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In this paper, the detached eddy simulation (DES) method is used to calculate the aerodynamic characteristics of NACA0015 airfoil by combining the Riemann approximate solution HLLC (Harten–Lax–van Leer Contact) with the high-order weighted essentially non-oscillatory (WENO) scheme and the weighted compact nonlinear scheme (WCNS), respectively. By comparing the calculation results of the two different numerical schemes with the wind tunnel test results, it is found that both numerical schemes can accurately calculate the aerodynamic parameters at small angles of attack. However, in the range of near-stall angle (in the range of 10–15°), the calculation results of various numerical schemes have a certain degree of deviation. The calculation results of the fifth-order WCNS and the fifth-order WENO scheme are closer to the experimental values. The fifth-order WCNS predicts the stall angle of attack more accurately than the fifth-order WENO scheme. The calculation accuracy of the fifth-order WCNS is better than that of the fifth-order WENO scheme under the post-stall condition (where the angle of attack is greater than 15°). By comparing the vorticity contours calculated by different numerical schemes, it is found that the numerical dissipation of the fifth-order accuracy is smaller than that of the third-order accuracy, and the vortex capture ability is stronger. WCNS captures the small vortex structure that the WENO scheme does not. [ABSTRACT FROM AUTHOR]

In recent years, it has been demonstrated for many two- and three-dimensional external and internal turbulent flows that the one-equation Wray-Agarwal turbulence model can compute the complex turbulent flow fields with high computational accuracy, excellent computational convergence and efficiency. In this paper, Wray-Agarwal (WA) turbulence model is employed as part of a detached eddy simulation (DES) method to predict the performance of a mixed-flow pump. By comparing the computations with the experimental results, the differences and similarities between the WA-DES model and the Shear Stress Transfer (SST) k-ω model in predicting the internal and external flow characteristics of the pump are analyzed. The results show that both the SST k-ω model and the WA-DES model can reasonably predict the performance of the pump between 0.6 Q and 1.2 Q, where Q is the design flow rate; however, they have their own merits and deficiencies in predicting head and efficiency of the pump at low and high flow rates. For the velocity field in the rotor-stator interaction region, the WA-DES model shows better prediction accuracy since it can accurately predict the large-scale recirculating vortex structure at the inlet of the guide vane. The SST k-ω model over-predicts the separated flow region, which leads to the emergence of a small vortex structure before the backflow region of the pump. Although the turbulent eddy viscosity predicted by the WA-DES model is higher than that of the SST k-ω model and there is small difference in the results for the scale of the tip leakage vortex (TLV) between the two models, the overall simulation results of the WA-DES model for the high turbulent viscosity region and the pressure increase in the impeller are consistent with the SST k-ω model results. The results of this paper demonstrate the potential of WA-DES model for prediction of flows in pumps. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology 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 Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) 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.)

In this paper, the detached eddy simulation (DES) method is used to calculate the aerodynamic characteristics of NACA0015 airfoil by combining the Riemann approximate solution HLLC (Harten–Lax–van Leer Contact) with the high-order weighted essentially non-oscillatory (WENO) scheme and the weighted compact nonlinear scheme (WCNS), respectively. By comparing the calculation results of the two different numerical schemes with the wind tunnel test results, it is found that both numerical schemes can accurately calculate the aerodynamic parameters at small angles of attack. However, in the range of near-stall angle (in the range of 10–15°), the calculation results of various numerical schemes have a certain degree of deviation. The calculation results of the fifth-order WCNS and the fifth-order WENO scheme are closer to the experimental values. The fifth-order WCNS predicts the stall angle of attack more accurately than the fifth-order WENO scheme. The calculation accuracy of the fifth-order WCNS is better than that of the fifth-order WENO scheme under the post-stall condition (where the angle of attack is greater than 15°). By comparing the vorticity contours calculated by different numerical schemes, it is found that the numerical dissipation of the fifth-order accuracy is smaller than that of the third-order accuracy, and the vortex capture ability is stronger. WCNS captures the small vortex structure that the WENO scheme does not.

Jet fuel-fired combustors in aero gas turbine engines have switched to lean burn to decrease nitric oxide emissions in recent years as a result of strict emission regulations. Lean operating conditions, however, exhibit a heightened sensitivity to thermoacoustic instabilities and such burners require careful consideration in design and operation. Similar to natural gas-fired combustors, they exhibit thermoacoustic instabilities, but the characteristics are more complex and less well-studied. This paper presents a numerical investigation of an airblast jet fuel swirl burner operating with preheated air at lean pressurized conditions. In order to understand the acoustic characteristics of the in-house designed burner (Magister UT burner), detached eddy simulations are performed at relevant aero engine conditions. Simulation results are then analyzed by means of our internally developed parallel modal analysis package, PARAMOUNT, to perform proper orthogonal decomposition (POD) on large datasets. The resulting modes are inspected to highlight flow features of interest and their associated acoustic frequencies at unforced conditions. Single frequency acoustic forcing is employed to study the acoustic response of the burner to perturbations at similar frequencies to its precessing vortex core. We show that parallel computation of POD modes is a viable tool to investigate the main flow features of swirl burners and is suitable for highlighting the important acoustic frequencies without the need to employ fully compressible computational fluid dynamics solvers. Additionally, the analysis method reveals the ways in which various flow structures correlate with each other and how external perturbations modify them. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology 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.)

