Xianbei Huang, Zhuqing Liu and Wei Yang
The purpose of this paper is to bring in and clarify the performance of the Vreman and dynamic Vreman models (VM and DVM) in simulating the internal flow of the centrifugal pump…
Abstract
Purpose
The purpose of this paper is to bring in and clarify the performance of the Vreman and dynamic Vreman models (VM and DVM) in simulating the internal flow of the centrifugal pump impeller.
Design/methodology/approach
Four subgrid scale (SGS) models, including the Smagorinsky model, the dynamic Smagorinsky model, the VM and the DVM are chosen to study the performance in predicting the flow field in the centrifugal pump impeller at design load. The velocity and turbulent kinetic energy distributions are compared. Also, the temporal variation of the model coefficient of the DVM is studied.
Findings
The results of all the four models show agreement with both the PIV and LDV data. It is clarified that the VM and the DVM are adaptive in simulating the turbulent flow in the centrifugal pump at design load, and the DVM shows even better performance in predicting the velocity distribution. Additionally, the temporal variation of the model coefficient of the DVM is about 0.01, which is the optimal value for VM in this study. It is verified that VM can perform as good as the dynamic models when an appropriate model coefficient is chosen.
Originality/value
The applicability of the VM and the DVM in simulating the internal flow of the centrifugal pump has been proven at design load. The introducing of the two models into centrifugal pump’s simulation can provide some new ideas in constructing more adaptive SGS models for this kind of high-rotating flow.
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The present paper is about numerical simulations of one‐ and two‐dimensional lean hydrogen combustion at an equivalence ratio of 0.7. The initial flat two‐dimensional flames show…
Abstract
Purpose
The present paper is about numerical simulations of one‐ and two‐dimensional lean hydrogen combustion at an equivalence ratio of 0.7. The initial flat two‐dimensional flames show unstable behavior. The instabilities generate flame wrinkling and flame induced turbulence. As a result, cusp‐like structures arise that both merge and break up in new cusps. Therefore, physically, the laminar burning velocity associated to an adiabatic flat flame does not exist. Instead, a statistical effective burning velocity and flame width develop in which the cusp like structures and their effects are included. The purpose of this paper is to describe the phenomena with a reduced chemical approach.
Design/methodology/approach
Simulations are performed with detailed kinetics, to study the main properties and dynamics of the wrinkling. An attempt is made to reduce the chemistry employing flamelet generated manifolds to make a step towards large‐scale, low cost simulations, which are still able to capture the physics. Here the manifold was built of premixed flames with variations of stretch, unburnt temperature and equivalence ratio. A priori correlations are presented, together with results from actual reduced chemistry simulations.
Findings
It was found that with introduction of variation of equivalence ratio into the manifold the main physical phenomena are captured. Moreover, an effective inclusion of differential diffusion was succesfully tested and applied. Results of effective burning velocities and flame widths are presented.
Originality/value
The paper shows the potential of performing accurate simulations using the chemical reduction technique of flamelet generated manifolds for pure lean hydrogen flames.
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Sarath Radhakrishnan, Joan Calafell, Arnau Miró, Bernat Font and Oriol Lehmkuhl
Wall-modeled large eddy simulation (LES) is a practical tool for solving wall-bounded flows with less computational cost by avoiding the explicit resolution of the near-wall…
Abstract
Purpose
Wall-modeled large eddy simulation (LES) is a practical tool for solving wall-bounded flows with less computational cost by avoiding the explicit resolution of the near-wall region. However, its use is limited in flows that have high non-equilibrium effects like separation or transition. This study aims to present a novel methodology of using high-fidelity data and machine learning (ML) techniques to capture these non-equilibrium effects.
Design/methodology/approach
A precursor to this methodology has already been tested in Radhakrishnan et al. (2021) for equilibrium flows using LES of channel flow data. In the current methodology, the high-fidelity data chosen for training includes direct numerical simulation of a double diffuser that has strong non-equilibrium flow regions, and LES of a channel flow. The ultimate purpose of the model is to distinguish between equilibrium and non-equilibrium regions, and to provide the appropriate wall shear stress. The ML system used for this study is gradient-boosted regression trees.
