject. [ABSTRACT FROM AUTHOR]

Non-zonal methods of hybrid Reynolds Averaged Navier–Stokes (RANS) equations-Large Eddy Simulation (LES) with subfilter transport equations enable to simulate turbulent flows out of spectral equilibrium on relatively coarse grid resolution. They can operate from RANS to LES depending on a control parameter linked to the grid step size. Variational analysis gives a useful framework to specify the functional dependence of this parameter to the grid size. This is the case for the partially integrated transport modelling method originally established in spectral space for homogeneous turbulence. The partitioning control function then monitors the ratio of the subfilter part to the total turbulent energy and the same process is developed in the present work for the thermal or transported scalar variance as well. So, we demonstrate here that this control function mechanism can be derived by variational calculus from a mathematical physics formalism developed both for first-order and second-order moment closures. We show that the result is entirely consistent with the spectral model derivation made in previous papers and that this approach can be transposed to almost any subfilter transport model developed in hybrid RANS-LES methodology in full generality. As a result, it will be evidenced also that resolved turbulent diffusion terms play a significant role in the acting mechanisms of turbulence and cannot be therefore neglected, even if these terms do not explicitly appear in LES subfilter closure because they are computed by the simulation itself and not modelled by the subfilter model. In addition, numerical simulations have been performed for illustrating the theoretical results of the variational analysis. [ABSTRACT FROM AUTHOR]

Large Eddy Simulations of recessed central-duct coaxial injectors under transcritical and two-phase conditions are detailed in this paper, with the objective of assessing the ability of recently develop models (Schmitt (Flow. Turbul. Combust. 105, 159–189, 2020), Pelletier et al. (Computers. Fluids. 206, 104588, 2020)) to recover the experimental observations of an augmentation of the flame expansion rate and its dynamics due to the recess. The simulated cases correspond to the LOx/GH 2 Mascotte A10 and C10, both operating at 10 bar with two-phase flow conditions, and Mascotte C60, injected under transcritical conditions in a chamber at 60 bar (Habiballah et al. (Combust. Sci. Technol. 178, 101–128, 2006)). Cases A10 and C10 qualitatively reproduce the experimental visualizations. However, the simulation with recess for case C60 produces a more disrupted inner jet and a shorter flame than in the experiment. In addition, a fine grid resolution is necessary to capture the absolute instability in this case. Case C60 is then examined. It is observed in particular that heat release rate distribution is importantly modified once the LOx injector is recessed, nearly doubled up to 10 LOx injector diameters. This huge increase of heat release has two origins: (1) an enhanced turbulent mixing in the near injector region due to an increased injector exit velocity because of the thermal expansion in the recessed part, in line with the model proposed by Kendrick et al. (Combust. Flame. 118, 327–339, 1999); (2) a larger flame surface because of the quicker destabilization and larger spreading rate of the flame at the injector exit. [ABSTRACT FROM AUTHOR]

Large eddy simulations have been conducted to study upward transitional flows and heat transfer characteristics of supercritical CO2 in a vertical mini-channel. The numerical simulation was carried out on a modified buoyantPimpleFOAM solver in OpenFOAM 7, and was verified using experiment data. Numerical results indicate that increasing the Grashof numbers can reduce the flow stability and make the flow transition earlier. There are four stages of heat transfer in the transition process, i.e., weakened, improved, recovered and normal heat transfer. These heat transfer phenomena in the transition process were explained from three perspectives: thermal boundary layer theory, turbulent transport and pseudo-boiling theory. Heat transfer enhancement during transition is related to the transport of supercritical molecular clusters, and these molecular clusters are regarded as pseudo-bubbles in pseudo-boiling theory. The flow pattern of the pseudo-phases in the dia-Widom process contains single-phase flow, steady pseudo-film flow, unsteady pseudo-film flow, partial pseudo-bubbles flow and flocculent pseudo-film flow. Pseudo-bubbles have similar behaviors to subcritical bubbles, i.e., break-up, deformation, condensation and coalescence. Relevant researches in this work are favorable for understanding the heat transfer mechanism of supercritical fluids during flow transition. [ABSTRACT FROM AUTHOR]