Unsteady, viscous compressible flow is numerically simulated within first two stages of a low pressure turbine of a gas turbine engine under different clocking of its stator blades rows. Zonal DES turbulence modeling has been used for flow simulations. Time-dependent wake flow trajectory is modeled and visualized within the blades passages. All characteristics of the passage wake flow, including its V-shape motion, re-orientation, elongation, expansion, and stretching, are properly simulated. Unsteady flow field results together with those of general aerodynamic performance of the optimum and worst clocking cases are presented and compared with each other. Analyses of the flow simulation results showed that the optimum clocking of the blades rows occurs while the upstream wake flow impinges on the downstream stator blade leading edge region. Final results demonstrated that under the optimum clocking of the second stator, the inlet total pressure of the second rotor blades row and its output power increase by 0.1% and 0.336%, respectively. Consequently, efficiency of the second stage increases by 0.35%. In addition, total output power of the whole two stages increases by 0.237%. [ABSTRACT FROM AUTHOR]

Due to the distinctive structure of the test section, the open jet wind tunnel generates low-frequency pressure fluctuations (LFFs) within the range of typical wind speeds. These fluctuations significantly compromise the quality of the flow field in the test section. The evolution of the flow structure and vortex is analysed through the improved delayed detached eddy simulations (IDDES). The LFFs and the control mechanism in the open jet wind tunnel of Jilin University are then studied. The interaction between the large-scale vortex shedding at the nozzle exit and the collector forms the edge feedback, which is the main reason for the pressure fluctuation. According to the feedback mechanism, the LFFs are suppressed using the throat gap and by improving the collector shapes. The results show that the increase of the throat gap length at the collector can significantly alleviate the pressure accumulation inside the collector. The change of the collector shapes can control the impact area and time of the incoming flow, or produce permanent vortex structure to affect the impact shape of the vortex and the flow field at the collector, which allows to control the LFFs. This study lays a solid foundation for further comprehension of the aerodynamic characteristics of the open jet wind tunnels.

Due to the distinctive structure of the test section, the open jet wind tunnel generates low-frequency pressure fluctuations (LFFs) within the range of typical wind speeds. These fluctuations significantly compromise the quality of the flow field in the test section. The evolution of the flow structure and vortex is analysed through the improved delayed detached eddy simulations (IDDES). The LFFs and the control mechanism in the open jet wind tunnel of Jilin University are then studied. The interaction between the large-scale vortex shedding at the nozzle exit and the collector forms the edge feedback, which is the main reason for the pressure fluctuation. According to the feedback mechanism, the LFFs are suppressed using the throat gap and by improving the collector shapes. The results show that the increase of the throat gap length at the collector can significantly alleviate the pressure accumulation inside the collector. The change of the collector shapes can control the impact area and time of the incoming flow, or produce permanent vortex structure to affect the impact shape of the vortex and the flow field at the collector, which allows to control the LFFs. This study lays a solid foundation for further comprehension of the aerodynamic characteristics of the open jet wind tunnels. [ABSTRACT FROM AUTHOR]

The use of adaptive meshing strategies to perform cost-effective transient simulations of spray drying processes is evaluated. These simulations are often computationally expensive, given the large differences between the characteristic times of the central jet and those of the unsteady flow developed at its periphery. Managing the computational cost through the control of the grid resolution by regions is inadequate in many of these applications since the grid resolution requirements change dynamically within the domain. These conditions are related to the unsteady nature of the flow in both the central jet and the flow recirculation zones. Therefore, the application of adaptive mesh refinement (AMR) strategies is recommended. In this paper, general AMR criteria based on relative errors are evaluated by testing three mesh adaptation criteria: velocity gradient, pressure gradient, and vorticity. This evaluation is performed using a low-cost turbulence model with eddy resolution (DDES) in two different types of drying chambers, in which experimental measurements are available. The use of AMR exerts appreciable effects on decreasing computational costs and contributes to the capture of large eddies in critical regions. The present approach provides an appropriate balance between solution accuracy and computational cost. By using a correct AMR configuration, it is possible to obtain results similar to those obtained on a fixed grid but reducing the computational costs by 3 to 5 times. [ABSTRACT FROM AUTHOR]

This study aims to derive valuable insights for utilizing computational fluid dynamics (CFD) based on reynolds-averaged navier–stokes (RANS) and detached eddy simulation (DES) turbulence models (TMs) to analyze a specific radial ejector configuration known as the variable geometry radial ejector (VGRE). The VGRE features the primary nozzle and ejector duct plates with adjustable disk-like surfaces, allowing for changes in the nozzle and ejector throat areas within a single ejector. Extensive numerical investigations of the VGRE are conducted by systematically validating CFD models with experimental datasets and subsequently using the most appropriate TM to design a new radial ejector. The study reveals that the DES SST k-ω turbulence model achieves the closest agreement with experimental data, with an average entrainment ratio (ω) discrepancy of only 5 %. However, there are challenges in accurately predicting the critical compression ratio (rc*), especially under varying conditions. Based on the CFD results, the original VGRE exhibited ω values ranging from 0.16 to 0.61, rc* values between 1.5 and 3.1, and ejector efficiency (η) values between 7 % and 17 % at expansion ratio (re) values ranging from 89 to 150 for different nozzle throat separations (d) and different duct throat separations (D). Furthermore, this study presents a comprehensive investigation into predicting and optimizing ω, rc*, and η parameters using a multi-output gaussian process regression (GPR) model and a marine predators algorithm (MPA) approach. The multi-output GPR model was constructed to predict the relationships between boundary conditions (primary pressure (Pprimary) and secondary pressure (Psecondary)), geometric parameters (d and D), and the response variables (ω, rc*, and η). The model evaluation employed a 5-fold cross-validation technique to assess predictive performance, demonstrating strong predictive accuracy with low root mean square error (RMSE) and high coefficient of determination (R2) values. The optimization results revealed that the highest achieved values were ω = 0.303, rc* = 2.678, and η = 0.156, corresponding to specific parameter settings (Pprimary = 160 kPa, Psecondary = 1.8 kPa, d = 0.6 mm, and D = 2.3 mm). This study demonstrates the effectiveness of the multi-output GPR model for accurate prediction and the multi-objective MPA optimization approach for identifying optimal input parameters to maximize entrainment ratio, critical compression ratio, and ejector efficiency in fluid dynamics systems.