Findings
The authors show that the model can be trained to make accurate predictions for both equilibrium and non-equilibrium boundary layers. In example, the authors find that the model is very effective for corner flows and flows that involve relaminarization, while performing rather ineffectively at recirculation regions.
Originality/value
Data from relaminarization regions help the model to better understand such phenomenon and to provide an appropriate boundary condition based on that. This motivates the authors to continue the research in this direction by adding more non-equilibrium phenomena to the training data to capture recirculation as well.
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Zhen Chen, Zhengqi Gu and Zhonggang Wang
This paper aims to propose a precise turbulence model for vehicle aerodynamics, especially for vehicle window buffeting noise.
Abstract
Purpose
This paper aims to propose a precise turbulence model for vehicle aerodynamics, especially for vehicle window buffeting noise.
Design/methodology/approach
Aiming at the fact that commonly used turbulence models cannot precisely predict laminar-turbulent transition, a transition-code-based improvement is introduced. This improvement includes the introduction of total stress limitation (TSL) and separation-sensitive model. They are integrated into low Reynolds number (LRN) k-ε model to concern transport properties of total stress and precisely capture boundary layer separations. As a result, the ability of LRN k-ε model to predict the transition is improved. Combined with the constructing scheme of constrained large-eddy simulation (CLES) model, a modified LRN CLES model is achieved. Several typical flows and relevant experimental results are introduced to validate this model. Finally, the modified LRN CLES model is used to acquire detailed flow structures and noise signature of a simplified vehicle window. Then, experimental validations are conducted.
Findings
Current results indicate that the modified LRN CLES model is capable of achieving acceptable accuracy in prediction of various types of transition at various Reynolds numbers. And, the ability of this model to simulate the vehicle window buffeting noise is greater than commonly used models.
Originality/value
Based on the TSL idea and separation-sensitive model, a modified LRN CLES model concerning the laminar-turbulent transition for the vehicle window buffeting noise is first proposed.
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Peyman Maghsoudi and Mehdi Bidabadi
The purpose of this study is to describe the combustion of a magnesium particle falling into a hot oxidizer medium.
Abstract
Purpose
The purpose of this study is to describe the combustion of a magnesium particle falling into a hot oxidizer medium.
Design/methodology/approach
The governing equations, including mass, momentum and energy conservation equations, are numerically solved. Afterward, the influences of effective parameters on the temperature distribution and burning time are investigated. Artificial neural network (ANN) is applied to approximate the particle temperature as a function of time, diameter and porosity factor. To obtain the best arrangement of the ANN structure, an optimization process is conducted.
Findings
The results show that by considering variations of the particle size, the maximum temperature increases compared to the case in which the particle diameter is constant. Also, the ignition and burning times and the maximum temperature of the moving particle are lower than those of the motionless particle. Optimum network has the best values of regression coefficient and mean relative error whose values are found to be 0.99991 and 1.58 per cent, respectively.
Originality/value
In this study, particle size varies over the combustion process that leads to calculation of particle burning time. In addition, the effects of the motion and porosity of the particle are examined.
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Jéromine Dumon, Yannick Bury, Nicolas Gourdain and Laurent Michel
The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical…
Abstract
Purpose
The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical integrity of the launcher can be compromised by shock wave/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments.
Design/methodology/approach
This paper aims to report numerical and experimental investigations on the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experimental investigations based on Schlieren visualizations are conducted in a transonic wind tunnel and are then compared with numerical predictions based on unsteady Reynolds averaged Navier–Stokes and large eddy simulation (LES) approaches. The effect of buffeting on the structure is finally studied by solving the equation of the dynamics.
Findings
Buffeting is both experimentally and numerically revealed. Experiments highlight 3D oscillations of the shock wave in the manner of a wind-flapping flag. LES computations identify a lambda-shaped shock wave foot width oscillations, which noticeably impact aerodynamic loads. At last, the experiments highlight the chaotic behavior of the shock wave as it shifts from an oscillatory periodic to an erratic 3D flapping state. Fluid structure computations show that the aerodynamic response of the airfoil tends to damp the structural vibrations and to mitigate the effect of buffeting.
