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Construct a new sub-grid scale (SGS) model which can improve the efficiency and maintain comparative accuracy comparing to the existing dynamic cubic non-linear SGS model (DCNM).

The polynomial constitutive relation between the SGS stress tensor and both strain and rotation rate is selected as a basement. Simplification is achieved by eliminating the solid-body rotation term and adopting the assumption proposed by Kosovic. A dynamic procedure is applied to calculate three model coefficients in the new model. The new model (named dynamic simplified Lund model) and DCNM are applied to the rotating channel flow and the internal flow in a centrifugal pump impeller to examine the performance.

The new model is as accurate as DCNM but decreases 25 per cent computational resources. The ability of capturing rotation effect and reflecting backscatter is verified through cases. In addition, good numerical stability is shown during the calculation.

More benchmark and engineering cases should be used to get further confidence on the new model.

The new model is promising in industrial application with the advantage of both accuracy and efficiency. For the flow with large-scale separation or more complicate phenomenon, the model is thought to give accurate flow structure.

A new non-linear SGS model is proposed in this paper. The accuracy, numerical stability and efficiency are validated for this model. Therefore, it is promising in the prediction of the flow structure in centrifugal pumps.

The purpose of this paper is to obtain a better understanding of the rotor–stator interaction in the vaneless region of a centrifugal pump.

A third-order sub-grid scale (SGS) model containing the rotation rate tensor named the dynamic cubic non-linear model (DCNM) is used for simulating the flow field in a centrifugal pump with a vaned diffuser. The pressure coefficient and velocity distributions are compared with the experimental data. Focusing on the vaneless region, the pressure pulsation, Reynolds stress pulsation and Reynolds stress transport equation are analyzed.

The comparison of the calculation results with the experimental data indicates that the DCNM can accurately capture the distributions of pressure and velocity in the vaneless region. Based on the instantaneous pressure signals, the pressure pulsation is analyzed to show that in the vaneless region, the dominant frequency near the impeller is twice the blade passing frequency, whereas it is equal to the blade passing frequency near the diffuser. Further exploration of the Reynolds stress pulsation shows the correlation between the two variables. Additionally, the extreme low frequency of Reynolds stress near the diffuser is found to be related to the rotation instability. To explore the turbulence characteristics in the vaneless region, the Reynolds stress transportation equation is studied. In the vaneless region, the rotation term of the Reynolds stress transport equation is negligible compared to the production term, although the rotation instability is obvious near the diffuser. The production of the Reynolds stress plays the role of redistributing the energy from the uu component to the vv component, except for the region near the impeller outlet.

The third-order SGS model DCNM has proved to be promising in simulating the rotor–stator interaction. The analysis of the rotation instability and the Reynolds stress transport equation shed light on the further understanding of the rotor–stator interaction.

This paper aims to address the performance of different subgrid-scale models (SGS) for hydro- (HD) and magnetohydrodynamic (MHD) channel flows within a collocated finite-volume scheme.

First, the SGS energy transfer is analyzed by a priori tests using fully resolved DNS data. Here, the focus lies on the influence of the magnetic field on the SGS energy transport. Second, the authors performed a series of 18 a posteriori model tests, using different grid resolutions and SGS models for HD and MHD channel flows.

From the a priori analysis, the authors observe a quantitative reduction of the SGS energy transport because of the action of the magnetic field depending on its orientation. The a posteriori model tests show a clear improvement because of the use of mixed-models within the numerical scheme.

This study demonstrates the necessity of improved SGS modeling strategies for magnetohydrodynamic channel flows within a collocated finite-volume scheme.

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.

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.

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.

Just as any computational method, the limitations are based on the available computational resources.

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.

Understanding turbulence is a very lofty goal and a challenging one as well; however, if the authors succeed, the rewards are limitless.

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.

Large eddy simulation (LES) is widely used in prediction of turbulent flow. The purpose of this paper is to propose a new dynamic mixed nonlinear subgrid‐scale (SGS) model (DMNM), in order to improve LES precision of complex turbulent flow, such as flow including separation or rotation.

The SGS stress in DMNM consists of scale‐similarity part and eddy‐viscosity part. The scale‐similarity part is used to describe the energy transfer of scales that are close to the cut‐off explicitly. The eddy‐viscosity part represents energy transfer of the other scales between smaller than grid‐filter size and larger than grid‐filter size. The model is demonstrated through two examples; one is channel flow and another is surface‐mounted cube flow. The computed results are compared with prior experimental data, and the behavior of DMNM is analyzed.

The proposed model has the following characteristics. First, DMNM exhibits significant flexibility in self‐calibration of the model coefficients. Second, it does not require alignment of the principal axes of the SGS stress tensor and the resolved strain rate tensor. Third, since both the rotating part and scale‐similarity part are considered in the new model, flow with rotation and separation is easily simulated. Compared with the prior experimental data, DMNM gives more accurate results in both examples.

The SGS model DMNM proposed in the paper could capture the detail vortex characteristics more accurately. It has the advantage in simulation of complex flow, including more separations.

Oscillations and related stability problems of synchronous generators are harmful and can lead to power outage. Studies have shown that currently available commercial applications of power system stabilizers (PSSs) do not ensure damping of modern generators operating in contemporary power systems at peak performances. The purpose of this paper is to contribute to development of the new PSS, which would replace currently used linear stabilizers.