To explore the fluid-structure interaction (FSI) effect on the wind-induced response of high-rise building, the CAARC (Commonwealth advisory aeronautical research council) high-rise building model was taken as the research object. An aeroelastic model was established based on the physical characteristics of the CAARC model. A new turbulence generation method discretizing and synthesizing random flow generation(DSRFG) was used to generate inlet turbulence. The one-way FSI and two-way FSI simulation technique was carried out by using the detached eddy simulation(DES) method. The results were compared with the wind tunnel test. It shows that the aeroelastic characteristics of the structure are consistent, and the DES method has strong applicability and accuracy in simulating the unsteady wind field. The one-way FSI and two-way FSI simulation results have great differences in flow field and windinduced response. In terms of flow field, the two-way FSI has a wider wake area near the structure than the one-way FSI. In addition to the drag coefficient, the response of the two-way FSI has a decreases trend when compared with that of the one-way FSI, and the along wind direction of the structure is also more susceptible to the fluid-structure coupling effect. On a low structural damping level, the aerodynamic damping caused by FSI effect has a great influence on the structural response, the FSI effect of high-rise buildings cannot be ignored. [ABSTRACT FROM AUTHOR]

The flow parameters through complex-type bridge piers configured in various geometries were explored and compared in this work using dye visualisation and computational fluid dynamics (CFD) methods. The Detached Eddy Simulation (DES) technique based on the SST k omega model has been chosen to investigate the flow characteristics around complex bridge piers, and time-averaged normalised mean streamwise velocity, time-averaged normalised mean cross-stream velocity, time-averaged normalised mean pressure, time-averaged normalised mean Reynolds shear stress, time-averaged normalised mean y vorticity, time-averaged normalised mean z vorticity, and drag coefficient have been selected as parameters for this study. According to the study's findings, when the time-averaged normalised mean streamwise velocity component of all complex bridge piers was examined, the pile sections had the highest values. Drag coefficients have been sorted from low to high when comparing complex bridge piers in all geometries such as elliptical, circular, rectangular, and square. Article Highlights Flow characteristics around complex bridge piers Dye visualisation experiments and CFD method with DES based on the SST k omega model Drag Coefficients of complex bridge piers [ABSTRACT FROM AUTHOR]

Cavitation and cavitation erosion often occur and seriously threaten the safe and stable operation of hydraulic machinery. However, during the operation of hydraulic machinery, the cavitation flow field is often difficult to contact andmeasure, and the shedding and development characteristics of cavitation floware unknown. This paper uses theDetached Eddy Simulation (DES) turbulence model and Zwart-Gerber-Belamri (ZGB) cavitationmodel to conduct numerical research on the cavitation flow of a twisted hydrofoil and verifies the effectiveness of numerical simulation by comparing it with experimental results. Then, based on the fractal dimension method, the number and fractal dimension of themain cavitation clusters in two different views are analyzed. The research results show that with the continuous flow of fluid, the cavitation at the tail of the hydrofoil periodically falls off, and the number of cavitation bubbles shows a strong randomness between 1 and 2. The fractal dimensionmethod calculates that the frequency of cavitation bubbles falling off is 30 Hz. The fractal dimension of cavitation also fluctuates periodically. The fractal dimension of cavitation in the side view fluctuates between 1.30-1.38, and the fractal dimension of cavitation in the top view fluctuates between 1.31-1.42. The fractal dimension of the cavitation is closely related to the size and shape of the cavitation. By analyzing the relationship between the cavitation development process and the fractal dimension in the side view, we found the relationship between the development of cavitation in a cycle and the change of fractal dimension, which is of great significance to understanding the characteristics of cavitation flow through the image of the cavitation flow field. [ABSTRACT FROM AUTHOR]

• Drag/lift fluctuation dominate in-line/transverse noise propagation respectively. • Noise is suppressed for range of cylinder oscillation frequencies in turbulent flows. • Loading and thickness noise exhibit discrepancy. • Sound pressure more sensitive to oscillations of downstream than upstream cylinder. • Oscillation direction affects noise in contrast form for single and tandem units. The noise generated by a three-dimensional turbulent wake behind an oscillating single or tandem cylinder(s) is studied using detached eddy simulation and the Ffowcs Williams-Hawkings (FW-H) method. This hybrid methodology is validated using some experimental data of a turbulent flow past a single or tandem stationary cylinder(s) and some numerical data (obtained from a direct numerical simulation) of a laminar flow past tandem oscillating cylinders. For an oscillating cylinder at a fixed Reynolds number R e = 120 , 000 , the sound energy is suppressed compared to that of a stationary cylinder provided the value of oscillation frequency approaches 57% of the original vortex-shedding frequency of the stationary cylinder. This noise reduction arises from the structural oscillations suppressing the noise generated by the vortex shedding from the stationary cylinder—the additional source of noise stemming from the structural oscillations is too small to compensate for the mechanism responsible for the noise suppression. The noise generated by the cylinder motion includes contributions from the loading and thickness noise, whereas the noise generated by vortex shedding from the stationary cylinder only includes the loading noise. The flow past tandem stationary cylinders exhibits a larger number of spectral peaks in the sound pressure power spectrum and the peaks occur at a lower frequency compared to the flow past a single cylinder. The drag force fluctuations result in the propagation of the sound pressure in the in-line direction, whereas the lift force fluctuations result in the propagation of the sound pressure in the transverse direction. Five different scenarios of stationary and/or oscillating tandem cylinders are studied. The second and third invariants of the velocity gradient tensor are used to visualize the distinct vortex structures in the wake for the five different scenarios of tandem cylinders. A single cylinder oscillating in the transverse direction exhibits a larger sound pressure level (SPL) than the streamwise oscillation of the same cylinder. In contrast, the streamwise (in-line) oscillation of one or the other cylinder in a tandem array results in a larger SPL than the transverse oscillation of one or the other cylinder. Finally, the SPL is more sensitive to the oscillations of the rear (downstream) cylinder than the front (upstream) cylinder. [ABSTRACT FROM AUTHOR]

