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The structural performance of a Tensile Membrane Surface (TMS) as a lightweight structure is significantly influenced by environmental factors such as wind load. Only a few studies have been conducted to elucidate the effect of wind load on the internal forces, deformation, and stresses on a TMS, whereas the majority of contributions have concentrated on form-finding analyses and the structural performance of TMS structures. The most difficult part in the structural design of a TMS is the realistic estimation of wind load. In the current study, we performed fluid–structure interaction (FSI) analysis for an umbrella TMS considering practical uncertainties such as wind directions and flow effect for a group of structures. The lack of comprehensive standard codes is a great motivation for assessing the performance of TMSs under wind load. The Computational Fluid Dynamics (CFD) technique is widely employed to simulate the effects of airflow around buildings and special structures. The validation example was performed in an experimental test to verify the CFD simulation results by using both steady-state and transient wind simulations. The results of the aerodynamic simulation and FSI analysis include the wind pressure value, deformation, stress, and strain. This experiment was carried out on a single TMS with regard to various wind directions and a group of TMS umbrellas. The reduction value, especially for the uplift drag force component (Fz) of structural responses, was obtained for the group of structures. Furthermore, the impact of large deformation on the wind pressure coefficient was investigated, showing critical changes compared to the rigid approach, especially in suction zones. The results of the current CFD simulation were compared with the experimental test and show good agreement in terms of predicting the effect of air flow on TMS. [ABSTRACT FROM AUTHOR]

Piano Key Weir (PKW) is a non-linear weir with a small foundation footprint that allows large discharges through a narrow channel. The presence of overhangs classifies it into A, B, C, and D. For different PKW types, this study aims to assess the discharge, hydraulic characteristics (flow regimes, water surface profile, and nappes interference), and energy dispersion. This study employs the FLOW-3D software and validated by comparing experimental types A and D PKW with numerical simulations. Experimental and simulation results agreed well, with lower MAPE values for both types. After that, eight simulations for each PKW type were run, with headwater ratios (Ht/P) from 0.13 to 0.85 (Ht: total upstream head above crest, P: PKW height). Regarding discharge performance, type-B was superior to all other PKW types at lower heads (Ht/P ≤0.40) due to longer upstream overhangs. While at higher heads (Ht/P > 0.40), type-A became the highest PKW type. Since PKWs disperse energy more effectively than linear weirs, they acquire new performance as energy dissipators. Type-C had the highest energy dispersion rate, followed by type-A, type-D, and type-B. Finally, an empirical equation was provided to predict energy dispersion rates over PKW types as a function of discharge coefficient. [ABSTRACT FROM AUTHOR]

We investigate the need for the second correction step in the recently proposed LES-C models for fluid flows at high Reynolds numbers. These models use a predictor-corrector idea to enhance the efficiency of the existing Large Eddy Simulation models. Different three-step (one defect step, two corrections) LES-C models, based on the Leray- α , ADM and NS- ω LES models, are tested in three different situations. The new Leray- α -C2 model (C2 stands for two correction steps) is applied to the Navier–Stokes equations; the ADC2 is applied to the MagnetoHydroDynamic flow; and the NS- ω -C2 is used in the fluid-fluid interaction problem. We evaluate the effectiveness of the second correction step in all these settings, using qualitative and quantitative numerical tests. [ABSTRACT FROM AUTHOR]

In this paper, we obtain normal dispersive ℒ ℋ shock waves for ϕ ( 1) , ϕ ( 2) , ϕ ( 3) dam-break intensity by the nonlinear heat system. Then, we obtain super-fluid normal dispersive ℒ ℋ shock waves for ϕ ( 1) , ϕ ( 2) , ϕ ( 3) dam-break microfluidics. Finally, we illustrate thermonormal ℒ ℋ pressure of ϕ ( 1) , ϕ ( 2) , ϕ ( 3) wave energy with normal dam-break in shallow water. [ABSTRACT FROM AUTHOR]