We present results of implicit large eddy simulation (LES) and different Reynolds-averaged Navier–Stokes (RANS) models of the MTU 161 low pressure turbine at an exit Reynolds number of 90 000 and exit Mach number of 0.6. The LES results are based on a high-order discontinuous Galerkin method and the RANS is computed using a classical finite-volume approach. The paper discusses the steps taken to create realistic inflow boundary conditions in terms of end wall boundary layer thickness and freestream turbulence intensity. This is achieved by tailoring the input distribution of total pressure and temperature, Reynolds stresses and turbulence length scale to a Fourier series based synthetic turbulence generator. With this procedure, excellent agreement with the experiment can be achieved in terms of blade loading at midspan and wake total pressure losses at midspan and over the channel height. Based on the validated setup, we focus on the discussion of secondary flow structures emerging due to the interaction of the incoming boundary layer and the turbine blade and compare the LES to two commonly used RANS models. Since we are able to create consistent setups for both LES and RANS, all discrepancies can be directly attributed to physical modelling problems. We show that both a linear eddy viscosity model and a differential Reynolds stress model coupled with a state-of-the-art correlation-based transition model fail, in this case, to predict the separation induced transition process around midspan. Moreover, their prediction of secondary flow losses leaves room for improvement as shown by a detailed discussion of turbulence kinetic energy and anisotropy fields. [ABSTRACT FROM AUTHOR]

The article investigates the feasibility of Large Eddy Simulation methods to accurately compute the flow around the Ahmed car body at 25 ∘ slant angle. The flow is computed at two different Reynolds numbers and with different turbulence modeling concepts using a large variety of grids. Issues associated with the accurate computation of the separation at the slant onset will be discussed in detail. [ABSTRACT FROM AUTHOR]

Copyright of Southern Energy Construction is the property of Southern Energy Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Southeast University / Dongnan Daxue Xuebao is the property of Journal of Southeast University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: The atmospheric boundary layer (ABL), whose total height is about 1–1.5 km, is composed of the atmospheric surface layer (ASL) and the Ekman layer, which typically account for the lower 10% and the upper 90% of the ABL, respectively. The wind veering angle in the Ekman layer can be between 10° and 30°, which may be an important influence factor for the wind‐resistant design of kilometer‐scale super‐tall buildings. Unfortunately, there is very little research on this issue so far due to the difficulty in simulations of veering wind in wind tunnels and computational fluid dynamics (CFD) simulation platforms. In this study, the simulations of non‐veering and veering wind fields are presented, and furthermore, the wind loads of kilometer‐scale super tall buildings with several typical configurations in veering wind fields are numerically investigated. Specifically, the large eddy simulations (LES) of unsteady flow around three buildings, namely, a square building, a tapered building (tapering ratio: 6.6%), and a 4‐layer setback building with the same height and the same aspect ratio of 9:1, are systematically performed for the cases of veering wind and non‐veering wind. The wind pressures and wind forces on these buildings are obtained and comprehensively analyzed. The differences in the wind loads among the building configurations are highlighted, and the mechanisms are discussed based on the time‐averaged and instantaneous flow fields. [ABSTRACT FROM AUTHOR]

We propose a model for magnetohydrodynamic flows at high Reynolds and magnetic Reynolds numbers. The system is written in the Elsässer variables so that the decoupling method of [C. Trenchea, Unconditional stability of a partitioned IMEX method for magnetohydrodynamic flows, Appl. Math. Lett.27 (2014), 97–100] can be used. This decoupling method is only first-order accurate, so the proposed model aims at improving the temporal accuracy (from first to second order), as well as reducing the modeling error of the existing turbulence model. This is done in the framework of the recently developed LES-C turbulence models [A. E. Labovsky, Approximate deconvolution with correction: A member of a new class of models for high Reynolds number flows, SIAM J. Numer. Anal.58 (2020), 5, 3068–3090]. We show the model to be unconditionally stable and numerically verify its superiority over its most natural competitor. [ABSTRACT FROM AUTHOR]