An assessment of a hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation (HRLES) approach for CL,max prediction is presented for the NASA High-Lift Common Research Model (CRM-HL). Both free-air and wind tunnel configurations of the CRM-HL are investigated, and the results are compared to the QinetiQ wind tunnel experiments and two other numerical approaches: RANS and wall-modeled LES (WMLES). For the free-air configuration, HRLES is shown to address some of the known shortcomings with RANS and prevent inboard and outboard flow separation particularly in the region of CL,max and poststall. To achieve these improvements over RANS, LES-appropriate grids and numerical discretizations are required. It was also found that, when applying HRLES to a RANS best practice grid and numerics, the HRLES method significantly underperformed RANS. For the in-tunnel configuration, HRLES showed good agreement with the loads, surface pressure, and oil-flow photographs obtained in the experiment. HRLES was able to improve upon the RANS simulations, which showed a sharp loss of lift at the two highest angles of attack due to large-scale inboard and outboard separation on the wing, by correctly predicting the corner flow separation and showing remarkably close agreement in the flow topologies with the experiment. [ABSTRACT FROM AUTHOR]

The ‘Bajo Grande’ Wastewater Treatment Plant has a design capacity of 2.78 m3/s, and discharges into the Suquia River (Córdoba, Argentina). The river has an average flow rate of 10 m3/s, with lower values during the summer. Currently, the treatment plant does not have an accurate discharge-measurement system prior to the discharge into the river, which makes it difficult to evaluate the dosing of the disinfection treatment. The outflow rate is measured in a straight flume. However, at the inlet section of the flume, a 180° sharp bend induces a complex turbulent flow with instabilities and low-frequency velocity fluctuations which are not appropriate for flow quantification. In this type of flow, most of the in situ flow discharge-measurement systems have great uncertainty. Therefore, in situ flow measurements with an Acoustic Doppler Current Profiler, Large-Scale Particle-Tracking Velocimetry techniques and a prototype-scale Detached Eddy Simulation model were combined to obtain a detailed characterization of the turbulent flow. The results provide flow rates, fields of mean flow velocity, temporal evolution, and characteristic parameters of the turbulence. This allowed a better understanding of the effects of turbulence and flow instabilities. The results provide a basis to validate numerical models used in the hydraulics design of contact chambers to improve the disinfection process. HIGHLIGHTS The work focuses on the study of a complex turbulent flow, with flow instabilities and low-frequency fluctuations.; An Acoustic Doppler Current Profiler and Large-scale Particle Image Velocimetry (LS-PIV) were applied to characterize turbulent flow in a prototype-scale contact chamber.; DES simulation was used to detailed characterization of a complex turbulent flow; particularly, the spatial and temporal evolution.;

In view of the importance of understanding and predicting the effects of wind on wide-span membranes and inflatable structures, a complementary experimental-numerical campaign was conducted to demonstrate the physical importance of numerical simulations in this field and to discuss relevant modeling aspects. This work aims, on the one hand, to examine the effects of some main CFD modeling decisions, such as mesh resolution, turbulence modeling, wall functions, etc., on the accuracy of simulation results. On the other hand, to compare the two most popular CFD numerical technologies (Finite Volumes and Finite Elements Methods), using the open-source frameworks OpenFOAM and Kratos Multiphysics, respectively. This parametric study and cross-validation will contribute to the ultimate goal of obtaining practical and reliable predictive numerical simulations in the field of wind engineering. This paper discusses the numerical modeling approaches of the first and fundamental step of a systematic chain of test cases, performed experimentally. It focuses on the case where a constant uniform flow and a rigid inflatable membrane structure are considered. Further extensions will include ABL flow scenarios and fluid-structure interaction. [ABSTRACT FROM AUTHOR]

Numerical simulations were carried out to explore the flow characters and swirl distortion features of RAE M2129 S-Duct inlet using detached eddy simulation. Three freestream conditions at Mach 0.21, at angle of attack between 0 and 12 deg and at angle of sideslip between 0 and 12 deg are simulated. Results suggest that the time-averaged flow features and the aerodynamic performance of the S-Duct inlet for three freestream conditions are similar to each other; meanwhile, the time-averaged swirl distortion descriptors are also close to each other. Nevertheless, the instantaneous small-scale turbulent structures primarily induced by the freestream angle of attack lead to the generation of more strong vortices at the inlet exit plane between inlet center cone and the stbd wall, which results in larger fluctuating swirl distortions. Furthermore, the fluctuating velocity in transverse direction is more positively correlated with circumferential velocity, while the fluctuating velocity in longitude direction is more negatively correlated with circumferential velocity. [ABSTRACT FROM AUTHOR]

The evolution of cavitation flow involves intense transient characteristics and complex multi-scale motions, significantly increasing the difficulty and computational cost of solving in separation zones. This study proposes an Improved Detached Eddy Simulation (IDES) method, based on a single-equation eddy-viscosity model, aimed at enhancing the resolution of small-scale cavitation flows. By incorporating the broad-spectrum von Karman scale concept, the method effectively improves the resolution capability for small-scale flows in separated zones. The performance of the IDES model was validated through three computational cases, and the main conclusions are as follows: The results of the triangular cylinder flows show that the IDES model demonstrates a resolution capability for large-scale turbulence comparable to the Large Eddy Simulation (LES) model. The orifice flow results indicate that activating the LES method with insufficient grid resolution is highly discouraged, whereas the IDES model performs more robustly under such conditions. For hydrofoil flows, the IDES model more accurately captures the temporal evolution of cavitation, avoiding the premature cavity shedding predicted by LES under coarse grid conditions. The decomposition results of the vorticity transport equation show that both the dilatation term and viscous term are significant contributors in the vorticity transport process, with their average contributions to vorticity reaching 49.25% and 39.99%, respectively. Vortices can be considered the primary controllers of cavitation dynamics, while the dilatation term and viscous term can be regarded as the main controllers of vorticity. Overall, the energy compensation mechanism of the IDES model, based on local flow information, gives it unique advantages in handling small-scale turbulence and cavitation phenomena, providing both high computational efficiency and accuracy. • This paper developed a hybrid RANS-LES model that improves turbulence resolution in small-scale cavitation flows. • The IDES method models the stress compensated for turbulence resolution based on local flow information. • The IDES model has the potential to be an economically efficient solution for resolving cavitation flows. [ABSTRACT FROM AUTHOR]