This paper presents the uncertainty quantification and sensitivity analysis of the standard κ-ε turbulence model applied to the numerical prediction of the non-cavitating and cavitating flow around a 2D NACA66MOD hydrofoil. The turbulence model parameters are treated as epistemic uncertain variables, and the forward propagation of uncertainty is evaluated using the non-intrusive polynomial chaos approach. The required simulations are performed using a commercial CFD solver. The Sobol indices are used to rank the relative contribution of closure coefficients to the total uncertainty in the output quantities. For the considered case, the ranking of the model parameters is not influenced by the presence of the sheet cavity flow, while it varies with respect to the considered output quantity. [ABSTRACT FROM AUTHOR]

On the analysis of literary sources and working processes of a positive displacement pump we established that a hydrolic diode in positive displacement pumps improves their reliability and their most efficient application is in pumps in which the process of reverse flow into the working cavity into the discharge line is insignificant in time, for example, in spur rotary pumps. We established on comparing the results of a numerical experiment on the flow of a viscous incompressible fluid in a hydrolic diode, that the k-w model most accurately describes the fluid flow in a diaphragm hydrolic diode both quantitatively and qualitatively. The performed parametric analysis of the influence of the main parameters on the fluid flow in the hydrolic diode and the diodicity proved that the distance between the hydrolic diode plates should be within 35–40 mm; the angle of inclination of the plates to the body of the hydrolic diode should be 20°−30°; the number of pairs of plates should be within 7–9 pcs. [ABSTRACT FROM AUTHOR]

In this work, we propose a deep learning-based model for mapping between the data of the flow field of the propeller generated by the Reynolds-averaged Navier–Stokes (RANS) and those generated by Large Eddy Simulation (LES). The goal of establishing the mapping model is to generate LES data, which needs higher computing power requirements, with the help of RANS data. The model utilizes a deep learning method for computer vision to handle three-dimensional data generated by RANS and those by LES. Firstly, the data samples of the RANS flow field and those of the LES flow field are processed to obtain their corresponding three-dimensional image data, respectively. Secondly, the two kinds of field flow images are used as the training data for constructing a mapping model between RANS flow field images and the corresponding LES flow field images. The obtained mapping model thus can be used to predict the LES flow field images. Thirdly, the regression module is employed to regress the three-dimensional LES image point-by-point to the velocities at the points of the LES flow field, thereby ultimately achieving the generation of LES flow field data from RANS data. The experimental results show that by applying this method to RANS data and LES data of propeller flow fields, the overall error rate of LES flow field prediction by this method is 17.68% compared to actual flow field data, which verifies the effectiveness and accuracy of the proposed model in LES flow field prediction. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science 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.)

Parameters of turbulence model have rarely been changed to solve flow around ship hulls. Since these values are determined using relatively simple flows such as two-dimensional flat plate, there may be other parameter sets which are more suitable for resolving complex turbulent flow around ship hulls. Present study investigates suitable parameters of the k − ω SST model, one of the most popular turbulence models among ship flow simulations, throughout the data assimilation with ensemble Kalman filter aiming to improve computational accuracy of stern wake. Five parameters of k − ω SST model are first selected and are subjected to data assimilation using two-dimensional NACA4412 airfoil with moderate separation under 13.87 degrees of attack angle. Then, assimilated value " β 1 = 0.16 (originally 0.075)" which controls the production and destruction of ω is applied to solve four different blunt hull forms under towed condition. Bulk flow and available turbulence quantities on the propeller plane are subjected to validation. Consequently, the model parameter " β 1 = 0.16 (originally 0.075)" has been found to improve axial velocity distribution in model scale on the propeller plane in four different blunt hull forms maintaining the change of total resistance coefficient less than 0.8% difference compared to the original parameter. This research is of its first kind to bring the idea of parameter adaptation of turbulence model via data assimilation in the field of ship hydrodynamics. [ABSTRACT FROM AUTHOR]