The effects of the coolant pulsation and the plasma aerodynamic actuation (PAA) on the film cooling are herein explored via large eddy simulations. The electrohydrodynamic force derived from the PAA was solved through the phenomenological plasma model. The Strouhal number of the sinusoidal coolant pulsation and the averaged pulsation blowing ratio were 0.25 and 1.0, respectively. Comprehensive analyses were carried out on the time-averaged flow fields, and the results reveal that the pulsed cooling jet might cause a deeper penetration into the crossflow, and this phenomenon could be remarkably mitigated by the downward force of the PAA. Comparing steady film cooling to pulsed film cooling revealed a modest 15.1% reduction in efficiency, while the application of the dielectric barrier discharge plasma actuator (DBDPA) substantially enhanced the pulsed film cooling efficiency by 42.1%. Moreover, the counter-rotating vortex pair (CRVP) was enlarged and lifted off from the wall more poorly due to the coolant pulsation, and the PAA weakened the detrimental lift-off effect and entrainment of the CRVP. Then, the spatial–temporal development of the coherent structures was figured out by the alterations in the centerline temperature, reflecting the formation of the intermittent coherent structures rather than hairpin vortices due to the coolant pulsation, and their size and upcast behaviors were reduced by the PAA; thus, the turbulent integration of the coolant with the crossflow was suppressed fundamentally. Finally, the three-dimensional streamlines confirmed that the coherent structure dynamic behaviors were significantly regulated by the PAA for alleviating the adverse influences of the coolant pulsation. In summary, the PAA can effectively improve the pulsed film cooling efficiency by controlling the spatial–temporal development of the dominant coherent structures. [ABSTRACT FROM AUTHOR]

In order to explore the blockage effect in the flow channel induced by the tip leakage of the semi-open centrifugal impeller, this paper uses the large eddy simulation to accurately calculate the flow field. Based on the blockage prediction model to investigate the blockage characteristics of three semi-open centrifugal impellers with tip clearance of 0.5, 1.0 and 1.5 mm under different flow conditions are studied. The research finds that there is a blockage peak in the impeller channel, and it is at plane 2 under the three tip clearances. After passing through plane 2, the blockage is greatly reduced, and there are small fluctuations in the back four sections. Through an analysis of the relative blockage at the trailing edge of the impeller under different tip clearances and different flow conditions, the study finds that the blockage at the trailing edge has the same change trend with the change of flow rate under different tip clearances. The relative blockage reaches the minimum at 1.0 Qd and the peak at 0.6 Qd. However, the relationship between blockage and tip clearance is not a single linear relationship at the same flow rate, and there is an optimal tip clearance to achieve the minimum blockage at the design point. At the same time, through the observation of the development of the leakage vortex, the study finds that the fragmentation and displacement of the leakage vortex will increase the blockage at the trailing edge of the blade. Through the analysis of the static pressure difference of the blade, the study finds that the operating flow has little effect on the blade load. However, the change of the tip clearance will greatly affect the blade load and the blockage at the trailing edge of the blade. [ABSTRACT FROM AUTHOR]

In response to growing environmental and ecological awareness, eco-friendly in-stream structures such as vanes have been implemented in different parts of the world to enhance stream conditions. FLUENT (ANSYS) was used to perform three-dimensional large eddy simulation to investigate the effect of the vanes permeability rate on flow characteristics. To evaluate the numerical model accuracy, numerical and experimental free surface profiles compared. It is observed that simulated free surface profiles agree reasonably well with measured values. The effect of different permeability rates is obvious in the flow characteristics such as depth-averaged velocity distribution, tip velocity variations, formation of the secondary flows in the flow field, turbulent kinetic energy, and mean kinetic energy contours. On average, maximum velocity values in the flow field is 1,54 times the approach velocity. Tip velocity decreases up to 30,6 % for the 70,0 % permeable vane. Maximum turbulent kinetic energy and mean kinetic energy for the 70,0 % permeable vane decrease up to 58,0 % and 43,3 %, respectively. Generally significant velocity and flow pattern variations around the impermeable vane can be attributed to the local effect of the vane structure and channel cross sectional constriction in comparison to the permeable vanes. [ABSTRACT FROM AUTHOR]