The use of adaptive meshing strategies to perform cost-effective transient simulations of spray drying processes is evaluated. These simulations are often computationally expensive, given the large differences between the characteristic times of the central jet and those of the unsteady flow developed at its periphery. Managing the computational cost through the control of the grid resolution by regions is inadequate in many of these applications since the grid resolution requirements change dynamically within the domain. These conditions are related to the unsteady nature of the flow in both the central jet and the flow recirculation zones. Therefore, the application of adaptive mesh refinement (AMR) strategies is recommended. In this paper, general AMR criteria based on relative errors are evaluated by testing three mesh adaptation criteria: velocity gradient, pressure gradient, and vorticity. This evaluation is performed using a low-cost turbulence model with eddy resolution (DDES) in two different types of drying chambers, in which experimental measurements are available. The use of AMR exerts appreciable effects on decreasing computational costs and contributes to the capture of large eddies in critical regions. The present approach provides an appropriate balance between solution accuracy and computational cost. By using a correct AMR configuration, it is possible to obtain results similar to those obtained on a fixed grid but reducing the computational costs by 3 to 5 times.

A numerical study is conducted to determine the hydrodynamic coupling characteristics of a contra-rotating azimuth propulsor (CRAP) in open-water conditions. The detached-eddy simulation (DES) method is utilized to run simulations. A grid verification is conducted and the numerical results are validated based on a puller-type podded propeller. The hydrodynamic forces (i.e., thrusts and torques) are in accordance with the experimental data. The validated numerical method is utilized for subsequent CRAP simulations. The hydrodynamic performance and hydrodynamic coupling characteristics of CRAP are quantitatively analyzed according to forward propeller (FP), rear propeller (RP), and pod unit (PU) indicators with special focus on the hydrodynamic forces and the corresponding unsteadiness. PU appears to have essentially the same effect on the hydrodynamic performance of FP and RP. RP has a weak effect on the hydrodynamic performance of FP, while FP intensely affects that of RP. In general, the CRAP unsteadiness is dominated by RP, especially under heavy loading conditions.

The flow fields around vehicle drag reduction devices are three-dimensional, complicated, and unsteady. Meanwhile, the small scale of the drag reduction device brings more challenges to the simulation. An Improved Delayed Detached Eddy Simulation (IDDES) was applied to study the effect of two types of drag reduction device. First, the flow field of an Ahmed body at a 25° slant was simulated in detail using IDDES and verified by experiment data. Afterwards, the flow field structures of adding-on vortex generators (VGs) and riblets on the rear and slant surface of the Ahmed body were studied. The simulation results of the velocity, pressure and vortex structure on the controlled case are presented by comparing with the baseline model to illustrate the drag reduction mechanism. The two drag-reduction devices had different flow mechanisms and significantly affected the development of the separation vortex near the rear and slanted surface. A maximum drag reduction of 6.21% could be achieved using VGs on the rear surface. Finally, four combinations of those two devices were investigated. The results demonstrated that suitable combinations can further decrease the aerodynamic drag, and an 8.62% drag reduction is achieved.

In this study, a novel fluidic jet actuator is designed to control flow separation on a NACA0015 airfoil at various angles of attack. The U-shaped jet actuator has two rectangular slots implemented near the leading edge of the airfoil. It is driven by a piston mechanism and operates at three excitation frequencies. Depending on the motion of the mechanism, a synchronized jet flow is generated by blowing and suction at the dual exits of the actuator slots. The experimental studies are carried out in a subsonic wind tunnel. The unsteady 2D Computational Fluid Dynamics simulations are performed by Detached Eddy Simulation with the SST k-ω turbulence model where measured jet velocities at the exits of the actuator slots are imposed as boundary conditions to mimic motion of the piston. The results at the on-mode and off-mode of the actuator are evaluated in terms of surface pressure coefficient distributions on the airfoil and averaged aerodynamic force coefficients. At low angles of attack, there is an adequate match between numerical and experimental results for the base flow without any control. At higher angles of attack, flow separation becomes considerably dominant and stall prevention by active flow control is detected especially at high excitation frequencies‎.

Axisymmetric simulations of a liquid rocket engine are performed using adelayed detached-eddy-simulation (DDES) turbulence model with the CompressibleFlamelet Progress Variable (CFPV) combustion model. Three different pressureinstability domains are simulated: completely unstable, semi-stable, and fullystable. The different instability domains are found by varying the combustionchamber and oxidizer post length. Laminar flamelet solutions with a detailedchemical mechanism are examined. The $\beta$ Probability Density Function (PDF)for the mixture fraction and Dirac $\delta$ PDF for both the pressure and theprogress variable are used. A coupling mechanism between the Heat Release Rate(HRR) and the pressure in an unstable cycle is demonstrated. Local extinctionand reignition is investigated for all the instability domains using the fullS-curve approach. A monotonic decrease in the amount of local extinctions andreignitions occurs when pressure oscillation amplitude becomes smaller. Theflame index is used to distinguish between the premixed and non-premixedburning mode in different stability domains. An additional simulation of theunstable pressure oscillation case using only the stable flamelet burningbranch of the S-curve is performed. Better agreement with experiments in termsof pressure oscillation amplitude is found when the full S-curve is used.

Multi-element wing tips based on bird wings appear attractive in soaring flight, where a minimal sink velocity is the design goal. The present study aims to reproduce the soaring flight observed from white storks (ciconia ciconia) in a biomimetic computational model in order to visualize and investigate the flow around and through the wing tip cascade. RANS and hybrid RANS–LES computations have been performed allowing access to all features of the flow field. The resulting properties in soaring flight have been compared to measured data of free flying birds from the literature to qualify the results of the re-engineered wing. Further, the flow field has been analyzed in detail to understand the underlying flow physics and to point out relevant phenomena such as a system of vortices associated with the wing and tip design which contributes to the observed aerodynamic properties. [ABSTRACT FROM AUTHOR]