Ducted propellers find widespread application across various vessels, such as fishing vessels, trawlers, and submarines, owing to their proven efficiency in propulsion systems. This paper explores the hydrodynamic impact of ducts on propeller performance through the application of a commercial Computational Fluid Dynamics (CFD) code. Additionally, an analysis of various turbulence models, including RNG k-ε, SST k-ω, and transition SST k-ω, was conducted to understand their effects on the calculated results. The propeller under consideration in this study possesses significant parameters: a diameter of 3.65 m, operating at 200 rpm, with an average pitch angle of 2.459 m and a boss ratio of 0.1730. The duct employed in the ducted propeller system features a NACA 4415 profile, chosen for its favorable hydrodynamic characteristics, making it well-suited for the propeller duct. The methodology involved the construction, meshing, and refinement of the geometry model for both the open water propeller and the ducted propeller system. Subsequently, the performance of these systems was analyzed using the RNG k-ε, SST k-ω, and transition SST k-ω RANS turbulence models. The study delves into the effects of the duct on the propeller's hydrodynamic features, as well as the influence of different turbulence models on the obtained results. The computed results presented encompass pressure distribution, hydrodynamic characteristics, and velocity profiles behind the propeller in various scenarios. The paper concludes with a comprehensive discussion of the effects of the duct on hydrodynamic features and the impact of different turbulence models on the results, providing valuable insights into the interplay between ducts and propeller performance. [ABSTRACT FROM AUTHOR]

Accurate turbulence modeling is essential for simulation studies of urban physics. In this study, the comprehensive atmospheric boundary layer (ABL) model involving a variable model coefficient and an additional turbulent dissipation source term was implemented using the open-source software OpenFOAM. Combined with consistent inlet wind profiles and rough wall functions of different turbulence variables based on the aerodynamic roughness, the model maintained the horizontal homogeneity well. Then, a hybrid approach was introduced to consider buildings immersed in ABL flows, enabling automatic transformation of the turbulence model between the region around the buildings and the free flow region away from any building. Finally, the effects of applying different model forms to the airflow field around buildings were evaluated in detail through three-dimensional building cases representing six urban prototypes based on three wind tunnel databases. Our findings indicated that all modified k–ε models perform well in reproducing the flow data of the CEDVAL and Architectural Institute of Japan (AIJ) experiments consisting of a single building, an array of buildings, and an isolated high-rise building. However, the modified k–ε model with an additional correction term performed poorly in the database of Niigata Institute of Technology and the case of complex terrain and urban building configurations, because the correction term inhibited the generation of turbulent kinetic energy. In addition, from the comparison between the experimental data of all cases, the model with the original formulation of the coefficient performed the best in terms of prediction accuracy. The root mean square errors of the normalized velocity were 0.1250, 0.0879, 0.1145, 0.1350, and 0.1492 in different cases, which proved the reliability of this turbulence model. [ABSTRACT FROM AUTHOR]

The correct prediction of the wind speed and turbulence levels over complex terrain is essential for accurately assessing wind turbine wake recovery, power production, safety, and wind farm design. In this paper, two modified RANS turbulence models are proposed, which are innovative variants of the conventional SST k-ω model and the linear Reynolds stress model (RSM) featuring optimized closure constants. Then, these two modified models and their origin models are applied to compare and analyze wind flows from a 3D hill wind tunnel experiment and two field measurements over typical complex terrain, including Askervein hill and Bolund island, with the aim of analyzing the sensitivity of wind flows to different RANS turbulence models. The study focuses on analyzing the effects of different turbulence models on the self-sustainability of wind speed and turbulent kinetic energy upstream of the computational domain and on the accuracy of wind flow prediction over complex terrain. The results show that our modified RSM model shows better agreement with the available experimental data on the upstream and leeward sides of all simulated hills. The wind speed on the leeward slope is particularly sensitive to the turbulence model, with a maximum difference in the relative root mean square error (RRMSE) that can reach 11% among the four models. The accuracy of the turbulent kinetic energy depends on the self-sustainability of the upstream turbulent kinetic energy and the predictive ability of the turbulence model for separated flows, and the maximum difference in the RRMSE of the four models can reach 47%. In addition, the advantages and disadvantages of the tested models are discussed to provide guidance for model selection during wind flow simulations in complex terrain. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering 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.)