Originality/value
While buffeting has been extensively studied for classical supercritical profiles, this study focuses on diamond airfoils. Moreover, a fluid structure computation has been conducted to point out the effect of buffeting.
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Julia Kasch, Margien Bootsma, Veronique Schutjens, Frans van Dam, Arjan Kirkels, Frans Prins and Karin Rebel
In this opinion article, the authors share their experiences with and perspectives on course design requirements and barriers when applying challenge-based learning (CBL) in an…
Abstract
In this opinion article, the authors share their experiences with and perspectives on course design requirements and barriers when applying challenge-based learning (CBL) in an online sustainability education setting. CBL is an established learning approach for (higher) sustainability education. It enables teachers to engage students with open, real-life grand challenges through inter-/transdisciplinary student team collaboration. However, empirical research is scarce and mainly based on face-to-face CBL case studies. Thus far, the opportunities to apply CBL in online educational settings are also underinvestigated.
Using the TPACK framework, the authors address technological, pedagogical and content knowledge related to CBL and online sustainability education. The integration of the different components is discussed, providing teachers and course designers insight into design requirements and barriers.
This paper supports the promising future of online CBL for sustainability education, especially in the context of inter-/national inter-university collaboration, yet emphasizes the need for deliberate use of online collaboration and teaching tools.
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Aoxiang Qiu, Weimin Sang, Feng Zhou and Dong Li
The paper aims to expand the scope of application of the lattice Boltzmann method (LBM), especially in the field of aircraft engineering. The traditional LBM is usually applied…
Abstract
Purpose
The paper aims to expand the scope of application of the lattice Boltzmann method (LBM), especially in the field of aircraft engineering. The traditional LBM is usually applied to incompressible flows at a low Reynolds number, which is not sufficient to satisfy the needs of aircraft engineering. Devoted to tackling the defect, the paper proposes a developed LBM combining the subgrid model and the multiple relaxation time (MRT) approach. A multilayer adaptive Cartesian grid method to improve the computing efficiency of the traditional LBM is also employed.
Design/methodology/approach
The subgrid model and the multilayer adaptive Cartesian grid are introduced into MRT-LBM for simulations of incompressible flows at a high Reynolds number. Validated by several typical flow simulations, the numerical methods in this paper can efficiently study the flows under high Reynolds numbers.
Findings
Some numerical simulations for the lid-driven flow of cavity, flow around iced GLC305, LB606b and ONERA-M6 are completed. The paper presents the investigation results, indicating that the methods are accurate and effective for the separated flow after icing.
Originality/value
LBM is developed with the addition of the subgrid model and the MRT method. A numerical strategy is proposed using a multilayer adaptive Cartesian grid method and its treatment of boundary conditions. The paper refers to innovative algorithm developments and applications to the aircraft engineering, especially for iced wing simulations with flow separations.
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Seyi F. Olatoyinbo, Sarma L. Rani and Abdelkader Frendi
The purpose of this study is to investigate the accuracy and applicability of the Flowfield Dependent Variation (FDV) method for large-eddy simulations (LES) of decaying isotropic…
Abstract
Purpose
The purpose of this study is to investigate the accuracy and applicability of the Flowfield Dependent Variation (FDV) method for large-eddy simulations (LES) of decaying isotropic turbulence.