A numerical simulation is conducted to study the flow of a three-dimensional incompressible wall jet. The study aims to determine the jet structure and to compare the propagation mechanisms of turbulent and laminar wall jets. The numerical solution of the Navier–Stokes equations in the turbulent case is obtained using the wall-resolved large eddy simulation. The simulation results are compared to experimental data. [ABSTRACT FROM AUTHOR]

The air compression ratio in a modern aero engine has been significantly increased to enhance the engine's thermal efficiency, thereby leading to high-pressure combustion, with the combustor pressure exceeding the fuel's critical pressure (~23 atm for the aviation kerosene). In this work, large eddy simulations are conducted to investigate the effect of two air swirling injections on the flow dynamics and turbulent combustion of kerosene–air in a dual-swirl model combustor at a supercritical pressure of 4 MPa. The flamelet progress variable (FPV) model is applied to handle turbulent/chemistry interaction, and the extended corresponding states (ECS) method is adopted to evaluate thermophysical property variations. The results indicate that the inner air swirler controls flow and chemical reactions inside the injector, while the outer air swirler exerts a strong impact on the flow and flame characteristics in the combustor. A precessing vortex core (PVC) is generated by the inner swirling flow, and its frequency increases significantly as the inner air swirler angle varies from 25° to 40°. A modified Strouhal number is proposed for PVC frequency analyses, which reveal that the PVC frequency is influenced by the inner swirl number and the maximum axial velocity in the inner injector. The results obtained herein should help in developing a fundamental understanding of swirling flow and flame dynamics at high pressures. [ABSTRACT FROM AUTHOR]

The complex vortex structure compressor leads to the problem that the transition model is insufficient in predicting the flow instability of the compressor. In this paper, the rectangular cascade of compressor of different turning-angle conditions is taken as the object, and the transition characteristics on the end wall and the blade surface of the compressor cascade are in comparison by the method of large eddy simulation/LES. The effects of the horseshoe vortex and the separation bubble over the compressor cascade on the transition process are emphatically discussed. By analyzing characteristic parameters of the vortex structure, it is found that the separated transitional flow corresponds to multiple separations-and reattachments of the shedding vortex, and is affected by the cross-flow transition and the separate-transition. Finally, by discussing the instability of the separation line, reattachment line and the cross-flow inflection point of the separated transitional flow, it reveals that the transient disturbance caused by the vortex motion is an important reason affecting the prediction accuracy of the transition model. [ABSTRACT FROM AUTHOR]

As an essential component, the bleed system plays a critical role in supplying turbine cooling air, guaranteeing stage matching, pressurizing the cabin, and de-icing at the wing and engine inlet. However, the extraction of the bleeding air from the compressor causes the engine efficiency degradation and thrust deficit. Therefore, flow control based on bleed is conducted to compensate the bleed induced disadvantages. The influence of the circumferential bleeding slot location on the tip leakage vortex and passage vortex controlling in a compressor cascade with the tip clearance is numerically studied using large eddy simulation. Three bleed configurations and the smooth casing configuration are investigated. 17.11% loss reduction is obtained through bleeding at 10% cx upstream of the blade leading edge with a bleeding rate of 2.76%. The vortex structures and flow patterns are compared and analyzed to reveal the controlling mechanism. Subsequently, the axial vorticity and loss evolution is discussed, and the interaction between the primary flow and bleeding air is revealed. It's found that bleeding slot placed within the blade passage is exposed into a highly static pressure gradient, and this causes the bleeding air flows into and spills out the bleeding slot and leads to unnecessary loss. Moreover, the influence of large bleeding rate and inlet boundary layer is assessed. [ABSTRACT FROM AUTHOR]