The PRIUS program was established to generate an experimental database for the 6 × 4 and 12 × 6 rod bundle geometry. The database will be used to address the subchannel and CFD code analysis required for modeling and validation. This is necessary because Small Break Loss of Coolant Accident (SBLOCA) and Intermediate Break Loss of Coolant Accident (IBLOCA) present three-dimensional phenomena in the core due to the radial power profile, crossflow, and diffusion-dispersion. Therefore, specific experimental programs are required, especially during core reflooding, to investigate the large-scale three-dimensional effects. However, validating each sensitive model of the code separately in the presence of 3D effects is not possible due to the inability to implement instrumentation at high pressure and temperature steam-water flow conditions. The PRIUS test program uses a single-phase flow test to simulate a non-homogeneous velocity distribution and provide information on crossflow with radial mixing effects between subchannels. The CUPID code, which uses a macroscopic turbulence model, has been validated using the PRIUS-II experimental database. Existing macroscopic turbulence models were also validated for their prediction capabilities with different inlet flow conditions. However, the validation revealed significant errors in the shear region between subchannels. An improved macroscopic turbulence model showed promising results in predicting turbulence kinetic energy in porous media analysis.

Objectives: With the rapid development of electric vehicles (EVs), the maximum rotational speed of EV motors has reached up to 20 000 r/min. Precision polishing of gear surfaces after grinding has become a promising method for improving the noise, vibration, and harshness (NVH) performance of EVs. Abrasive Flow Machining (AFM) is one of the key technologies for efficiently polishing complex gear tooth surfaces. Fixture design plays a critical role in achieving process objectives, reducing surface ripple and roughness, and minimizing damage to the tooth surface accuracy. This article addresses the trade-off between selecting physical models and balancing the accuracy and computational cost of simulation results. It analyzes the impact of different simulation models on the results, providing guidance for AFM fixture design and offering practical experience for fixture optimization in AFM gear processing. Methods: Simulations are conducted using media with different viscosities, viscosity models, and flow models, within the simplest and most typical slit model. Fluid pressure distribution, velocity vectors, wall shear, and streamline distribution cloud mapsare analyzed to reflect machining uniformity. Based on the conclusions drawn from slit model simulations, the simplest Newtonian fluid—water—is selected as the medium for AFM gear shaft processing simulations. The focus is on the uniformity of streamline distribution in the machining area to optimize fixture design. Results: The analysis of slit model simulation results reveals that different physical models have varying impacts on the outcomes: (1) The selection of viscosity models decisively affects the pressure distribution of low-viscosity media. The type of viscosity and turbulence models has little impact on pressure distribution, but it significantly affects the velocity vector, wall shear, and streamline distribution within the abrasive cylinder. (2) For low-viscosity media: implementing a non-Newtonian fluid model has a significant impact on the pressure distribution. Different flow models show marked differences only in wall shear force distributions. Various viscosity models yield different cloud map distributions, but they produce numerically similar values. (3) For high-viscosity media: simulations with non-Newtonian and Newtonian fluid models show consistent results. However, different flow models greatly influence the results, while various viscosity models lead to changes in all simulation results, except for pressure distribution and streamlines within the slit. Despite these variations, the streamline distribution in the processing area remains largely unchanged. Based on the consistency of streamline distribution, fixture design optimization for the AFM gear shaft is carried out, successfully achieving the goal of eliminating gear "ghost frequencies". Conclusions: Despite variations in the physical models, the simulation results exhibit similar trends in distribution, enabling consistent streamline distribution in the processing area. For low-viscosity media, a non-Newtonian fluid viscosity model with laminar flow simulation can be used, and the selection of viscosity models can be simplified based on the rheological characteristics of the actual abrasive flow medium. For high-viscosity media, setting appropriate viscosity values and using laminar flow simulation with a Newtonian fluid model yields consistent pressure and streamline distribution in the processing area, similar to adding viscosity and turbulence models. The slit model simulation results and AFM gear shaft processing tests both demonstrate that streamline information derived from simple physical models can significantly assist in AFM fixture design. In cases where the physical properties of the abrasive flow medium are uncertain—especially in complex flow paths prone to divergence—using the simplest Newtonian fluid, such as water, with laminar flow simulation can provide a reasonable streamline distribution in the processing area. This approach aids in the analysis of processing uniformity, significantly reduces simulation difficulty and costs, and accelerates the fixture design cycle, ultimately enhancing optimization efficiency.