A numerical investigation of the rapid turbulent filtration combustion within a packed pebble bed is conducted at a fixed superficial velocity of 0.5 m/s, equivalence ratio of 1.0 (methane/air) under two background pressures of 1.0 and 0.5 MPa. Turbulence is modeled with the detached eddy simulation (DES) method. The interaction between turbulence and chemical reaction is considered through the fast reaction method, i.e., burning velocity model (BVM). To validate the DES method, the relative turbulence intensities in a 3D staggered cylinders are verified previously which are in excellent agreement with the experimental data (no reaction). With the confidence in the DES method, the turbulent combustion characteristics in a 3D packed pebble bed are studied in detail, including pressure fluctuation, spatial inhomogeneities of velocity and temperature fields, and evolution of the flame surface. Numerical results show that a strong pressure fluctuation arises after ignition due to thermal expansion contributing significantly to the velocity and temperature fluctuations for the case of 1.0 MPa, whereas it is relatively moderate for the case of 0.5 MPa. Though the evolution of the flame surface both can be divided into two stages for the two cases, i.e., initial-rapid spreading stage, and stable propagating stage, there is a slight difference between them. Specifically, it closely resembles to an atomic blast for the former, while it is similar to a volcanic eruption for the later. Undergoing this stage, about 20 ms, the wrinkle and fragmented flames or flamelets creep over the pebbles through the thin layers close to the walls. Statistical stability is identified in the process of flame propagating upstream. Turbulent flame speeds obtained in this study agree well with the experimental data, especially for the case of 1.0 MPa. [ABSTRACT FROM AUTHOR]

This paper presents a novel theoretical and computational methodology for the generation of an onset turbulent field with prescribed properties in the numerical simulation of an arbitrary viscous flow. The methodology is based on the definition of a suitable distribution of volume force terms in the right-hand side of the Navier–Stokes equations. The distribution is represented by harmonic functions that are randomly variable in time and space. The intensity of the distribution is controlled by a simple PID strategy in order to obtain that the generated turbulent flow matches a prescribed turbulence intensity. A further condition is that a homogeneous isotropic flow is established downstream of the region where volume force terms are imposed. Although it is general, the proposed methodology is primarily intended for the computational modelling of hydrokinetic turbines in turbulent flows representative of tidal or riverine installations. A first numerical application is presented by considering the injection of homogeneous and isotropic turbulence with 16% intensity into a uniform unbounded flow. The analysis of statistical properties as auto-correlation, power spectral density, probability density functions, demonstrates that the generated flow tends to achieve satisfactory levels of stationarity and isotropy, whereas the simple control strategy used determines underestimated turbulent intensity levels. [ABSTRACT FROM AUTHOR]

Baraj yıkılmasının meydana gelmesi durumunda özellikle barajın mansap bölgesinde oluşacak mal ve can kaybının en aza indirgenmesi ve barajın planlama aşamasında gerekli önlemlerin alınması için, baraj yıkılmasının sayısal modelleme teknikleriyle analiz edilmesi önemlidir. Ayrıca, mevcut barajların yayılım dalgasının mansap bölgesine olan etkisinin farklı senaryolarla analizi de bu yöntemler kullanılarak gerçekleştirilebilmektedir. Bu çalışmada, baraj mansabında herhangi bir yapı veya akım bulunmaması durumunda (kuru yatak) gerçekleşen baraj yıkılmasının sayısal modellemesi, sonlu hacimler yöntemiyle ANSYS- Fluent paket programı kullanılarak yapılmıştır. Sayısal modellemelerde baraj yıkılması yayılım dalgası akımını idare eden temel denklemlerin çözümünde, Re-normalization Grup k-ɛ (RNG), Kayma Gerilmesi Taşınım (Shear Stress Transport -SST) ve Ayrılmış Girdap Benzetim (Detached Eddy Simulation- DES) modelleri, su hava ara kesitinin belirlenmesinde ise akışkan hacimleri yöntemi (Volume of Fluid-VOF) kullanılmıştır. Farklı zamanlarda elde edilen deneysel ve sayısal su yüzü profillerinin karşılaştırılmasından, DES modelinin kullanılan diğer modellere kıyasla nispeten daha başarılı olduğu belirlenmiştir. Çalışma sonucunda, baraj yıkılması durumunda barajların mansap bölgesinin güvenlik önlemlerinin ve risk sınırlarının belirlenmesinde, sayısal modellemelerin güvenle kullanılabileceği görülmüştür.

The turbulent wake generated by a rotor interacting with outlet guide vanes (OGVs) is one of the dominant broadband noise sources in a turbofan engine. An accurate representation of the rotor wake turbulence is therefore important for the reliable prediction of the rotor-OGV interaction noise. This paper presents a turbulence synthesis method based on a spectral proper orthogonal decomposition (POD) representation of the turbulent wake that aims to reproduce the desired velocity cross-spectrum along the OGV leading edges where noise is emitted due to turbulence-OGV interaction. The method is first developed in the frequency domain based on a superposition of vortical modes with the appropriate amplitudes. Fourier modes and POD modes are proposed to represent the two-point velocity spectrum. The POD modes will be shown to be highly efficient in reconstructing the flowfield near the tip region where a large-scale coherent structure is present. An extension of the POD synthetic turbulence method to the time domain is also presented by means of a white noise filtering technique to allow the generation of time-varying velocity signals with the desired cross-spectral characteristics. The results show that both the one- and two-point statistics can be closely reproduced. The proposed frequency-domain POD synthetic turbulence method for fan broadband noise prediction for a realistic fan-OGV configuration is illustrated by the use of a frequency-domain linearized Navier-Stokes solver to predict the sound power radiation due to each vortical mode. Overall sound power levels at a number of discrete frequencies are predicted and compared against measured noise data. Agreement is found to be within the uncertainty of the noise sound power measurement. [ABSTRACT FROM AUTHOR]