A synthesis of theoretical research, numerical simulations and laboratory experiments was the basic framework.

Within a problem analysis, it was empirically confirmed that the currently used PSSs are not up to the needs of the present power systems. Based on an analysis of the contemporary solutions, it was found out that the most appropriate solutions are adaptive control and robust control. In this paper, the robust sliding mode theory was implemented for the PSS design.

The most notable restriction of rapid transfer of scientific solutions into a practice represents limited testing of proposed solutions on synchronous generators in power plants.

The new PSS which would replace currently used conventional stabilizers will have an exceptional value for all producers of the excitation systems.

The originality of the paper represents the development of the new robust sliding mode PSS and qualitative assessment of the developed stabilizer with two competitive stabilizers, i.e. the conventional linear- and advanced direct adaptive-PSS.

Hybrid Reynolds-averaged Navier–Stokes large eddy simulation (RANS-LES) methods have become popular for simulation of massively separated flows at high Reynolds numbers due to their reduced computational cost and good accuracy. The current study aims to examine the performance of LES and hybrid RANS-LES model for a given grid resolution.

For better assessment and contrast of model performance, both mean and instantaneous flow fields have been investigated. For studying instantaneous flow, proper orthogonal decomposition has been used.

Current analysis shows that hybrid RANS-LES is capable of achieving similar accuracy in prediction of both mean and instantaneous flow fields at a very coarse grid as compared to LES.

Focusing mostly on the practical applications of computation, most of the attention has been given to the prediction of one-point flow statistics and little consideration has been put to two-point statistics. Here, two-point statistics has been considered using POD to investigate unsteady turbulent flow.

A computational fluid dynamics code for the calculation of laminar hypersonic multi‐species gas flows in chemical non‐equilibrium in axisymmetric or two‐dimensional configuration on shared and distributed memory parallel computers is presented and validated. The code is designed to work efficiently in combination with an automatic domain decompositioning method developed to facilitate efficient parallel computations of various flow problems.

The baseline implicit numerical method developed is the lower‐upper symmetric Gauss‐Seidel scheme, which is combined with a sub‐iteration scheme to achieve time‐accuracy up to third‐order. The spatial discretisation is based on Roe's flux‐difference splitting and various non‐linear flux limiters maintaining total‐variation diminishing properties and up to third‐order spatial accuracy in continuous regions of flow. The domain subdivision procedure is designed to work for single‐ and multi‐block domains without being constrained by the block boundaries, and an arbitrary number of processors used for the computation.

The code developed reproduces accurately various types of flows, e.g. flow over a flat plate, diffusive mixing and oscillating shock induced combustion around a projectile fired into premixed gas, and demonstrates close to linear scalability within limits of load imbalance.

The cases considered are axisymmetric or two‐dimensional, and assume laminar flow. An extension to three‐dimensional turbulent flows is left for future work.

Results of a parallel computation, utilising a newly developed automatic domain subdivision procedure, for oscillating shock‐induced combustion around a projectile and various other cases are presented. The influence of entropy correction in Roe's flux‐difference splitting algorithm on diffusive mixing of multi‐species flows was examined.

The purpose of this paper is to assess the Boussinesq approach for a wide range of Ra (10 × 6 to 10 × 11) in two-dimensional (square cavity) and three-dimensional (cubic cavity) problems for air- and liquid-filled domains.

The thermal behavior in “differentially heated cavities” filled with air (low and medium Rayleigh) and water (high Rayleigh) is solved using computational fluid dynamics (CFDs) (OpenFOAM) with a non-compressible (Boussinesq) and compressible approach (real water properties from the IAPWS database).

The results from the wide range of Rayleigh numbers allowed for the establishment of the limitation of the Boussinesq approach in problems where the fluid has significant density changes within the operation temperature range and especially when the dependence of density with temperature is not linear. For these cases, the symmetry behavior predicted by Boussinesq is far from the compressible results, thus inducing a transient heat imbalance and leading to a higher mean temperature.

The main limitation of the present research can be found in the shortage of experimental data for very high Rayleigh problems.

Practical implications of the current research could be use of the Boussinesq approach by carefully observing its limitations, especially for sensible problems such as the study of pressure vessels, nuclear reactors, etc.

The originality of this paper lies in addressing the limitations of the Boussinesq approach for high Rayleigh water systems. This fluid is commonly used in numerous industrial equipment. This work presents valuable conclusions about the limitations of the currently used models to carry out industrial simulations.

The Lattice Boltzmann (LB) method offers an alternative to conventional computational fluid dynamics (CFD) methods. However, its practical use for complex turbulent flows of engineering interest is still at an early stage. This paper aims to outline an LB wall-modeled large-eddy simulation (WMLES) solver.

The solver is dedicated to complex high-Reynolds flows in the context of WMLES. It relies on an improved LB scheme and can handle complex geometries on multi-resolution block structured grids.

Dynamic and acoustic characteristics of a turbulent airflow past a rod-airfoil tandem are examined to test the capabilities of this solver. Detailed direct comparisons are made with both experimental and numerical reference data.

This study allows assessing the potential of an LB approach for industrial CFD applications.