Steam ejectors are important energy-saving equipment for solar thermal energy storage; however, a numerical simulation research method has not been agreed upon. This study contributes to a comprehensive selection of turbulence models, near-wall treatments, geometrical modeling (2-D and 3-D), solvers, and models (condensation and ideal-gas) in the RANS equations approach for steam ejectors through validation with experiments globally and locally. The turbulence models studied are k-ε Standard, k-ε RNG, k-ε Realizable, k-ω Standard, k-ω SST, Transition SST, and linear Reynolds Stress. The near-wall treatments assessed are Standard Wall Functions, Non-equilibrium Wall Functions, and Enhanced Wall Treatment. The solvers compared are pressure-based and density-based solvers. The root causes of their distinctions in terms of simulation results, applicable conditions, convergence, and computational cost are explained and compared. The complex phenomena involving shock waves, choking, and vapor condensation captured by different models are discussed. The internal connections of their performance and flow phenomena are analyzed from the mechanism perspective. The originality of this study is that both condensation and 3-D asymmetric effects on the simulation results are considered. The results indicate that the k-ω SST non-equilibrium condensation model coupling the low-Re boundary conditions has the most accurate prediction results, best convergence, and fit for the widest range of working conditions. A 3-D asymmetric condensation model with a density-based solver is recommended for simulating steam ejectors accurately. [ABSTRACT FROM AUTHOR]

The aim of the study is to examine aerodynamic flow characteristics of a box girder and a twin-box girder have been investigated at Re = 20000. The methods based on k-ε and k-ω turbulence models have been compared. The minimum pressure has been observed on the lower surfaces for the box girder. Nevertheless, it has been provided for the upper surfaces of the twin-box girder. The highest value for turbulent kinetic energy has been obtained below the downstream fairing of the box girder. The same value has been attained in the slot. Lower values are weaker for the streamwise velocity components of the box girder. The lowest values have been seen in the gap of the twin-box girders and it behaved like a cavity. For cross-stream velocity components, maximum and minimum values depended on the rotational direction of the clusters. The wake has been enlarged perpendicular to flow for the twin-box girder, however, the wake shrunk due to the same effect. For the wake region, turbulence model and girder type have strongly influenced the velocity magnitude profiles. Drag coefficients are in good agreement with those previously reported. However, k-ω SST turbulence model has been suggested by a little margin. [ABSTRACT FROM AUTHOR]

The uncertainty of the turbulence/transition model is a problem with relatively high attention in the CFD area. Wall distance is an important physical parameter in turbulence/transition modeling, and its accuracy has a large effect on numerical simulation results. As most CFD solvers use the solving strategy to calculate the nearest distance to the wall based on mesh topology, this makes wall distance one important source of the uncertainty of the simulation results. To investigate the role of wall distance in turbulence/transition simulations, we have conducted simulations for various aerodynamic shapes, such as the plate with zero pressure gradient (ZPG), RAE2822 supercritical airfoil and ONERA M6 transonic wing. Further, the prediction abilities on turbulence/transition and shock wave phenomena of several physical models, including SA, SST and Wilcox-k-ω turbulence models as well as the γ-Reθt-SST transition model, are analyzed with different degrees of mesh orthogonality. The results imply that the numerical solution of wall distance in the boundary layer has a relatively large error when the mesh orthogonality is bad, having a large effect on the accuracy of the turbulence/transition model. In detail, the Wilcox-k-ω turbulence model is unaffected by mesh orthogonality; under the condition of mesh non-orthogonality, the SA model leads to a substantially larger friction drag and change in the location of shock wave; the SST model also leads to a larger friction drag under the condition of mesh non-orthogonality, whose effect is much less than that for SA model; and the γ-Reθt-SST model leads to a substantial upstream shift of transition location. [ABSTRACT FROM AUTHOR]