In ground effect wind-tunnel experiments, fixed plates are widely adopted to replace the moving ground, which will affect the reliability of experimental results. In this paper, a numerical investigation is conducted to study the feasibility of a fixed plate in the chord-dominated static ground effect experiment. The incompressible Reynolds-averaged Navier-Stokes equations and shear stress transport k-ω turbulence model are solved. The feasibility of a fixed plate is determined by the camber effect, the blocking effect, and the boundary-layer effect. The camber effect dominates the suction distribution on the airfoil upper surface, and the blocking and boundary-layer effects together govern the pressure distribution on the lower surface. With the decreasing plate length, the modeling ability of camber effect decreases slightly first and then sharply; and the modeling ability of the blocking effect gradually restores due to the gradually weakened boundary-layer effect. A fixed plate can reproduce the lift and pitching moment accurately due to the accurate duplication of pressure distribution, but it fails in drag due to the inaccurate modeling of shear stress distribution. The optimal fixed plate configurations for different angles of attack and ride heights are given for ground effect wind-tunnel experiments. [ABSTRACT FROM AUTHOR]

The purpose of the NASA Juncture Flow experiment was to acquire high-quality flowfield details deep in the corner of a wing-body junction specifically for the purpose of computational fluid dynamics (CFD) validation. A truncated DLR F6 wing was used along with a flat-sided fuselage with windows that allowed both laser Doppler velocimetry and particle image velocimetry measurements to be made very close to the corner. This paper describes the experiment and its results. It also makes comparisons between the wind-tunnel data and Reynolds-averaged Navier-Stokes CFD results using a new version of a quadratic constitutive relation that was recently developed to improve separated corner-flow predictions. This validation experiment provides useful flowfield data that can be used to test the ability of CFD methods and models to accurately represent separated juncture flow physics. [ABSTRACT FROM AUTHOR]

Transonic buffet is undesirable because it causes vibration, and constraining buffet is crucial in transonic wing design. However, there is still a lack of accurate and efficient buffet formulation to impose the constraint. This work proposes a physics-based data-driven buffet analysis model generalizable for airfoil and wing shapes. The model is trained with data obtained from two-dimensional airfoils in a physics-based manner to extend it to buffet analyses of three-dimensional wings. Specifically, the model takes the pressure and friction distributions as inputs to discover the key physics (shock waves and flow separation) of transonic buffeting, rather than using shape and flow parameters as the input. High-quality sample airfoils are used and a mixture model of convolutional neural networks is proposed to improve accuracy. The model exhibits a mean absolute error of 0.05 deg in buffet factor prediction of 14,886 unseen testing data. Buffet boundary predictions using the model compare well with the reference results (a lift-curve break method) for various airfoils and wings. Wing shape optimization using the model appropriately considers buffet constraints, leading to an optimized wing with lower drag (by 1.7 counts) than that obtained by the state-of-the-art method. These results demonstrate the effectiveness of the proposed physics-based data-driven buffet analysis approach. The proposed method is a promising alternative to address other complex off-design constraints in aircraft design. [ABSTRACT FROM AUTHOR]

A computational investigation of a Mach 6.9 turbulent flow near the juncture (cove) of a wing's trailing-edge and elevon was carried out. Turbulence was modeled using improved delayed detached eddy simulation (IDDES). The computational data were compared to the results of an experimental study, conducted by Deveikis and Bartlett, which simulated the flow over the windward surface of the NASA space shuttle. Flow visualization, surface variable comparison with experiment, and analysis of unsteady flow statistics were carried out. Reasonable agreement between prediction and measurement was obtained for time-averaged surface pressure and heat flux. Unsteady analysis of these quantities revealed spectra dominated by low-frequency energy content throughout the interaction region. A correlation analysis indicated coupling of the unsteady motions of the shear layer, shock wave, separation vortex, and flow reattachment. The results of the present study suggest that IDDES can be a valuable tool for the analysis of heating and unsteadiness in hypersonic gap flows. [ABSTRACT FROM AUTHOR]

This study proposes a sweeping jet as a novel solution to control catastrophic flow-acoustic resonance through a combined experimental and scale-adaptive simulation (SAS) strategy. The relationships between resonance intensity and the geometry of the dual sweeping-jet controllers (SJCs) and mass ratio of the jet flow to mainstream flow were established by the wall-pressure measurements. The system with dual SJCs at two upstream channel-branch intersections with spanwise jet sweeping achieved the best control performance at the low mass ratio of Qr=1%. Through complementary simulations, self-sustained unsteady flow dynamics within dual SJCs, strong flow-acoustic resonance within the channel-branch system and complete suppression of the aeroacoustic field by the most efficient dual SJCs were demonstrated. The simulation results were first validated in terms of the frequency and amplitude information of the experimentally measured wall-pressure fluctuations. Subsequently, a proper orthogonal decomposition analysis was conducted and a large-scale synchronous sweeping behavior was observed when the jet flow proceeded from the fluidic oscillators to the free space. Thereafter, SAS results revealed the dual SJCs could remarkably attenuate velocity fluctuations, shear-layer momentum thickness, and Reynolds and Lighthill stresses. These improvements were achieved by completely suppressing the large-scale shear-layer vortex shedding into a series of horseshoe vortices. [ABSTRACT FROM AUTHOR]

Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of h ¯ near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively. [ABSTRACT FROM AUTHOR]

The influence of surface roughness on overlying turbulence is represented by a drag layer, with a quadratic drag law. The drag coefficient is considered to be a function of effective sandgrain roughness. The challenge to hybrid modeling is posed as being to calibrate that drag law, such that the calibration be nearly the same for either RANS or LES. To that end the coefficient is first calibrated for LES. With roughness represented by the drag formula, the RANS model and boundary condition are adjusted to provide consistency in the log layer. Then, it is found that RANS and LES calibrations become nearly the same. The model is validated by simulations of a rough wall boundary layer, of rough to smooth junction flow, of a rough ramp, and of streamwise roughness strips. [ABSTRACT FROM AUTHOR]

The high-fidelity rotorcraft simulation framework HPCMP CREATE-AV Helios was used to study the impact of turbulence modeling methods on the prediction of a small quadrotor unmanned aerial vehicle. First, the vehicle's rotor was simulated as an isolated rotor in both hover and forward flight for turbulence model assessment. Predictions using a fully turbulent turbulence model were compared with predictions from several laminar-turbulent transition models. Both comparison with experiments and computational performance were considered. The laminar-turbulent transition models predicted flow separation near the tip for all flight conditions simulated, leading to lower torque and thrust than the fully turbulent model, which predicted attached turbulent flow. The fully turbulent model was shown to provide reasonable comparison with experiments with the lowest computational cost and was used for full vehicle simulations. The full quadrotor configuration calculations were performed in hover and forward flight. The forward flight simulations were performed with and without a detached eddy simulation method, and similar interactional aerodynamics were predicted. The Helios simulation suite is shown to be well-suited for prediction of aerodynamic performance of small-scale rotorcraft. [ABSTRACT FROM AUTHOR]