Design/methodology/approach
In an earlier paper, the FDV method was successfully demonstrated for simulations of laminar flows with speeds varying from low subsonic to high supersonic Mach numbers. In the current study, the FDV method, implemented in a finite element framework, is used to perform LESs of decaying isotropic turbulence. The FDV method is fundamentally derived from the Lax–Wendroff Scheme (LWS) by replacing the explicit time derivatives in LWS with a weighted combination of explicit and implicit time derivatives. The increased implicitness and the inherent numerical dissipation of FDV contribute to the scheme’s numerical stability and monotonicity. Understanding the role of numerical dissipation that is inherent to the FDV method is essential for the maturation of FDV into a robust scheme for LES of turbulent flows. Accordingly, three types of LES of decaying isotropic turbulence were performed. The first two types of LES utilized explicit subgrid scale (SGS) models, namely, the constant-coefficient Smagorinsky and dynamic Smagorinsky models. In the third, no explicit SGS model was employed; instead, the numerical dissipation inherent to FDV was used to emulate the role played by explicit SGS models. Such an approach is commonly known as Implicit LES (ILES). A new formulation was also developed for quantifying the FDV numerical viscosity that principally arises from the convective terms of the filtered Navier–Stokes equations.
Findings
The temporal variation of the turbulent kinetic energy and enstrophy and the energy spectra are presented and analyzed. At all grid resolutions, the temporal profiles of kinetic energy showed good agreement with t(−1.43) theoretical scaling in the fully developed turbulent flow regime, where t represents time. The energy spectra also showed reasonable agreement with the Kolmogorov’s k(−5/3) power law in the inertial subrange, with the spectra moving closer to the Kolmogorov scaling at higher-grid resolutions. The intrinsic numerical viscosity and the dissipation rate of the FDV scheme are quantified, both in physical and spectral spaces, and compared with those of the two SGS LES runs. Furthermore, at a finite number of flow realizations, the numerical viscosities of FDV and of the Streamline Upwind/Petrov–Galerkin (SUPG) finite element method are compared. In the initial stages of turbulence development, all three LES cases have similar viscosities. But, once the turbulence is fully developed, implicit LES is less dissipative compared to the two SGS LES runs. It was also observed that the SUPG method is significantly more dissipative than the three LES approaches.
Research limitations/implications
Just as any computational method, the limitations are based on the available computational resources.
Practical implications
Solving problems involving turbulent flows is by far the biggest challenge facing engineers and scientists in the twenty-first century, this is the road that the authors have embarked upon in this paper and the road ahead of is very long.
Social implications
Understanding turbulence is a very lofty goal and a challenging one as well; however, if the authors succeed, the rewards are limitless.
Originality/value
The derivation of an explicit expression for the numerical viscosity tensor of FDV is an important contribution of this study, and is a crucial step forward in elucidating the fundamental properties of the FDV method. The comparison of viscosities for the three LES cases and the SUPG method has important implications for the application of ILES approach for turbulent flow simulations.
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Nicolas Gourdain, Jéromine Dumon, Yannick Bury and Pascal Molton
The transonic buffet is a complex aerodynamics phenomenon that imposes severe constraints on the design of high-speed vehicles, including for aircraft and space launchers. The…
Abstract
Purpose
The transonic buffet is a complex aerodynamics phenomenon that imposes severe constraints on the design of high-speed vehicles, including for aircraft and space launchers. The origin of buffet is still debated in the literature, and the control of this phenomenon remains difficult. This paper aims to propose an original scenario to explain the origin of buffet, which in turn opens promising perspectives for its alleviation and attenuation.
Design/methodology/approach
This work relies on the use of numerical simulations, with the idea to reproduce the buffet phenomenon in a transonic aileron designed for small space launchers. Two numerical approaches are tested: unsteady Reynolds averaged Navier–Stokes (URANS) and large-eddy simulation (LES). The numerical predictions are first validated against available experimental data, before to be analysed in detail to identify the origin of buffet on the studied configuration. A complementary numerical study is then conducted to assess the possibility to delay the onset of buffet.
Findings
The buffet control strategy is based on wall cooling. By adequately choosing the wall temperature, this work shows that it is feasible to delay the emergence of buffet. More precisely, this paper highlights the crucial role of the subsonic flow inside the boundary layer, showing the existence of upstream travelling pressure waves that are responsible for the flow coupling between both sides of the airfoil, at the origin of the buffet phenomenon.
Originality/value
This paper proposes a new scenario to explain the origin of buffet, based on the use of a Fanno and Rayleigh flow analogies. This approach is used to design a control solution based on a modification of the wall temperature, showing very promising results.