This paper simulates the temperature-dependent dynamic viscosity of the cutting fluid’s flow, thus analysing the approximated real behaviour in a simplified model. In order to take the heat transfer between the workpiece and the cutting fluid into account, the Finite Element Method (FEM) was bidirectionally coupled. A mathematical formula for determining the dynamic viscosity of the cutting fluid as a function of temperature was used for the temperature evolution. Simulations were performed using the standard k-ω-SST, k-ω-SST-SAS, and k-ω-SST-DES turbulence models for comparison. The results show that the influence of dynamic viscosity and temperature plays an important role and should therefore not be neglected in process simulations. For example, increasing the temperature from T = 25 °C to T = 150 °C reduced viscosity by 95%. The modelling approach presented here is suitable for future analysis simulations and can be applied not only to different drill geometries but also to numerous machining processes where dynamic viscosity plays an important role. [ABSTRACT FROM AUTHOR]

In this study, the effects of heat transfer on the impingement surface of a confined impinging array jet flow with 60° inclined secondary jets are investigated both experimentally and numerically. In the experimental section of the study, temperature distributions were obtained with a thermal camera among the middle axis of the impingement plate for 20000 and 30000 values of Reynolds number and 0.5, 1, 3 and 6 values of the aperture among plates. In the numerical section of the study, for the same Reynolds number and spacing values, bidimensional solutions were performed with the Kato Launder modified version of the Standard k-ε and Standard k-ω turbulence models and the calculated temperature distributions on the target impingement plate were compared with the experimental results. With measured temperature distributions, the effect of Reynolds number and aperture between plates on the Nusselt distributions on the target impingement plate is investigated. The Nusselt values on the surface of target impingement plate increase with increasing Reynolds number and decrease with increasing aperture between plates. The Nusselt number takes top point values at the impingement positions of the secondary jets on the impingement plate in the direction of their axes, and the positions of the top points shift to larger ±r/D values with increasing inter-plate spacing. It is observed that the Nusselt distributions calculated with both turbulence models are similar and the calculated results in the impingement region agree with the experimental results with a margin of error of 9 % and 11 % for the Standard k-ε and Standard k-ω turbulence models, respectively. [ABSTRACT FROM AUTHOR]

Fuel cell systems often utilize a hydrogen recirculation system to redirect and transport surplus hydrogen back to the anode, which enhances fuel consumption and boosts the efficiency of the fuel cell. Hydrogen recirculation pumps and ejectors are the most investigated systems. Ejectors are gaining recognition as an essential device in fuel cell systems. However, their application in hydrogen recirculation systems is often limited by a narrow operational range. Therefore, it is advantageous to compile the present condition of the study on various ejector shapes as well as configurations that can accommodate a broader operational range, along with the numerical simulations employed in these studies. This paper begins by examining the structure and operation of ejectors. It then compares and analyzes the latest advancements in research on ejector-based hydrogen recirculation systems with extended operating ranges and reviews the details of numerical simulations of ejectors, which are crucial for the development of innovative and efficient ejectors. This study provides key insights and recommendations for integrating hydrogen ejectors into the hydrogen cycle system of fuel cell engines. [ABSTRACT FROM AUTHOR]

The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine (VAWT) are investigated based on an in-house solver. This solver is developed on an in-house platform HRAPIF based on the finite volume method (FVM) with the elemental velocity vector transformation (EVVT) approach. The present solver adopts the density-based method with a low Mach preconditioning technique. The turbulence models are the Spalart-Allmaras (SA) model and the k-ω shear stress transport (SST) model. The inviscid spatial discretization schemes are the third-order monotone upstream-centered schemes for conservation laws (MUSCL) scheme and the fifth-order modified weighted essentially non-oscillatory (WENO-Z) scheme. The power coefficient, instantaneous torque of blades, blade wake, and turbine wake are compared and analyzed at different tip speed ratios. The extensive analysis reveals that the density-based method can be applied in VAWT numerical simulation; the SST models perform better than the SA models in power coefficient prediction; the rotation-curvature correction is not necessary and the third-order MUSCL is enough for power coefficient prediction, the high-order WENO-Z scheme can capture more flow field details, the rotation-curvature correction and high-order WENO-Z scheme reduce the length of the velocity deficit region in the turbine wake. [ABSTRACT FROM AUTHOR]

Copyright of Gazi Üniversitesi Fen Bilimleri Dergisi Part C: Tasarım ve Teknoloji is the property of Gazi University 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 Diamond & Abrasives Engineering is the property of Zhengzhou Research Institute for Abrasives & Grinding 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 Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering 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.)