Ensuring the safe operation of new supersonic transport aircraft requires understanding their stability during takeoff and landing. These phases involve flying at subsonic speeds and high angles of attack, where the aerodynamics are characterized by unsteady vortical flow. This work assesses the accuracy of Reynolds-averaged Navier-Stokes (RANS) and delayed detached eddy simulations (DDES) at predicting the vortex-dominated flow over a delta wing for angles of attack up to and past stall. The delta wing has an aspect ratio of 2 and is a simplified representation of a supersonic transport wing. The predicted aerodynamic coefficients are compared with experimental data, focusing on the shape of the pitching moment curve. In addition, a steadiness metric is formulated to distinguish between steady and unsteady angles of attack. It is found that RANS accurately predicts vortex effects in the steady regime but is inaccurate at high angles of attack where the flow is unsteady. DDES is more reliable in the unsteady regime, but the computational cost is at least 100 times that of RANS. Predicting the pitching moment at the highest angles of attack is difficult even with DDES on a 69-million-cell mesh. These results provide guidelines for choosing the appropriate fidelity depending on the flow characteristics, the required accuracy, and the computational budget. [ABSTRACT FROM AUTHOR]

Two kinds of two-stage broken line closure laws of the wicket gates, modified A scheme (MAS) and modified B scheme (MBS), are presented to investigate the relationship between the wicket gates closure law and pressure pulsation shutting down pump turbines. The Detached Eddy Simulation (DES) model that is based on the moving mesh technology, is adopted to simulate the process of closure of the wicket gates. The results are analyzed in the time-domain and the time-frequency domain by Continuous Wavelet Transform (CWT). It was discovered that at the vaneless space, there isa intense pulsation at Blade Passing Frequency (BPF) lasting up to 3s in the original scheme (OS) of linear closure law, while the duration is reduced by 16.17% in MAS and has little change in MBS. At the leading edge of the stay vane, the high amplitude pulsation lasting nearly 1s is observed in OS. However, this pulse duration is reduced by 50% in MAS. Interestingly, in MAS, there is also a stabilization period lasting 1s before the wicket gates are fully closed, which is consistent with the pressure characteristics at the outlet of wicket gate. Moreover, the BPF and low frequency are the main components in the time-frequency plots. And the fluctuation energy at BPF and low frequency in the MAS is significantly smaller than the other two schemes. It is important that the torque duration at BPF is significantly reduced by 35% in MAS and slightly reduced in MBS. It is worth noting that the closure law of wicket gates has great effect on the pressure pulsation at BPF. This study is crucial improving the transient characteristics of pump turbines in pump mode by using the two-stage broken line closure law. [ABSTRACT FROM AUTHOR]

Flow over a cavity is one of the most intriguing problems in aeronautics. Although geometry is simple, the physics of cavity requires uttermost attention. In this study, various novel passive flow control techniques such as reshaping the aft wall as stair-stepped configuration or combinations of spoilers with reshaped aft wall are applied to cavity and effects of these techniques are investigated numerically. Combined configurations that are proposed in the present study are considered as a novelty to the literature. Analyses are performed with Detached Eddy Simulation method three-dimensionally in transonic regime (0.85 Mach) for a Reynolds number of ~107 based on the cavity length, 0.508 m, using open-source software OpenFOAM. Results are compared with both experimental data and each other, fundamentally in terms of Overall Average Sound Pressure Level. Further examinations are also performed for features such as Mach number, turbulent intensity and turbulent coherent structures. It is seen that combined passive flow control methods have reduced Overall Average Sound Pressure Level by ~10 dB. Newly proposed passive flow control methods have also reduced Overall Average Sound Pressure Level by ~6 dB. A high correlation between coherent turbulent structures and generated noise is observed.

The unsteady and extensively separated turbulent airwake flows around a ship's deck significantly impact helicopter pilot performance during shipboard operations. Hence, incorporating realistic, unsteady incoming mainstream conditions such as the atmospheric boundary layer (ABL), is crucial in numerical simulations of the ship airwake. This study employed delayed detached eddy simulations (DDES) to evaluate the effect of steady and unsteady ABL modeling methods on the turbulent flow characteristics of the ship airwake. A 1:12.5 scaled Simple Frigate Shape 1 (SFS1) ship model was utilized in the numerical simulations, and three distinct ABL profiles (one steady and two unsteady) were simulated at two different wind direction angles (HW and RW30). Synthetic and turbulator modeling methods were utilized to generate the unsteady ABL profiles. Time-averaged and instantaneous flow fields calculated by various ABL profiles were compared with experimental data at multiple points within the ship airwake. The numerical findings indicated that while the time-averaged data remained unaffected by the ABL profile presence, the instantaneous flow quantities experienced significant alterations, especially under the red wind condition. The introduction of an unsteady ABL profile was shown to augment the unsteadiness and fluctuation of the flow field within the ship airwake compared to the steady ABL scenario. Cross-correlation analyses between the velocity fields computed using steady and unsteady ABL profiles unveiled distinct patterns and behaviors of flow structures over the deck. Moreover, evaluation of the velocity and pressure fields of unsteady ABL across time/space domains revealed incremented turbulence and disturbances over the flight deck, intensifying with wind direction angle. The synthetic ABL modeling approach was found to deliver promising outcomes in comparison to the turbulator method, while requiring significantly lower computational resources. • The velocity field becomes asymmetric with an increase in wind direction angle. • Mean flow variables are not affected by the unsteady ABL profile. • The synthetic approach replicate the flow characteristic with relatively lower cost than the turbulator. [Display omitted] [ABSTRACT FROM AUTHOR]