The growing demand to reduce emissions of pollutants and CO2 from internal combustion engines has led to a critical need for the development of ultra-lean burn engines that can maintain combustion stability while mitigating the risk of knock. One of the most effective techniques is the pre-chamber spark-ignition (PCSI) system, where the primary combustion within the cylinder is initiated by high-energy reactive gas jets generated by pilot combustion in the pre-chamber. Due to the complex physical and chemical processes involved in PCSI systems, performing 3D CFD simulations is crucial for in-depth analysis and achieving optimal design parameters. Moreover, combining a detailed CFDs model with a calibrated 0D/1D model is expected to provide a wealth of new insights that are difficult to gather through experimental methods alone, making it an indispensable tool for improving the understanding and optimization of these advanced engine systems. In this context, numerous previous studies have utilized CFD models to optimize key design parameters, including the geometric configuration of the pre-chamber, and to study combustion characteristics under various operating conditions in PCSI engines. Recent studies indicate that several advanced models designed for conventional spark-ignition (SI) engines may not accurately predict performance under the demanding conditions of Turbulent Jet Ignition (TJI) systems, particularly when operating in lean mixtures and environments with strong turbulence–chemistry interactions. This review highlights the pivotal role of Computational Fluid Dynamics (CFDs) in optimizing the design of pre-chamber spark-ignition (PCSI) engines. It explores key case studies and examines both the advantages and challenges of utilizing CFDs, not only as a predictive tool but also as a critical component in the design process for improving PCSI engine performance. [ABSTRACT FROM AUTHOR]

This article establishes explicit non-asymptotic ergodic bounds in the renormalized Wasserstein–Kantorovich–Rubinstein (WKR) distance for a viscous energy shell lattice model of turbulence with random energy injection. The system under consideration is driven either by a Brownian motion, a symmetric α -stable Lévy process, a stationary Gaussian or α -stable Ornstein–Uhlenbeck process, or by a general Lévy process with second moments. The obtained non-asymptotic bounds establish asymptotically abrupt thermalization. The analysis is based on the explicit representation of the solution of the system in terms of convolutions of Bessel functions. [ABSTRACT FROM AUTHOR]

In the context of hypersonic flows, shock-wave/turbulent boundary-layer interactions (SWTBLIs) can lead to substantial aerodynamic heating. The commonly used Reynolds-averaged Navier–Stokes (RANS) method in engineering applications faces challenges in accurately predicting heat transfer in these conditions, as the assumptions made by Morkovin's assumption in the RANS method are not applicable in hypersonic SWTBLI flows. This article addresses these challenges by introducing a variable turbulent Prandtl number (P r t ) model for non-adiabatic walls, established through field inversion and symbolic regression (SR) techniques. The methodology begins with field inversion for an oblique SWTBLI case at Mach 5. The corrected field, denoted as β (x) , obtained from this inversion, is integrated with selected local flow characteristics to derive a corrected expression using SR. Following the necessary adjustments, this expression is incorporated into the RANS solver. Various cases with different wall cooling ratios, Mach numbers, and Reynolds numbers are chosen to assess the generalization ability of the variable P r t model. The outcomes demonstrate a substantial improvement in the model's ability to predict heat transfer in hypersonic SWTBLI flows without compromising the baseline model's performance in predicting the undisturbed boundary layer. The correction effect remains notably enhanced even in complex three-dimensional cases. • Corrected heat flux and skin friction by adjusting Reynolds stress and turbulent Prandtl number. • Developed a variable Prandtl number model using symbolic regression. • Analyzed physical mechanisms of the modified SST model for separated flow. analyzed. • Nine hypersonic SWTBLI flows showed significant improvements in calculations. [ABSTRACT FROM AUTHOR]

With the startup of the aero-engine, the ground vortex is formed between the ground and the engine intake. The ground vortex leads to total pressure and swirl distortion, which reduces the performance of the engine. The inhalation of the dust and debris through a ground vortex can erode the fan blade, block the seals and degrade turbine cooling performance. As the diameter of the modern fan blade becomes larger, the clearance between the intake lip and the ground surface is smaller, which enhances the strength of the ground vortex. Though considerable numerical studies have been conducted with the predictions of the ground vortex, it is noted that the accurate simulation of the ground vortex is still a tough task. This paper presents authors' simulation work of the ground vortex into an intake model with different crosswind speeds. This paper tackles the challenge with a parametric study to provide useful guidelines on how to obtain a good match with the experimental data. The influence of the mesh density, performance of different turbulence models and how the boundary layer thickness affects the prediction results are conducted and analysed. The detailed structure of the flow field with ground vortex is presented, which can shed light on the experimental observations. A number of suggestions are presented that can pave the road to the accurate flow field simulations with strong vorticities. [ABSTRACT FROM AUTHOR]

Modern large-scale gas turbines are equipped with high-pressure ratio compressors to increase engine work and its overall efficiency. Flow separation and energy losses are also two interrelated phenomenon associated with changes in compressor loading level and performance. This paper examines therefore the control of flow separation using a passive-control technique. An arced divergent-convergent slot grooved from the blade pressure side to its suction side was adopted to control flow separation, reducing the losses through a linear compressor cascade. The spanwise location of the slot was selected based on CFD simulations where the corner separation was predicted. The slot height in the spanwise direction was selected to be 8% of the blade height at the end-wall side. The present work was performed experimentally and numerically at an inlet Reynolds number, R ec = ρ V ∞ C / μ = 2.98 × 10 5 , covering a wide range of incidence angles from + 6 ∘ to - 6 ∘ . The experimental work was carried out using a linear cascade test section consisting of six NACA 65-009 blade profiles integrated into a low-speed wind tunnel. A five-hole pressure probe system was used to obtain main flow parameters. Numerically, four turbulence models, including Spalart–Allmaras (S–A) model, Realizable (R k-ε) model, Shear-Stress Transport (SST k-ω) model, and Reynolds Stress model (RSM) were tested to predict the velocity and pressure fields. Good agreement between the experimental measurements and the numerical results, which were obtained using the RSM turbulence model in terms of velocity profiles and total pressure downstream of blades. It was observed also that the use of the arced-slotted blades for positive incident angles was more effective in reducing the separation than the negative and zero incident angles, approaching a maximum value of 33% for 6° with enhanced blade loading reaching 17.6%. It is to be concluded that, the use of arced slotted blade improves the compressor performance specially for positive incident angles.Article Highlights: Compressor aerodynamic losses were reduced by groove arced diverged-converged slot. Numerical solution based on four turbulence models was proved experimentally. Results using Reynolds Stress turbulence Model were closest to experimental results. Slotted blades reduced losses by 33% for incident + 6° and improved loading by 17.6%. [ABSTRACT FROM AUTHOR]

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ABSTRACT Notwithstanding the abundance of different expository efforts by the engineers and scientists of the aerodynamic—transonic domain for the ever‐beseeched question of whether a supercar needs a rear spoiler or a rear wing, the query requires further exploration to come to any satisfactory conclusion. This state‐of‐the‐art bottleneck area is considered as the prime motivation of the paper as it seeks to investigate the aerodynamic phenomena of a notchback type supercar configuration with two different series of modifications—one with a rear spoiler attachment and the other one with a rear wing attached. A simplified Nissan Skyline GT34R CAD model is taken as the base ground vehicle for the computational study while the slant angles of both the rear wing and rear spoiler are changed within the range of 10° to 45°. RANS based k‐omega SST turbulence model is used to find the optimal slant angles for the corresponding rear wing and spoiler in terms of drag and lift coefficients, drag and lift force and rolling moment. The modified models with optimally slanted rear wing and rear spoiler along with the base configuration are inspected under different visualization techniques for understanding the aerodynamic phenomena. Contour and vector plots reveal that rear wing attached model has the maximum pressure drop along and over its body showing a sharp increase of 13.7% when compared with the rear spoiler attached model. Aftereffects show that both the turbulent intensity and Y+ wall shear stress is found to be most economical for the rear spoiler attached model, approximately 1.52% and 0.98% less than the base notchback model. Considering, overall aerodynamic performance of all the three proposed notchback type supercar configurations—the one with a rear spoiler attachment is found to be the most equipped one to integrate into future research.